Vera C. Rubin Observatory

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Vera C. Rubin Observatory

Rendering of completed LSST
Alternative names	LSST
Named after	Vera Rubin
Location(s)	Elqui Province, Coquimbo Region, Chile
Coordinates	30°14′40.7″S 70°44′57.9″WCoordinates: 30°14′40.7″S 70°44′57.9″W
Organization	Large Synoptic Survey Telescope Corporation
Altitude	2,663 m (8,737 ft), top of pier
Wavelength	320–1060 nm
Built	2015–2021
First light	Expected in 2023
Telescope style	Three-mirror anastigmat, Paul-Baker / Mersenne-Schmidt wide-angle
Diameter	8.417 m (27.6 ft) physical 8.360 m (27.4 ft) optical 5.116 m (16.8 ft) inner
Secondary diameter	3.420 m (1.800 m inner)
Tertiary diameter	5.016 m (1.100 m inner)
Angular resolution	0.7″ median seeing limit 0.2″ pixel size
Collecting area	35 square meters (376.7 sq ft)
Focal length	10.31 m (f/1.23) overall 9.9175 m (f/1.186) primary
Mounting	altazimuth mount
Website	www.vro.org/,%20https://www.lsst.org/

Artist's conception of the LSST inside its dome. The LSST will carry out a deep, ten-year imaging survey in six broad optical bands over the main survey area of 18,000 square degrees.

The Vera C. Rubin Observatory, previously referred to as the Large Synoptic Survey Telescope (LSST), is an astronomical observatory currently under construction in Chile. Its main task will be carrying out a synoptic astronomical survey, the Legacy Survey of Space and Time (LSST). The word synoptic is derived from the Greek words σύν (syn "together") and ὄψις (opsis "view"), and describes observations that give a broad view of a subject at a particular time. The observatory is located on the El Peñón peak of Cerro Pachón, a 2,682-meter-high mountain in Coquimbo Region, in northern Chile, alongside the existing Gemini South and Southern Astrophysical Research Telescopes. The LSST Base Facility is located about 100 kilometres (62 mi) away by road, in the town of La Serena. The observatory is named for Vera Rubin, an American astronomer who pioneered discoveries about galaxy rotation rates.

The Rubin Observatory will house the Simonyi Survey Telescope, a wide-field reflecting telescope with an 8.4-meter primary mirror that will photograph the entire available sky every few nights. The telescope uses a novel three-mirror design, a variant of three-mirror anastigmat, which allows a compact telescope to deliver sharp images over a very wide 3.5-degree diameter field of view. Images will be recorded by a 3.2-gigapixel CCD imaging camera, the largest digital camera ever constructed.

The LSST was proposed in 2001, and construction of the mirror began (with private funds) in 2007. LSST then became the top-ranked large ground-based project in the 2010 Astrophysics Decadal Survey, and the project officially began construction 1 August 2014 when the National Science Foundation (NSF) authorized the FY2014 portion ($27.5 million) of its construction budget. Funding comes from the NSF, the United States Department of Energy, and private funding raised by the dedicated international non-profit organization, the LSST Corporation. Operations are under the management of the Association of Universities for Research in Astronomy (AURA).

Site construction began on 14 April 2015 with the ceremonial laying of the first stone. First light for the engineering camera is expected in July 2023, while system first light is expected in February 2024 and full survey operations are aimed to begin in October 2024, due to COVID-related schedule delays. LSST data is scheduled to become fully public after two years.

Name

In June 2019, the renaming of the Large Synoptic Survey Telescope (LSST) to the Vera C. Rubin Observatory was initiated by Rep. Eddie Bernice Johnson and Jenniffer González-Colón. The renaming was enacted into law on December 20, 2019. The official renaming was announced at the 2020 American Astronomical Society winter meeting. The observatory is named after Vera C. Rubin. The name honors Rubin and her colleagues' legacy to probe the nature of dark matter by mapping and cataloging billions of galaxies through space and time.

The telescope will be named the Simonyi Survey Telescope, to acknowledge the private donors Charles and Lisa Simonyi.

History

The L1 lens for the LSST, 2018

The LSST is the successor to a long tradition of sky surveys. These started as visually compiled catalogs in the 18th century, such as the Messier catalog. This was replaced by photographic surveys, starting with the 1885 Harvard Plate Collection, the National Geographic Society – Palomar Observatory Sky Survey, and others. By about 2000, the first digital surveys, such as the Sloan Digital Sky Survey (SDSS), began to replace the photographic plates of the earlier surveys.

LSST evolved from the earlier concept of the Dark Matter Telescope, mentioned as early as 1996. The fifth decadal report, Astronomy and Astrophysics in the New Millennium, was released in 2001, and recommended the "Large-Aperture Synoptic Survey Telescope" as a major initiative. Even at this early stage the basic design and objectives were set:

The Large-aperture Synoptic Survey Telescope (LSST) is a 6.5-m-class optical telescope designed to survey the visible sky every week down to a much fainter level than that reached by existing surveys. It will catalog 90 percent of the near-Earth objects larger than 300 m and assess the threat they pose to life on Earth. It will find some 10,000 primitive objects in the Kuiper Belt, which contains a fossil record of the formation of the solar system. It will also contribute to the study of the structure of the universe by observing thousands of supernovae, both nearby and at large redshift, and by measuring the distribution of dark matter through gravitational lensing. All the data will be available through the National Virtual Observatory... providing access for astronomers and the public to very deep images of the changing night sky.

Early development was funded by a number of small grants, with major contributions in January 2008 by software billionaires Charles and Lisa Simonyi and Bill Gates of $20- and $10 million respectively. $7.5 million was included in the U.S. President's FY2013 NSF budget request. The Department of Energy is funding construction of the digital camera component by the SLAC National Accelerator Laboratory, as part of its mission to understand dark energy.

In the 2010 decadal survey, LSST was ranked as the highest-priority ground-based instrument.

NSF funding for the rest of construction was authorized as of 1 August 2014. The lead organizations are:

• The SLAC National Accelerator Laboratory to design and construct the LSST camera
• The National Optical Astronomy Observatory to provide the telescope and site team
• The National Center for Supercomputing Applications to construct and test the archive and data access center
• The Association of Universities for Research in Astronomy is responsible for overseeing the LSST construction.

As of May 2022, the project critical path was the camera installation, integration and testing.

In May 2018, Congress surprisingly appropriated much more funding than the telescope had asked for, in hopes of speeding up construction and operation. Telescope management was thankful but unsure this would help, since at the late stage of construction they were not cash-limited.

Overview

The Simonyi Survey Telescope design is unique among large telescopes (8 m-class primary mirrors) in having a very wide field of view: 3.5 degrees in diameter, or 9.6 square degrees. For comparison, both the Sun and the Moon, as seen from Earth, are 0.5 degrees across, or 0.2 square degrees. Combined with its large aperture (and thus light-collecting ability), this will give it a spectacularly large etendue of 319 m²∙degree². This is more than three times the etendue of the largest-view existing telescopes, the Subaru Telescope with its Hyper Suprime Camera and Pan-STARRS, and more than an order of magnitude better than most large telescopes.

Optics

The LSST primary/tertiary mirror successfully cast, August 2008.

 

Optics of the LSST Telescope.

The Simonyi Survey Telescope is the latest in a long line of improvements giving telescopes larger fields of view. The earliest reflecting telescopes used spherical mirrors, which although easy to fabricate and test, suffer from spherical aberration; a very long focal length was needed to reduce spherical aberration to a tolerable level. Making the primary mirror parabolic removes spherical aberration on-axis, but the field of view is then limited by off-axis coma. Such a parabolic primary, with either a prime or Cassegrain focus, was the most common optical design up through the Hale telescope in 1949. After that, telescopes used mostly the Ritchey–Chrétien design, using two hyperbolic mirrors to remove both spherical aberration and coma, leaving only astigmatism, and giving a wider useful field of view. Most large telescopes since the Hale use this design—the Hubble and Keck telescopes are Ritchey–Chrétien, for example. LSST will use a three-mirror anastigmat to cancel astigmatism by employing three non-spherical mirrors. The result is sharp images over a very wide field of view, but at the expense of light-gathering power due to the large tertiary mirror.

