Theoretical astronomy

From Wikipedia, the free encyclopedia

Theoretical astronomy is the use of the analytical models of physics and chemistry to describe astronomical objects and astronomical phenomena. 

 

Ptolemy's Almagest, although a brilliant treatise on theoretical astronomy combined with a practical handbook for computation, nevertheless includes many compromises to reconcile discordant observations. Theoretical astronomy is usually assumed to have begun with Johannes Kepler (1571–1630), and Kepler's laws. It is co-equal with observation. The general history of astronomy deals with the history of the descriptive and theoretical astronomy of the Solar System, from the late sixteenth century to the end of the nineteenth century. The major categories of works on the history of modern astronomy include general histories, national and institutional histories, instrumentation, descriptive astronomy, theoretical astronomy, positional astronomy, and astrophysics. Astronomy was early to adopt computational techniques to model stellar and galactic formation and celestial mechanics. From the point of view of theoretical astronomy, not only must the mathematical expression be reasonably accurate but it should preferably exist in a form which is amenable to further mathematical analysis when used in specific problems. Most of theoretical astronomy uses Newtonian theory of gravitation, considering that the effects of general relativity are weak for most celestial objects. The obvious fact is that theoretical astronomy cannot (and does not try to) predict the position, size and temperature of every star in the heavens. Theoretical astronomy by and large has concentrated upon analyzing the apparently complex but periodic motions of celestial objects.

Integrating astronomy and physics

"Contrary to the belief generally held by laboratory physicists, astronomy has contributed to the growth of our understanding of physics." Physics has helped in the elucidation of astronomical phenomena, and astronomy has helped in the elucidation of physical phenomena:

1. Discovery of the law of gravitation came from the information provided by the motion of the Moon and the planets,
2. Viability of nuclear fusion as demonstrated in the Sun and stars and yet to be reproduced on earth in a controlled form.

Integrating astronomy with physics involves

Physical interaction	Astronomical phenomena
Electromagnetism:	observation using the electromagnetic spectrum
black body radiation	stellar radiation
synchrotron radiation	radio and X-ray sources
inverse-Compton scattering	astronomical X-ray sources
acceleration of charged particles	pulsars and cosmic rays
absorption/scattering	interstellar dust
Strong and weak interaction:	nucleosynthesis in stars
	cosmic rays
	supernovae
	primeval universe
Gravity:	motion of planets, satellites and binary stars, stellar structure and evolution, N-body motions in clusters of stars and galaxies, black holes, and the expanding universe.

The aim of astronomy is to understand the physics and chemistry from the laboratory that is behind cosmic events so as to enrich our understanding of the cosmos and of these sciences as well.

Integrating astronomy and chemistry

Astrochemistry, the overlap of the disciplines of astronomy and chemistry, is the study of the abundance and reactions of chemical elements and molecules in space, and their interaction with radiation. The formation, atomic and chemical composition, evolution and fate of molecular gas clouds, is of special interest because it is from these clouds that solar systems form.

Infrared astronomy, for example, has revealed that the interstellar medium contains a suite of complex gas-phase carbon compounds called aromatic hydrocarbons, often abbreviated (PAHs or PACs). These molecules composed primarily of fused rings of carbon (either neutral or in an ionized state) are said to be the most common class of carbon compound in the galaxy. They are also the most common class of carbon molecule in meteorites and in cometary and asteroidal dust (cosmic dust). These compounds, as well as the amino acids, nucleobases, and many other compounds in meteorites, carry deuterium (²H) and isotopes of carbon, nitrogen, and oxygen that are very rare on earth, attesting to their extraterrestrial origin. The PAHs are thought to form in hot circumstellar environments (around dying carbon rich red giant stars). 

The sparseness of interstellar and interplanetary space results in some unusual chemistry, since symmetry-forbidden reactions cannot occur except on the longest of timescales. For this reason, molecules and molecular ions which are unstable on earth can be highly abundant in space, for example the H₃⁺ ion. Astrochemistry overlaps with astrophysics and nuclear physics in characterizing the nuclear reactions which occur in stars, the consequences for stellar evolution, as well as stellar 'generations'. Indeed, the nuclear reactions in stars produce every naturally occurring chemical element. As the stellar 'generations' advance, the mass of the newly formed elements increases. A first-generation star uses elemental hydrogen (H) as a fuel source and produces helium (He). Hydrogen is the most abundant element, and it is the basic building block for all other elements as its nucleus has only one proton. Gravitational pull toward the center of a star creates massive amounts of heat and pressure, which cause nuclear fusion. Through this process of merging nuclear mass, heavier elements are formed. Lithium, carbon, nitrogen and oxygen are examples of elements that form in stellar fusion. After many stellar generations, very heavy elements are formed (e.g. iron and lead).

Tools of theoretical astronomy

Theoretical astronomers use a wide variety of tools which include analytical models (for example, polytropes to approximate the behaviors of a star) and computational numerical simulations. Each has some advantages. Analytical models of a process are generally better for giving insight into the heart of what is going on. Numerical models can reveal the existence of phenomena and effects that would otherwise not be seen.