The telescope's primary mirror (M1) is 8.4 meters (28 ft) in diameter, the secondary mirror (M2) is 3.4 meters (11.2 ft) in diameter, and the tertiary mirror (M3), inside the ring-like primary, is 5.0 meters (16 ft) in diameter. The secondary mirror is expected to be the largest convex mirror in any operating telescope, until surpassed by the ELT's 4.2 m secondary in about 2024. The second and third mirrors reduce the primary mirror's light-collecting area to 35 square meters (376.7 sq ft), equivalent to a 6.68-meter-diameter (21.9 ft) telescope. Multiplying this by the field of view produces an étendue of 336 m²∙degree²; the actual figure is reduced by vignetting.

The primary and tertiary mirrors (M1 and M3) are designed as a single piece of glass, the "M1M3 monolith". Placing the two mirrors in the same location minimizes the overall length of the telescope, making it easier to reorient quickly. Making them out of the same piece of glass results in a stiffer structure than two separate mirrors, contributing to rapid settling after motion.

The optics includes three corrector lenses to reduce aberrations. These lenses, and the telescope's filters, are built into the camera assembly. The first lens at 1.55 m diameter is the largest lens ever built, and the third lens forms the vacuum window in front of the focal plane.

Unlike many telescopes, the Rubin Observatory makes no attempt to compensate for dispersion in the atmosphere. Such correction, which requires re-adjusting an additional element in the optical train, would be very difficult in the 5 seconds allowed between pointings, plus is a technical challenge due to the extremely short focal length. As a result, shorter wavelength bands away from the zenith will have somewhat reduced image quality.

Camera

Life-size model of the LSST focal plane array. The array's diameter is 64 cm, and will provide over 3 gigapixels per image. The image of the Moon (30 arcminutes) is present to show the scale of the field of view. The model is held by Suzanne Jacoby, the Rubin Observatory communications director.

A 3.2-gigapixel prime focus digital camera will take a 15-second exposure every 20 seconds. Repointing such a large telescope (including settling time) within 5 seconds requires an exceptionally short and stiff structure. This in turn implies a very small f-number, which requires very precise focusing of the camera.

The 15-second exposures are a compromise to allow spotting both faint and moving sources. Longer exposures would reduce the overhead of camera readout and telescope re-positioning, allowing deeper imaging, but then fast moving objects such as near-Earth objects would move significantly during an exposure. Each spot on the sky is imaged with two consecutive 15 second exposures, to efficiently reject cosmic ray hits on the CCDs.

The camera focal plane is flat and 64 cm in diameter. The main imaging is performed by a mosaic of 189 CCD detectors, each with 16 megapixels. They are grouped into a 5×5 grid of "rafts", where the central 21 rafts contain 3×3 imaging sensors, while the four corner rafts contain only three CCDs each, for guiding and focus control. The CCDs provide better than 0.2 arcsecond sampling, and will be cooled to approximately −100 °C (173 K) to help reduce noise.

The camera includes a filter located between the second and third lenses, and an automatic filter-changing mechanism. Although the camera has six filters (ugrizy) covering 330 to 1080 nm wavelengths, the camera's position between the secondary and tertiary mirrors limits the size of its filter changer. It can only hold five filters at a time, so each day one of the six must be chosen to be omitted for the following night.

Image data processing

Scan of Flammarion engraving taken with LSST in September 2020.

Allowing for maintenance, bad weather and other contingencies, the camera is expected to take over 200,000 pictures (1.28 petabytes uncompressed) per year, far more than can be reviewed by humans. Managing and effectively analyzing the enormous output of the telescope is expected to be the most technically difficult part of the project. In 2010, the initial computer requirements were estimated at 100 teraflops of computing power and 15 petabytes of storage, rising as the project collects data. By 2018, estimates had risen to 250 teraflops and 100 petabytes of storage.

Once images are taken, they are processed according to three different timescales, prompt (within 60 seconds), daily, and annually.

The prompt products are alerts, issued within 60 seconds of observation, about objects that have changed brightness or position relative to archived images of that sky position. Transferring, processing, and differencing such large images within 60 seconds (previous methods took hours, on smaller images) is a significant software engineering problem by itself. Approximately 10 million alerts will be generated per night. Each alert will include the following:

• Alert and database ID: IDs uniquely identifying this alert
• The photometric, astrometric, and shape characterization of the detected source
• 30×30 pixel (on average) cut-outs of the template and difference images (in FITS format)
• The time series (up to a year) of all previous detections of this source
• Various summary statistics ("features") computed of the time series

There is no proprietary period associated with alerts—they are available to the public immediately, since the goal is to quickly transmit nearly everything LSST knows about any given event, enabling downstream classification and decision making. LSST will generate an unprecedented rate of alerts, hundreds per second when the telescope is operating. Most observers will be interested in only a tiny fraction of these events, so the alerts will be fed to "event brokers" which forward subsets to interested parties. LSST will provide a simple broker, and provide the full alert stream to external event brokers. The Zwicky Transient Facility will serve as a prototype of LSST system, generating 1 million alerts per night.

Daily products, released within 24 hours of observation, comprise the images from that night, and the source catalogs derived from difference images. This includes orbital parameters for Solar System objects. Images will be available in two forms: Raw Snaps, or data straight from the camera, and Single Visit Images, which have been processed and include instrumental signature removal (ISR), background estimation, source detection, deblending and measurements, point spread function estimation, and astrometric and photometric calibration.

Annual release data products will be made available once a year, by re-processing the entire science data set to date. These include:

• Calibrated images
• Measurements of positions, fluxes, and shapes
• Variability information
• A compact description of light curves
• A uniform reprocessing of the difference-imaging-based prompt data products
• A catalog of roughly 6 million Solar Systems objects, with their orbits
• A catalog of approximately 37 billion sky objects (20 billion galaxies and 17 billion stars), each with more than 200 attributes

The annual release will be computed partially by NCSA, and partially by IN2P3 in France.

LSST is reserving 10% of its computing power and disk space for user generated data products. These will be produced by running custom algorithms over the LSST data set for specialized purposes, using Application Program Interfaces (APIs) to access the data and store the results. This avoids the need to download, then upload, huge quantities of data by allowing users to use the LSST storage and computation capacity directly. It also allows academic groups to have different release policies than LSST as a whole.

An early version of the LSST image data processing software is being used by the Subaru telescope's Hyper Suprime-Cam instrument, a wide-field survey instrument with a sensitivity similar to LSST but one fifth the field of view: 1.8 square degrees versus the 9.6 square degrees of LSST.

Scientific goals

Comparison of primary mirrors of several optical telescopes. (The LSST, with its very large central hole, is near the center of the diagram).

LSST will cover about 18,000 deg² of the southern sky with 6 filters in its main survey, with about 825 visits to each spot. The 5σ (SNR greater than 5) magnitude limits are expected to be r<24.5 in single images, and r<27.8 in the full stacked data.

The main survey will use about 90% of the observing time. The remaining 10% will be used to obtain improved coverage for specific goals and regions. This includes very deep (r ∼ 26) observations, very short revisit times (roughly one minute), observations of "special" regions such as the Ecliptic, Galactic plane, and the Large and Small Magellanic Clouds, and areas covered in detail by multi-wavelength surveys such as COSMOS and the Chandra Deep Field South. Combined, these special programs will increase the total area to about 25,000 deg².

Particular scientific goals of the LSST include:

• Studying dark energy and dark matter by measuring weak gravitational lensing, baryon acoustic oscillations, and photometry of type Ia supernovae, all as a function of redshift.
• Mapping small objects in the Solar System, particularly near-Earth asteroids and Kuiper belt objects. LSST is expected to increase the number of cataloged objects by a factor of 10–100. It will also help with the search for the hypothesized Planet Nine.
• Detecting transient astronomical events including novae, supernovae, gamma-ray bursts, quasar variability, and gravitational lensing, and providing prompt event notifications to facilitate follow-up.
• Mapping the Milky Way.

Because of its wide field of view and high sensitivity, LSST is expected to be among the best prospects for detecting optical counterparts to gravitational wave events detected by LIGO and other observatories.

It is also hoped that the vast volume of data produced will lead to additional serendipitous discoveries.

NASA has been tasked by the US Congress with detecting and cataloging 90% of the NEO population of size 140 meters or greater. LSST, by itself, is estimated to be capable of detecting 62% of such objects, and according to the National Academy of Sciences, extending its survey from ten years to twelve would be the most cost-effective way of finishing the task.

Rubin Observatory has a program of Education and Public Outreach (EPO). Rubin Observatory EPO will serve four main categories of users: the general public, formal educators, citizen science principal investigators, and content developers at informal science education facilities. Rubin Observatory will partner with Zooniverse for a number of their citizen science projects.

Comparison with other sky surveys

Top-end assembly lowered by 500-ton crane

There have been many other optical sky surveys, some still on-going. For comparison, here are some of the main currently used optical surveys, with differences noted:

• Photographic sky surveys, such as the National Geographic Society – Palomar Observatory Sky Survey and its digitized version, the Digitized Sky Survey. This technology is obsolete, with much less depth, and in general taken from locations with less than excellent views. However, these archives are still used since they span a rather large time interval—more than 100 years in some cases—and cover the entire sky. The plate scans reached a limit of R~18 and B~19.5 over 90% of the sky, and about one magnitude fainter over 50% of the sky.
• The Sloan Digital Sky Survey (SDSS) (2000–2009) surveyed 14,555 square degrees of the northern hemisphere sky with a 2.5 meter telescope. It continues to the present day as a spectrographic survey. Its limiting photometric magnitude ranged from 20.5 to 22.2, depending on the filter.
• Pan-STARRS (2010–present) is an ongoing sky survey using two wide-field 1.8 m Ritchey–Chrétien telescopes located at Haleakala in Hawaii. Until LSST begins operation, it will remain the best detector of near-Earth objects. Its coverage, 30,000 square degrees, is comparable to what LSST will cover. The single image depth in the PS1 survey was between magnitude 20.9-22.0 depending on filter.
• The DESI Legacy Imaging Surveys (2013–present) looks at 14,000 square degrees of the northern and southern sky with the Bok 2.3-m telescope, the 4-meter Mayall telescope and the 4-meter Victor M. Blanco Telescope. The Legacy Surveys make use of the Mayall z-band Legacy Survey, the Beijing-Arizona Sky Survey and the Dark Energy Survey. The Legacy Surveys avoided the Milky Way since it was primarily concerned with distant galaxies. The area of DES (5,000 square degrees) is entirely contained within the anticipated survey area of LSST in the southern sky. Its exposures typically reach magnitude 23-24.
• Gaia is an ongoing space-based survey of the entire sky since 2014, whose primary goal is extremely precise astrometry of roughly two billion stars, quasars, galaxies and sun system objects. Its collecting area of 0.7 m² does not allow observation of objects as faint as can be included in other surveys, but the location of each object observed is known with far greater precision. While not taking exposures in the traditional sense, it detects objects up to a magnitude of 21.
• The Zwicky Transient Facility (2018–present) is a similar, rapid, wide-field survey to detect transient events. The telescope has an even larger field of view (47 square degrees; 5× the field), but a significantly smaller aperture (1.22 m; 1/30 the area). It is being used to develop and test the LSST automated alert software. Its exposures typically reach magnitude 20-21.
• The Space Surveillance Telescope (2011–present) is a similar rapid wide-field survey telescope used primarily for military applications, with secondary civil applications including space debris and NEO detection and cataloguing.

Construction progress

Construction progress of the LSST observatory building at Cerro Pachón as of September 2019

The Cerro Pachón site was selected in 2006. The main factors were the number of clear nights per year, seasonal weather patterns, and the quality of images as seen through the local atmosphere (seeing). The site also needed to have an existing observatory infrastructure, to minimize costs of construction, and access to fiber optic links, to accommodate the 30 terabytes of data LSST will produce each night.

As of February 2018, construction was well underway. The shell of the summit building is complete, and 2018 saw the installation of major equipment, including HVAC, the dome, mirror coating chamber, and the telescope mount assembly. It also saw the expansion of the AURA base facility in La Serena and the summit dormitory shared with other telescopes on the mountain.

By February 2018, the camera and telescope shared the critical path. The main risk was deemed to be whether sufficient time was allotted for system integration.

As of 2017 the project remained within budget, although the budget contingency was tight.

In March 2020, work on the summit facility, and the main camera at SLAC, was suspended due to the COVID-19 pandemic, though work on software continued. During this time, the commissioning camera arrived at the base facility and is being tested there. It will be moved to the summit when it is safe to do so.

Mirrors

The primary mirror, the most critical and time-consuming part of a large telescope's construction, was made over a 7-year period by the University of Arizona's Steward Observatory Mirror Lab. Construction of the mold began in November 2007, mirror casting was begun in March 2008, and the mirror blank was declared "perfect" at the beginning of September 2008. In January 2011, both M1 and M3 figures had completed generation and fine grinding, and polishing had begun on M3.

The mirror was formally accepted on 13 February 2015, then placed in the mirror transport box and stored in an airplane hangar. In October 2018, it was moved back to the mirror lab and integrated with the mirror support cell. It went through additional testing in January/February 2019, then was returned to its shipping crate. In March 2019, it was sent by truck to Houston, was placed on a ship for delivery to Chile, and arrived on the summit in May. There it will be re-united with the mirror support cell and coated.

The coating chamber, which was used to coat the mirrors once they arrived, itself arrived at the summit in November 2018.

The secondary mirror was manufactured by Corning of ultra low expansion glass and coarse-ground to within 40 μm of the desired shape. In November 2009, the blank was shipped to Harvard University for storage until funding to complete it was available. On 21 October 2014, the secondary mirror blank was delivered from Harvard to Exelis (now a subsidiary of Harris Corporation) for fine grinding. The completed mirror was delivered to Chile on 7 December 2018, and was coated in July 2019.

Building

Cutaway rendering of the telescope, dome, and support building.

Site excavation began in earnest on 8 March 2011, and the site had been leveled by the end of 2011. Also during that time, the design progressed, with significant improvements to the mirror support system, stray-light baffles, wind screen, and calibration screen.

In 2015, a large amount of broken rock and clay was found under the site of the support building adjacent to the telescope. This caused a 6-week construction delay while it was dug out and the space filled with concrete. This did not affect the telescope proper or its dome, whose much more important foundations were examined more thoroughly during site planning.

The building was declared substantially complete in March 2018. The dome was expected to be complete in August 2018, but a picture from May 2019 showed it still incomplete. The (still incomplete) Rubin Observatory dome first rotated under its own power in November 2019.

Telescope mount assembly

Telescope Mount Assembly of the 8.4-meter Simonyi Survey Telescope at Vera C. Rubin Observatory, under construction atop Cerro Pachón in Chile.

The telescope mount, and the pier on which it sits, are substantial engineering projects in their own right. The main technical problem is that the telescope must slew 3.5 degrees to the adjacent field and settle within four seconds. This requires a very stiff pier and telescope mount, with very high speed slew and acceleration (10°/sec and 10°/sec², respectively). The basic design is conventional: an altitude over azimuth mount made of steel, with hydrostatic bearings on both axes, mounted on a pier which is isolated from the dome foundations. However, the LSST pier is unusually large (16 m diameter) and robust (1.25 m thick walls), and mounted directly to virgin bedrock, where care was taken during site excavation to avoid using explosives that would crack it. Other unusual design features are linear motors on the main axes and a recessed floor on the mount. This allows the telescope to extend slightly below the azimuth bearings, giving it a very low center of gravity.

The contract for the Telescope Mount Assembly was signed in August 2014. It passed its acceptance tests in 2018 and arrived at the construction site in September 2019.

Camera construction

In August 2015, the LSST Camera project, which is separately funded by the U.S. Department of Energy, passed its "critical decision 3" design review, with the review committee recommending DoE formally approve start of construction. On August 31, the approval was given, and construction began at SLAC. As of September 2017, construction of the camera was 72% complete, with sufficient funding in place (including contingencies) to finish the project. By September 2018, the cryostat was complete, the lenses ground, and 12 of the 21 needed rafts of CCD sensors had been delivered. As of September 2020, the entire focal plane was complete and undergoing testing. By October 2021, the last of the six filters needed by the camera had been finished and delivered. By November 2021, the entire camera had been cooled down to its required operating temperature, so final testing could begin.

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  Rendering of the LSST camera.

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  Color-coded cutaway drawing of the LSST camera.

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  Exploded view of the optical components of the LSST camera.

Before the final camera is installed, a smaller and simpler version (the Commissioning Camera, or ComCam) will be used "to perform early telescope alignment and commissioning tasks, complete engineering first light, and possibly produce early usable science data".

Data transport

The data must be transported from the camera, to facilities at the summit, to the base facilities, and then to the LSST Data Facility at the National Center for Supercomputing Applications in the United States. This transfer must be very fast (100 Gbit/s or better) and reliable since NCSA is where the data will be processed into scientific data products, including real-time alerts of transient events. This transfer uses multiple fiber optic cables from the base facility in La Serena to Santiago, then via two redundant routes to Miami, where it connects to existing high speed infrastructure. These two redundant links were activated in March 2018 by the AmLight consortium.

Since the data transfer crosses international borders, many different groups are involved. These include the Association of Universities for Research in Astronomy (AURA, Chile and the USA), REUNA (Chile), Florida International University (USA), AmLightExP (USA), RNP (Brazil), and University of Illinois at Urbana–Champaign NCSA (USA), all of which participate in the LSST Network Engineering Team (NET). This collaboration designs and delivers end-to-end network performance across multiple network domains and providers.

Possible impact of satellite constellations

A study in 2020 by the European Southern Observatory estimated that up to 30% to 50% of the exposures around twilight with the Rubin Observatory would be severely affected by satellite constellations. Survey telescopes have a large field of view and they study short-lived phenomena like supernova or asteroids, and mitigation methods that work on other telescopes may be less effective. The images would be affected especially during twilight (50%) and at the beginning and end of the night (30%). For bright trails the complete exposure could be ruined by a combination of saturation, crosstalk (far away pixels gaining signal due to the nature of CCD electronics), and ghosting (internal reflections within the telescope and camera) caused by the satellite trail, affecting an area of the sky significantly larger than the satellite path itself during imaging. For fainter trails only a quarter of the image would be lost. A previous study by the Rubin Observatory found an impact of 40% at twilight and only nights in the middle of the winter would be unaffected.

Possible approaches to this problem would be a reduction of the number or brightness of satellites, upgrades to the telescope's CCD camera system, or both. Observations of Starlink satellites showed a decrease of the satellite trail brightness for darkened satellites. This decrease is however not enough to mitigate the effect on wide-field surveys like the one conducted by the Rubin Observatory. Therefore SpaceX is introducing a sunshade on newer satellites, to keep the portions of the satellite visible from the ground out of direct sunlight. The objective is to keep the satellites below 7th magnitude, to avoid saturating the detectors. This limits the problem to only the trail of the satellite and not the whole image.

Gallery

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  Clear Skies at Cerro Pachón 

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  Vera C. Rubin Observatory under construction 

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  Telescope mount assembly, taken from the dome during bridge crane installation. 

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  Focal plane of the LSST Cam. It is 60 cm (2 feet) wide, has 189 sensors to produce 3200-megapixel images. 

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  Optical engineers Justin Wolfe (left) and Simon Cohen with the r filter for the LSST Cam. 

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  The LSST Cam chilled to subzero temperatures using both cooling systems 

Psychosynthesis

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Psychosynthesis

Psychosynthesis is an approach to psychology that expands the boundaries of the field by identifying a deeper center of identity, which is the postulate of the Self. It considers each individual unique in terms of purpose in life, and places value on the exploration of human potential. The approach combines spiritual development with psychological healing by including the life journey of an individual or their unique path to self-realization.

The integrative framework of psychosynthesis is based on Sigmund Freud's theory of the unconscious and addresses psychological distress and intra-psychic and interpersonal conflicts.

Development

Psychosynthesis was developed by Italian psychiatrist, Roberto Assagioli, who was a student of Freud and Bleuler. He compared psychosynthesis to the prevailing thinking of the day, contrasting psychosynthesis for example with existential psychology, but unlike the latter considered loneliness not to be "either ultimate or essential".

Assagioli asserted that "the direct experience of the self, of pure self-awareness...—is true." Spiritual goals of "self-realization" and the "interindividual psychosynthesis"—of "social integration...the harmonious integration of the individual into ever larger groups up to the 'one humanity'"—were central to Assagioli's theory. Psychosynthesis was not intended to be a school of thought or an exclusive method. However, many conferences and publications had it as a central theme, and centres were formed in Italy and the United States in the 1960s.

Psychosynthesis departed from the empirical foundations of psychology because it studied a person as a personality and a soul, but Assagioli continued to insist that it was scientific. He developed therapeutic methods beyond those in psychoanalysis. Although the unconscious is an important part of his theory, Assagioli was careful to maintain a balance with rational, conscious therapeutical work.

Assagioli was not the first to use the term "psychosynthesis". The earliest use was by James Jackson Putnam, who used it as the name of his electroconvulsive therapy. The term was also used by C. G. Jung and A. R. Orage, who were both more aligned to Assagioli's use of the term than Putnam's use. C. G. Jung, in comparing his goals to those of Sigmund Freud, wrote, "If there is a 'psychoanalysis' there must also be a 'psychosynthesis which creates future events according to the same laws'." A. R. Orage, who was the publisher of the influential journal, The New Age, used the term as well, but hyphenated it (psycho-synthesis). Orage formed an early psychology study group (which included Maurice Nicoll who later studied with Carl Jung) and concluded that what humanity needed was not psychoanalysis, but psycho-synthesis. The term was also used by Bezzoli. Freud, however, was opposed to what he saw as the directive element in Jung's approach to psychosynthesis, and Freud argued for a spontaneous synthesis on the patient's part: "As we analyse...the great unity which we call his ego fits into itself all the instinctual impulses which before had been split off and held apart from it. The psycho-synthesis is thus achieved in analytic treatment without our intervention, automatically and inevitably."

Origins

In 1909, C.G. Jung wrote to Sigmund Freud of "a very pleasant and perhaps valuable acquaintance, our first Italian, a Dr. Assagioli from the psychiatric clinic in Florence". Later however, this same Roberto Assagioli (1888 – 1974) wrote a doctoral dissertation, "La Psicosintesi," in which he began to move away from Freud's psychoanalysis toward what he called psychosynthesis:

A beginning of my conception of psychosynthesis was contained in my doctoral thesis on Psychoanalysis (1910), in which I pointed out what I considered to be some of the limitations of Freud's views.

In developing psychosynthesis, Assagioli agreed with Freud that healing childhood trauma and developing a healthy ego were necessary aims of psychotherapy, but Assagioli believed that human growth could not be limited to this alone. A student of philosophical and spiritual traditions of both East and West, Assagioli sought to address human growth as it proceeded beyond the norm of the well-functioning ego; he wished to support the fruition of human potential—what Abraham Maslow later termed self-actualization—into the spiritual or transpersonal dimensions of human experience as well.

Assagioli envisioned an approach to the human being that could address both the process of personal growth—of personality integration and self-actualization—as well as transpersonal development—that dimension glimpsed for example in peak experiences (Maslow) of inspired creativity, spiritual insight, and unitive states of consciousness. Psychosynthesis recognizes the process of self-realization, of contact and response with one's deepest callings and directions in life, which can involve either or both personal and transpersonal development.

Psychosynthesis is therefore one of the earliest forerunners of both humanistic psychology and transpersonal psychology, even preceding Jung's break with Freud by several years. Assagioli's conception has an affinity with existential-humanistic psychology and other approaches that attempt to understand the nature of the healthy personality, personal responsibility, and choice, and the actualization of the personal self. Similarly, his conception is related to the field of transpersonal psychology (with its focus on higher states of consciousness), spirituality, and human experience beyond the individual self. Assagioli served on the board of editors for both the Journal of Humanistic Psychology and the Journal of Transpersonal Psychology.

Assagioli presents two major theoretical models in his seminal book, Psychosynthesis, models that have remained fundamental to psychosynthesis theory and practice:

1. A diagram and description of the human person
2. A stage theory of the process of psychosynthesis (see below).

Aims

In Psychosomatic Medicine and Bio-psychosynthesis, Assagioli states that the principal aims and tasks of psychosynthesis are:

1. the elimination of the conflicts and obstacles, conscious and unconscious, that block [the complete and harmonious development of the human personality]
2. the use of active techniques to stimulate the psychic functions still weak and immature.

In his major book, Psychosynthesis: A Collection of Basic Writings (1965), Assagioli writes of three aims of psychosynthesis:

Let us examine whether and how it is possible to solve this central problem of human life, to heal this fundamental infirmity of man. Let us see how he may free himself from this enslavement and achieve an harmonious inner integration, true Self-realization, and right relationships with others. (p. 21)

Model of the person

Psychosynthesis Egg Diagram

 

1: Lower Unconscious

2: Middle Unconscious

3: Higher Unconscious

4: Field of Consciousness

5: Conscious Self or "I"

6: Higher Self

7: Collective Unconscious

At the core of psychosynthesis theory is the Egg Diagram, which maps the human psyche into different distinct and interconnected levels.

Lower unconscious

For Assagioli, 'the lower unconscious, which contains one's personal psychological past in the form of repressed complexes, long-forgotten memories and dreams and imaginations', stood at the base of the diagram of the mind.

The lower unconscious is that realm of the person to which is relegated the experiences of shame, fear, pain, despair, and rage associated with primal wounding suffered in life. One way to think of the lower unconscious is that it is a particular bandwidth of one's experiential range that has been broken away from consciousness. It comprises that range of experience related to the threat of personal annihilation, of destruction of self, of nonbeing, and more generally, of the painful side of the human condition. As long as this range of experience remains unconscious, the person will have a limited ability to be empathic with self or others in the more painful aspects of human life.

At the same time, 'the lower unconscious merely represents the most primitive part of ourselves...It is not bad, it is just earlier '. Indeed, 'the "lower" side has many attractions and great vitality', and – as with Freud's id, or Jung's shadow – the conscious goal must be to 'achieve a creative tension' with the lower unconscious.

Middle unconscious

The middle unconscious is a sector of the person whose contents, although unconscious, nevertheless support normal conscious functioning in an ongoing way (thus it is illustrated as most immediate to "I"). It is the capacity to form patterns of skills, behaviors, feelings, attitudes, and abilities that can function without conscious attention, thereby forming the infrastructure of one's conscious life.

The function of the middle unconscious can be seen in all spheres of human development, from learning to walk and talk, to acquiring languages, to mastering a trade or profession, to developing social roles. Anticipating today's neuroscience, Assagioli even referred to "developing new neuromuscular patterns". All such elaborate syntheses of thought, feeling, and behavior are built upon learnings and abilities that must eventually operate unconsciously.

For Assagioli, 'Human healing and growth that involves work with either the middle or the lower unconscious is known as personal psychosynthesis '.

Higher unconscious

Assagioli termed 'the sphere of aesthetic experience, creative inspiration, and higher states of consciousness...the higher unconscious '. The higher unconscious (or superconscious) denotes "our higher potentialities which seek to express themselves, but which we often repel and repress" (Assagioli). As with the lower unconscious, this area is by definition not available to consciousness, so its existence is inferred from moments in which contents from that level affect consciousness. Contact with the higher unconscious can be seen in those moments, termed peak experiences by Maslow, which are often difficult to put into words, experiences in which one senses deeper meaning in life, a profound serenity and peace, a universality within the particulars of existence, or perhaps a unity between oneself and the cosmos. This level of the unconscious represents an area of the personality that contains the "heights" overarching the "depths" of the lower unconscious. As long as this range of experience remains unconscious – in what Desoille termed '"repression of the sublime"' – the person will have a limited ability to be empathic with self or other in the more sublime aspects of human life.

The higher unconscious thus represents 'an autonomous realm, from where we receive our higher intuitions and inspirations – altruistic love and will, humanitarian action, artistic and scientific inspiration, philosophic and spiritual insight, and the drive towards purpose and meaning in life'. It may be compared to Freud's superego, seen as 'the higher, moral, supra-personal side of human nature...a higher nature in man', incorporating 'Religion, morality, and a social sense – the chief elements in the higher side of man...putting science and art to one side'.

Subpersonalities

Subpersonalities based in the personal unconscious form a central strand in psychosynthesis thinking. 'One of the first people to have started really making use of subpersonalities for therapy and personal growth was Roberto Assagioli', psychosynthesis reckoning that 'subpersonalities exist at various levels of organization, complexity, and refinement' throughout the mind. A five-fold process of recognition, acceptance, co-ordination, integration, and synthesis 'leads to the discovery of the Transpersonal Self, and the realization that that is the final truth of the person, not the subpersonalities'.

Some subpersonalities may be seen 'as psychological contents striving to emulate an archetype...degraded expressions of the archetypes of higher qualities '. Others will resist the process of integration; will 'take the line that it is difficult being alive, and it is far easier – and safer – to stay in an undifferentiated state'.

"I"

Psychosynthesis Star Diagram

Psychosynthesis Star Diagram
formulated by Roberto Assagioli

"I" is the direct "reflection" or "projection" of Self (Assagioli) and the essential being of the person, distinct but not separate from all contents of experience. "I" possesses the two functions of consciousness, or awareness, and will, whose field of operation is represented by the concentric circle around "I" in the oval diagram – Personal Will.

Psychosynthesis suggests that "we can experience the will as having four stages. The first stage could be described as 'having no will'", and might perhaps be linked with the hegemony of the lower unconscious. "The next stage of the will is understanding that 'will exists'. We might still feel that we cannot actually do it, but we know...it is possible". "Once we have developed our will, at least to some degree, we pass to the next stage which is called 'having a will'", and thereafter "in psychosynthesis we call the fourth and final stage of the evolution of the will in the individual 'being will'" – which then "relates to the 'I' or self...draws energy from the transpersonal self".

The "I" is placed at the center of the field of awareness and will in order to indicate that "I" is the one who has consciousness and will. It is "I" who is aware of the psyche-soma contents as they pass in and out of awareness; the contents come and go, while "I" may remain present to each experience as it arises. But "I" is dynamic as well as receptive: "I" has the ability to affect the contents of awareness and can even affect awareness itself, by choosing to focus awareness (as in many types of meditation), expand it, or contract it.

Since "I" is distinct from any and all contents and structures of experience, "I" can be thought of as not a "self" at all but as "noself". That is, "I" is never the object of experience. "I" is who can experience, for example, the ego disintegrating and reforming, who can encounter emptiness and fullness, who can experience utter isolation or cosmic unity, who can engage any and all arising experiences. "I" is not any particular experience but the experiencer, not object but subject, and thus cannot be seen or grasped as an object of consciousness. This "noself" view of "I" can be seen in Assagioli's discussion of "I" as a reflection of Self: "The reflection appears to be self-existent but has, in reality, no autonomous substantiality. It is, in other words, not a new and different light but a projection of its luminous source". The next section describes this "luminous source", Self.

Self

Pervading all the areas mapped by the oval diagram, distinct but not separate from all of them, is Self (which has also been called Higher Self or Transpersonal Self). The concept of Self points towards a source of wisdom and guidance within the person, a source which can operate quite beyond the control of the conscious personality. Since Self pervades all levels, an ongoing lived relationship with Self—Self-realization—may lead anywhere on the diagram as one's direction unfolds (this is one reason for not illustrating Self at the top of the diagram, a representation that tends to give the impression that Self-realization leads only into the higher unconscious). Relating to Self may lead for example to engagement with addictions and compulsions, to the heights of creative and religious experience, to the mysteries of unitive experience, to issues of meaning and mortality, to grappling with early childhood wounding, to discerning a sense of purpose and meaning in life.

The relationship of "I" and Self is paradoxical. Assagioli was clear that "I" and Self were from one point of view, one. He wrote, "There are not really two selves, two independent and separate entities. The Self is one". Such a nondual unity is a fundamental aspect of this level of experience. But Assagioli also understood that there could be a meaningful relationship between the person and Self as well:

Accounts of religious experiences often speak of a "call" from God, or a "pull" from some Higher Power; this sometimes starts a "dialogue" between the man [or woman] and this "higher Source"...

Assagioli did not of course limit this relationship and dialogue to those dramatic experiences of "call" seen in the lives of great men and women throughout history. Rather, the potential for a conscious relationship with Self exists for every person at all times and may be assumed to be implicit in every moment of every day and in every phase of life, even when one does not recognize this. Whether within one's private inner world of feelings, thoughts, and dreams, or within one's relationships with other people and the natural world, a meaningful ongoing relationship with Self may be lived.

Stages

Writing about the model of the person presented above, Assagioli states that it is a "structural, static, almost 'anatomical' representation of our inner constitution, while it leaves out its dynamic aspect, which is the most important and essential one". Thus he follows this model immediately with a stage theory outlining the process of psychosynthesis. This scheme can be called the "stages of psychosynthesis", and is presented here.

It is important to note that although the linear progression of the following stages does make logical sense, these stages may not in fact be experienced in this sequence; they are not a ladder up which one climbs, but aspects of a single process. Further, one never outgrows these stages; any stage can be present at any moment throughout the process of Psychosynthesis, Assaglioli acknowledging 'persisting traits belonging to preceding psychological ages' and the perennial possibility of 'retrogression to primitive stages'.

The stages of Psychosynthesis may be tabulated as follows:

1. Thorough knowledge of one's personality.
2. Control of its various elements.
3. Realization of one's true Self—the discovery or creation of a unifying center.
4. Psychosynthesis: the formation or reconstruction of the personality around a new center.

Methods

Psychosynthesis was regarded by Assagioli as more of an orientation and a general approach to the whole human being, and as existing apart from any of its particular concrete applications. This approach allows for a wide variety of techniques and methods to be used within the psychosynthesis context. 'Dialogue, Gestalt techniques, dream work, guided imagery, affirmations, and meditation are all powerful tools for integration', but 'the attitude and presence of the guide are of far greater importance than the particular methods used'. Sand tray, art therapy, journaling, drama therapy, and body work; cognitive-behavioral techniques; object relations, self psychology, and family systems approaches, may all be used in different contexts, from individual and group psychotherapy, to meditation and self-help groups. Psychosynthesis offers an overall view which can help orient oneself within the vast array of different modalities available today, and be applied either for therapy or for self-actualization.

Recently, two psychosynthesis techniques were shown to help student sojourners in their acculturation process. First, the self-identification exercise eased anxiety, an aspect of culture shock. Secondly, the subpersonality model aided students in their ability to integrate a new social identity. In another recent study, the subpersonality model was shown to be an effective intervention for aiding creative expression, helping people connect to different levels of their unconscious creativity. Most recently, psychosynthesis psychotherapy has proven to activate personal and spiritual growth in self-identified atheists.

One broad classification of the techniques used involves the following headings: ' Analytical: To help identify blocks and enable the exploration of the unconscious'. Psychosynthesis stresses 'the importance of using obstacles as steps to growth' – 'blessing the obstacle...blocks are our helpers'. ' Mastery...the eight psychological functions need to be gradually retrained to produce permanent positive change'. ' Transformation...the refashioning of the personality around a new centre'. ' Grounding...into the concrete terms of daily life. ' Relational...to cultivate qualities such as love, openness and empathy'.

Psychosynthesis allows practitioners the recognition and validation of an extensive range of human experience: the vicissitudes of developmental difficulties and early trauma; the struggle with compulsions, addictions, and the trance of daily life; the confrontation with existential identity, choice, and responsibility; levels of creativity, peak performance, and spiritual experience; and the search for meaning and direction in life. None of these important spheres of human existence need be reduced to the other, and each can find its right place in the whole. This means that no matter what type of experience is engaged, and no matter what phase of growth is negotiated, the complexity and uniqueness of the person may be respected—a fundamental principle in any application of psychosynthesis.

Criticism

In the December 1974 issue of Psychology Today, Assagioli was interviewed by Sam Keen and was asked to comment on the limits of psychosynthesis. He answered paradoxically: "The limit of psychosynthesis is that it has no limits. It is too extensive, too comprehensive. Its weakness is that it accepts too much. It sees too many sides at the same time and that is a drawback."

Psychosynthesis "has always been on the fringes of the 'official' therapy world" and it "is only recently that the concepts and methods of psychoanalysis and group analysis have been introduced into the training and practice of psychosynthesis psychotherapy".

As a result, the movement has been at times exposed to the dangers of fossilisation and cultism, so that on occasion, having "started out reflecting the high-minded spiritual philosophy of its founder, [it] became more and more authoritarian, more and more strident in its conviction that psychosynthesis was the One Truth".

A more technical danger is that premature concern with the transpersonal may hamper dealing with personal psychosynthesis: for example, "evoking serenity ... might produce a false sense of well-being and security". Practitioners have noted how "inability to ... integrate the superconscious contact with everyday experience easily leads to inflation", and have spoken of "an 'Icarus complex', the tendency whereby spiritual ambition fails to take personality limitations into account and causes all sorts of psychological difficulties".

Fictional analogies

Stephen Potter's "Lifemanship Psycho-Synthesis Clinic", where you may "find the psycho-synthesist lying relaxed on the couch while the patient will be encouraged to walk up and down" would seem a genuine case of "parallel evolution", since its clear targets, as "the natural antagonists...of the lifeplay, are the psychoanalysts".

Ligand

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Ligand 

Cobalt complex HCo(CO)₄ with five ligands

In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's electron pairs often through Lewis Bases. The nature of metal–ligand bonding can range from covalent to ionic. Furthermore, the metal–ligand bond order can range from one to three. Ligands are viewed as Lewis bases, although rare cases are known to involve Lewis acidic "ligands".

Metals and metalloids are bound to ligands in almost all circumstances, although gaseous "naked" metal ions can be generated in a high vacuum. Ligands in a complex dictate the reactivity of the central atom, including ligand substitution rates, the reactivity of the ligands themselves, and redox. Ligand selection requires critical consideration in many practical areas, including bioinorganic and medicinal chemistry, homogeneous catalysis, and environmental chemistry.

Ligands are classified in many ways, including: charge, size (bulk), the identity of the coordinating atom(s), and the number of electrons donated to the metal (denticity or hapticity). The size of a ligand is indicated by its cone angle.

History

The composition of coordination complexes have been known since the early 1800s, such as Prussian blue and copper vitriol. The key breakthrough occurred when Alfred Werner reconciled formulas and isomers. He showed, among other things, that the formulas of many cobalt(III) and chromium(III) compounds can be understood if the metal has six ligands in an octahedral geometry. The first to use the term "ligand" were Alfred Werner and Carl Somiesky, in relation to silicon chemistry. The theory allows one to understand the difference between coordinated and ionic chloride in the cobalt ammine chlorides and to explain many of the previously inexplicable isomers. He resolved the first coordination complex called hexol into optical isomers, overthrowing the theory that chirality was necessarily associated with carbon compounds.

Strong field and weak field ligands

Main article: Crystal field theory

In general, ligands are viewed as electron donors and the metals as electron acceptors, i.e., respectively, Lewis bases and Lewis acids. This description has been semi-quantified in many ways, e.g. ECW model. Bonding is often described using the formalisms of molecular orbital theory.

Ligands and metal ions can be ordered in many ways; one ranking system focuses on ligand 'hardness' (see also hard/soft acid/base theory). Metal ions preferentially bind certain ligands. In general, 'hard' metal ions prefer weak field ligands, whereas 'soft' metal ions prefer strong field ligands. According to the molecular orbital theory, the HOMO (Highest Occupied Molecular Orbital) of the ligand should have an energy that overlaps with the LUMO (Lowest Unoccupied Molecular Orbital) of the metal preferential. Metal ions bound to strong-field ligands follow the Aufbau principle, whereas complexes bound to weak-field ligands follow Hund's rule.

Binding of the metal with the ligands results in a set of molecular orbitals, where the metal can be identified with a new HOMO and LUMO (the orbitals defining the properties and reactivity of the resulting complex) and a certain ordering of the 5 d-orbitals (which may be filled, or partially filled with electrons). In an octahedral environment, the 5 otherwise degenerate d-orbitals split in sets of 2 and 3 orbitals (for a more in depth explanation, see crystal field theory).

3 orbitals of low energy: d_xy, d_xz and d_yz

2 of high energy: d_z² and d_x²−y²

The energy difference between these 2 sets of d-orbitals is called the splitting parameter, Δ_o. The magnitude of Δ_o is determined by the field-strength of the ligand: strong field ligands, by definition, increase Δ_o more than weak field ligands. Ligands can now be sorted according to the magnitude of Δ_o (see the table below). This ordering of ligands is almost invariable for all metal ions and is called spectrochemical series.

For complexes with a tetrahedral surrounding, the d-orbitals again split into two sets, but this time in reverse order.

2 orbitals of low energy: d_z² and d_x²−y²

3 orbitals of high energy: d_xy, d_xz and d_yz

The energy difference between these 2 sets of d-orbitals is now called Δ_t. The magnitude of Δ_t is smaller than for Δ_o, because in a tetrahedral complex only 4 ligands influence the d-orbitals, whereas in an octahedral complex the d-orbitals are influenced by 6 ligands. When the coordination number is neither octahedral nor tetrahedral, the splitting becomes correspondingly more complex. For the purposes of ranking ligands, however, the properties of the octahedral complexes and the resulting Δ_o has been of primary interest.

The arrangement of the d-orbitals on the central atom (as determined by the 'strength' of the ligand), has a strong effect on virtually all the properties of the resulting complexes. E.g., the energy differences in the d-orbitals has a strong effect in the optical absorption spectra of metal complexes. It turns out that valence electrons occupying orbitals with significant 3 d-orbital character absorb in the 400–800 nm region of the spectrum (UV–visible range). The absorption of light (what we perceive as the color) by these electrons (that is, excitation of electrons from one orbital to another orbital under influence of light) can be correlated to the ground state of the metal complex, which reflects the bonding properties of the ligands. The relative change in (relative) energy of the d-orbitals as a function of the field-strength of the ligands is described in Tanabe–Sugano diagrams.

In cases where the ligand has low energy LUMO, such orbitals also participate in the bonding. The metal–ligand bond can be further stabilised by a formal donation of electron density back to the ligand in a process known as back-bonding. In this case a filled, central-atom-based orbital donates density into the LUMO of the (coordinated) ligand. Carbon monoxide is the preeminent example a ligand that engages metals via back-donation. Complementarily, ligands with low-energy filled orbitals of pi-symmetry can serve as pi-donor.

Metal–EDTA complex, wherein the aminocarboxylate is a hexadentate (chelating) ligand.

 

Cobalt(III) complex containing six ammonia ligands, which are monodentate. The chloride is not a ligand.

Classification of ligands as L and X

Main article: Covalent bond classification method

Especially in the area of organometallic chemistry, ligands are classified as L and X (or combinations of the two). The classification scheme – the "CBC Method" for Covalent Bond Classification – was popularized by M.L.H. Green and "is based on the notion that there are three basic types [of ligands]... represented by the symbols L, X, and Z, which correspond respectively to 2-electron, 1-electron and 0-electron neutral ligands." Another type of ligand worthy of consideration is the LX ligand which as expected from the used conventional representation will donate three electrons if NVE (Number of Valence Electrons) required. Example is alkoxy ligands( which is regularly known as X ligand too). L ligands are derived from charge-neutral precursors and are represented by amines, phosphines, CO, N₂, and alkenes. X ligands typically are derived from anionic precursors such as chloride but includes ligands where salts of anion do not really exist such as hydride and alkyl. Thus, the complex IrCl(CO)(PPh₃)₂ is classified as an MXL₃ complex, since CO and the two PPh₃ ligands are classified as Ls. The oxidative addition of H₂ to IrCl(CO)(PPh₃)₂ gives an 18e⁻ ML₃X₃ product, IrClH₂(CO)(PPh₃)₂. EDTA⁴⁻ is classified as an L₂X₄ ligand, as it features four anions and two neutral donor sites. Cp is classified as an L₂X ligand.

Polydentate and polyhapto ligand motifs and nomenclature

Denticity

Main articles: Denticity and chelate

Denticity (represented by κ) refers to the number of times a ligand bonds to a metal through noncontiguous donor sites. Many ligands are capable of binding metal ions through multiple sites, usually because the ligands have lone pairs on more than one atom. Ligands that bind via more than one atom are often termed chelating. A ligand that binds through two sites is classified as bidentate, and three sites as tridentate. The "bite angle" refers to the angle between the two bonds of a bidentate chelate. Chelating ligands are commonly formed by linking donor groups via organic linkers. A classic bidentate ligand is ethylenediamine, which is derived by the linking of two ammonia groups with an ethylene (−CH₂CH₂−) linker. A classic example of a polydentate ligand is the hexadentate chelating agent EDTA, which is able to bond through six sites, completely surrounding some metals. The number of times a polydentate ligand binds to a metal centre is symbolized by "κⁿ", where n indicates the number of sites by which a ligand attaches to a metal. EDTA⁴⁻, when it is hexidentate, binds as a κ⁶-ligand, the amines and the carboxylate oxygen atoms are not contiguous. In practice, the n value of a ligand is not indicated explicitly but rather assumed. The binding affinity of a chelating system depends on the chelating angle or bite angle.

Complexes of polydentate ligands are called chelate complexes. They tend to be more stable than complexes derived from monodentate ligands. This enhanced stability, the chelate effect, is usually attributed to effects of entropy, which favors the displacement of many ligands by one polydentate ligand. When the chelating ligand forms a large ring that at least partially surrounds the central atom and bonds to it, leaving the central atom at the centre of a large ring. The more rigid and the higher its denticity, the more inert will be the macrocyclic complex. Heme is a good example: the iron atom is at the centre of a porphyrin macrocycle, being bound to four nitrogen atoms of the tetrapyrrole macrocycle. The very stable dimethylglyoximate complex of nickel is a synthetic macrocycle derived from the anion of dimethylglyoxime.

Hapticity

Main article: Hapticity

Hapticity (represented by η) refers to the number of contiguous atoms that comprise a donor site and attach to a metal center. Butadiene forms both η² and η⁴ complexes depending on the number of carbon atoms that are bonded to the metal.

Ligand motifs

Trans-spanning ligands

Main article: Trans-spanning ligand

Trans-spanning ligands are bidentate ligands that can span coordination positions on opposite sides of a coordination complex.

Ambidentate ligand

Main article: Linkage isomerism

Unlike polydentate ligands, ambidentate ligands can attach to the central atom in two places. A good example of this is thiocyanate, SCN⁻, which can attach at either the sulfur atom or the nitrogen atom. Such compounds give rise to linkage isomerism. Polyfunctional ligands, see especially proteins, can bond to a metal center through different ligand atoms to form various isomers.

Bridging ligand

Main article: Bridging ligand

A bridging ligand links two or more metal centers. Virtually all inorganic solids with simple formulas are coordination polymers, consisting of metal ion centres linked by bridging ligands. This group of materials includes all anhydrous binary metal ion halides and pseudohalides. Bridging ligands also persist in solution. Polyatomic ligands such as carbonate are ambidentate and thus are found to often bind to two or three metals simultaneously. Atoms that bridge metals are sometimes indicated with the prefix "μ". Most inorganic solids are polymers by virtue of the presence of multiple bridging ligands. Bridging ligands, capable of coordinating multiple metal ions, have been attracting considerable interest because of their potential use as building blocks for the fabrication of functional multimetallic assemblies.

Binucleating ligand

Main article: Binucleating_ligand

Binucleating ligands bind two metal ions. Usually binucleating ligands feature bridging ligands, such as phenoxide, pyrazolate, or pyrazine, as well as other donor groups that bind to only one of the two metal ions.

Metal–ligand multiple bond

Main article: Metal–ligand multiple bond

Some ligands can bond to a metal center through the same atom but with a different number of lone pairs. The bond order of the metal ligand bond can be in part distinguished through the metal ligand bond angle (M−X−R). This bond angle is often referred to as being linear or bent with further discussion concerning the degree to which the angle is bent. For example, an imido ligand in the ionic form has three lone pairs. One lone pair is used as a sigma X donor, the other two lone pairs are available as L-type pi donors. If both lone pairs are used in pi bonds then the M−N−R geometry is linear. However, if one or both these lone pairs is nonbonding then the M−N−R bond is bent and the extent of the bend speaks to how much pi bonding there may be. η¹-Nitric oxide can coordinate to a metal center in linear or bent manner.

Spectator ligand

Main article: Spectator ligand

A spectator ligand is a tightly coordinating polydentate ligand that does not participate in chemical reactions but removes active sites on a metal. Spectator ligands influence the reactivity of the metal center to which they are bound.

Bulky ligands

Main article: Ligand cone angle

Bulky ligands are used to control the steric properties of a metal center. They are used for many reasons, both practical and academic. On the practical side, they influence the selectivity of metal catalysts, e.g., in hydroformylation. Of academic interest, bulky ligands stabilize unusual coordination sites, e.g., reactive coligands or low coordination numbers. Often bulky ligands are employed to simulate the steric protection afforded by proteins to metal-containing active sites. Of course excessive steric bulk can prevent the coordination of certain ligands. 

 

The N-heterocyclic carbene ligand called IMes is a bulky ligand by virtue of the pair of mesityl groups.

Chiral ligands

Main article: Chiral ligand

Chiral ligands are useful for inducing asymmetry within the coordination sphere. Often the ligand is employed as an optically pure group. In some cases, such as secondary amines, the asymmetry arises upon coordination. Chiral ligands are used in homogeneous catalysis, such as asymmetric hydrogenation.

Hemilabile ligands

Main article: Hemilability

Hemilabile ligands contain at least two electronically different coordinating groups and form complexes where one of these is easily displaced from the metal center while the other remains firmly bound, a behaviour which has been found to increase the reactivity of catalysts when compared to the use of more traditional ligands.

Non-innocent ligand

Main article: Non-innocent ligand

Non-innocent ligands bond with metals in such a manner that the distribution of electron density between the metal center and ligand is unclear. Describing the bonding of non-innocent ligands often involves writing multiple resonance forms that have partial contributions to the overall state.

Common ligands

See also: Complex (chemistry) § Naming complexes

Virtually every molecule and every ion can serve as a ligand for (or "coordinate to") metals. Monodentate ligands include virtually all anions and all simple Lewis bases. Thus, the halides and pseudohalides are important anionic ligands whereas ammonia, carbon monoxide, and water are particularly common charge-neutral ligands. Simple organic species are also very common, be they anionic (RO⁻ and RCO⁻
₂) or neutral (R₂O, R₂S, R_3−xNH_x, and R₃P). The steric properties of some ligands are evaluated in terms of their cone angles.

Beyond the classical Lewis bases and anions, all unsaturated molecules are also ligands, utilizing their pi electrons in forming the coordinate bond. Also, metals can bind to the σ bonds in for example silanes, hydrocarbons, and dihydrogen (see also: Agostic interaction).

In complexes of non-innocent ligands, the ligand is bonded to metals via conventional bonds, but the ligand is also redox-active.

Examples of common ligands (by field strength)

In the following table the ligands are sorted by field strength (weak field ligands first):

Ligand	formula (bonding atom(s) in bold)	Charge	Most common denticity	Remark(s)
Iodide (iodo)	I−	monoanionic	monodentate
Bromide (bromido)	Br−	monoanionic	monodentate
Sulfide (thio or less commonly "bridging thiolate")	S2−	dianionic	monodentate (M=S), or bidentate bridging (M−S−M')
Thiocyanate (S-thiocyanato)	S−CN−	monoanionic	monodentate	ambidentate (see also isothiocyanate, below)
Chloride (chlorido)	Cl−	monoanionic	monodentate	also found bridging
Nitrate (nitrato)	O−NO− 2	monoanionic	monodentate
Azide (azido)	N−N− 2	monoanionic	monodentate	Very Toxic
Fluoride (fluoro)	F−	monoanionic	monodentate
Hydroxide (hydroxido)	O−H−	monoanionic	monodentate	often found as a bridging ligand
Oxalate (oxalato)	[O−CO−CO−O]2−	dianionic	bidentate
Water (aqua)	O−H2	neutral	monodentate
Nitrite (nitrito)	O−N−O−	monoanionic	monodentate	ambidentate (see also nitro)
Isothiocyanate (isothiocyanato)	N=C=S−	monoanionic	monodentate	ambidentate (see also thiocyanate, above)
Acetonitrile (acetonitrilo)	CH3CN	neutral	monodentate
Pyridine (py)	C5H5N	neutral	monodentate
Ammonia (ammine or less commonly "ammino")	NH3	neutral	monodentate
Ethylenediamine (en)	NH2−CH2−CH2−NH2	neutral	bidentate
2,2'-Bipyridine (bipy)	NC5H4−C5H4N	neutral	bidentate	easily reduced to its (radical) anion or even to its dianion
1,10-Phenanthroline (phen)	C12H8N2	neutral	bidentate
Nitrite (nitro)	N−O− 2	monoanionic	monodentate	ambidentate (see also nitrito)
Triphenylphosphine	P−(C6H5)3	neutral	monodentate
Cyanide (cyano)	C≡N− N≡C−	monoanionic	monodentate	can bridge between metals (both metals bound to C, or one to C and one to N)
Carbon monoxide (carbonyl)	–CO, others	neutral	monodentate	can bridge between metals (both metals bound to C)

The entries in the table are sorted by field strength, binding through the stated atom (i.e. as a terminal ligand). The 'strength' of the ligand changes when the ligand binds in an alternative binding mode (e.g., when it bridges between metals) or when the conformation of the ligand gets distorted (e.g., a linear ligand that is forced through steric interactions to bind in a nonlinear fashion).

Other generally encountered ligands (alphabetical)

In this table other common ligands are listed in alphabetical order.

Ligand	Formula (bonding atom(s) in bold)	Charge	Most common denticity	Remark(s)
Acetylacetonate (acac)	CH3−CO−CH2−CO−CH3	monoanionic	bidentate	In general bidentate, bound through both oxygens, but sometimes bound through the central carbon only, see also analogous ketimine analogues
Alkenes	R2C=CR2	neutral		compounds with a C−C double bond
Aminopolycarboxylic acids (APCAs)
BAPTA (1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid)
Benzene	C6H6	neutral		and other arenes
1,2-Bis(diphenylphosphino)ethane (dppe)	(C6H5)2P−C2H4−P(C6H5)2	neutral	bidentate
1,1-Bis(diphenylphosphino)methane (dppm)	(C6H5)2P−CH2−P(C6H5)2	neutral		Can bond to two metal atoms at once, forming dimers
Corroles			tetradentate
Crown ethers		neutral		primarily for alkali and alkaline earth metal cations
2,2,2-cryptand			hexadentate	primarily for alkali and alkaline earth metal cations
Cryptates		neutral
Cyclopentadienyl (Cp)	C 5H− 5	monoanionic		Although monoanionic, by the nature of its occupied molecular orbitals, it is capable of acting as a tridentate ligand.
Diethylenetriamine (dien)	C4H13N3	neutral	tridentate	related to TACN, but not constrained to facial complexation
Dimethylglyoximate (dmgH−)		monoanionic
1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA)
Diethylenetriaminepentaacetic acid (DTPA) (pentetic acid)
Ethylenediaminetetraacetic acid (EDTA) (edta4−)	(−OOC−CH2)2N−C2H4−N(CH2-COO−)2	tetraanionic	hexadentate
Ethylenediaminetriacetate	−OOC−CH2NH−C2H4−N(CH2-COO−)2	trianionic	pentadentate
Ethyleneglycolbis(oxyethylenenitrilo)tetraacetate (egta4−)	(−OOC−CH2)2N−C2H4−O−C2H4−O−C2H4−N(CH2−COO−)2	tetraanionic	octodentate
Fura-2
Glycinate (glycinato)	NH2CH2COO−	monoanionic	bidentate	other α-amino acid anions are comparable (but chiral)
Heme		dianionic	tetradentate	macrocyclic ligand
Iminodiacetic acid (IDA)			tridentate	Used extensively to make radiotracers for scintigraphy by complexing the metastable radionuclide technetium-99m. For example, in cholescintigraphy, HIDA, BrIDA, PIPIDA, and DISIDA are used
Nicotianamine				Ubiquitous in higher plants
Nitrosyl	NO+	cationic		bent (1e−) and linear (3e−) bonding mode
Nitrilotriacetic acid (NTA)
Oxo	O2−	dianion	monodentate	sometimes bridging
Pyrazine	N2C4H4	neutral	ditopic	sometimes bridging
Scorpionate ligand			tridentate
Sulfite	O−SO2− 2 S−O2− 3	monoanionic	monodentate	ambidentate
2,2';6',2″-Terpyridine (terpy)	NC5H4−C5H3N−C5H4N	neutral	tridentate	meridional bonding only
Triazacyclononane (tacn)	(C2H4)3(NR)3	neutral	tridentate	macrocyclic ligand see also the N,N′,N″-trimethylated analogue
Tricyclohexylphosphine	P(C6H11)3 or PCy3	neutral	monodentate
Triethylenetetramine (trien)	C6H18N4	neutral	tetradentate
Trimethylphosphine	P(CH3)3	neutral	monodentate
Tris(o-tolyl)phosphine	P(o-tolyl)3	neutral	monodentate
Tris(2-aminoethyl)amine (tren)	(NH2CH2CH2)3N	neutral	tetradentate
Tris(2-diphenylphosphineethyl)amine (np3)		neutral	tetradentate
Tropylium	C 7H+ 7	cationic
Carbon dioxide	–CO2, others	neutral		see metal carbon dioxide complex
Phosphorus trifluoride (trifluorophosphorus)	–PF3	neutral

Ligand exchange

A ligand exchange (also ligand substitution) is a type of chemical reaction in which a ligand in a compound is replaced by another. One type of pathway for substitution is the ligand dependent pathway. In organometallic chemistry this can take place via associative substitution or by dissociative substitution.

Ligand–protein binding database

BioLiP is a comprehensive ligand–protein interaction database, with the 3D structure of the ligand–protein interactions taken from the Protein Data Bank. MANORAA is a webserver for analyzing conserved and differential molecular interaction of the ligand in complex with protein structure homologs from the Protein Data Bank. It provides the linkage to protein targets such as its location in the biochemical pathways, SNPs and protein/RNA baseline expression in target organ.