Astronomy theorists endeavor to create theoretical models and figure out the observational consequences of those models. This helps observers look for data that can refute a model or help in choosing between several alternate or conflicting models. 

Theorists also try to generate or modify models to take into account new data. Consistent with the general scientific approach, in the case of an inconsistency, the general tendency is to try to make minimal modifications to the model to fit the data. In some cases, a large amount of inconsistent data over time may lead to total abandonment of a model.

Topics of theoretical astronomy

Topics studied by theoretical astronomers include

1. stellar dynamics and evolution;
2. galaxy formation;
3. large-scale structure of matter in the Universe;
4. origin of cosmic rays;
5. general relativity and physical cosmology, including string cosmology and astroparticle physics.

Astrophysical relativity serves as a tool to gauge the properties of large scale structures for which gravitation plays a significant role in physical phenomena investigated and as the basis for black hole (astro)physics and the study of gravitational waves.

Astronomical models

Some widely accepted and studied theories and models in astronomy, now included in the Lambda-CDM model are the Big Bang, Cosmic inflation, dark matter, and fundamental theories of physics.

A few examples of this process: 

Physical process	Experimental tool	Theoretical model	Explains/predicts
Gravitation	Radio telescopes	Self-gravitating system	Emergence of a star system
Nuclear fusion	Spectroscopy	Stellar evolution	How the stars shine and how metals formed
The Big Bang	Hubble Space Telescope, COBE	Expanding universe	Age of the Universe
Quantum fluctuations		Cosmic inflation	Flatness problem
Gravitational collapse	X-ray astronomy	General relativity	Black holes at the center of Andromeda Galaxy
CNO cycle in stars

Leading topics in theoretical astronomy

Dark matter and dark energy are the current leading topics in astronomy, as their discovery and controversy originated during the study of the galaxies.

Theoretical astrophysics

Of the topics approached with the tools of theoretical physics, particular consideration is often given to stellar photospheres, stellar atmospheres, the solar atmosphere, planetary atmospheres, gaseous nebulae, nonstationary stars, and the interstellar medium. Special attention is given to the internal structure of stars.

Weak equivalence principle

The observation of a neutrino burst within 3 h of the associated optical burst from Supernova 1987A in the Large Magellanic Cloud (LMC) gave theoretical astrophysicists an opportunity to test that neutrinos and photons follow the same trajectories in the gravitational field of the galaxy.

Thermodynamics for stationary black holes

A general form of the first law of thermodynamics for stationary black holes can be derived from the microcanonical functional integral for the gravitational field. The boundary data

1. the gravitational field as described with a micocanonical system in a spatially finite region and
2. the density of states expressed formally as a functional integral over Lorentzian metrics and as a functional of the geometrical boundary data that are fixed in the corresponding action,

are the thermodynamical extensive variables, including the energy and angular momentum of the system. For the simpler case of nonrelativistic mechanics as is often observed in astrophysical phenomena associated with a black hole event horizon, the density of states can be expressed as a real-time functional integral and subsequently used to deduce Feynman's imaginary-time functional integral for the canonical partition function.

Theoretical astrochemistry

Reaction equations and large reaction networks are an important tool in theoretical astrochemistry, especially as applied to the gas-grain chemistry of the interstellar medium. Theoretical astrochemistry offers the prospect of being able to place constraints on the inventory of organics for exogenous delivery to the early Earth.

Interstellar organics

"An important goal for theoretical astrochemistry is to elucidate which organics are of true interstellar origin, and to identify possible interstellar precursors and reaction pathways for those molecules which are the result of aqueous alterations." One of the ways this goal can be achieved is through the study of carbonaceous material as found in some meteorites. Carbonaceous chondrites (such as C1 and C2) include organic compounds such as amines and amides; alcohols, aldehydes, and ketones; aliphatic and aromatic hydrocarbons; sulfonic and phosphonic acids; amino, hydroxycarboxylic, and carboxylic acids; purines and pyrimidines; and kerogen-type material. The organic inventories of primitive meteorites display large and variable enrichments in deuterium, carbon-13 (¹³C), and nitrogen-15 (¹⁵N), which is indicative of their retention of an interstellar heritage.

Chemistry in cometary comae

The chemical composition of comets should reflect both the conditions in the outer solar nebula some 4.5 × 10⁹ ayr, and the nature of the natal interstellar cloud from which the Solar system was formed. While comets retain a strong signature of their ultimate interstellar origins, significant processing must have occurred in the protosolar nebula. Early models of coma chemistry showed that reactions can occur rapidly in the inner coma, where the most important reactions are proton transfer reactions. Such reactions can potentially cycle deuterium between the different coma molecules, altering the initial D/H ratios released from the nuclear ice, and necessitating the construction of accurate models of cometary deuterium chemistry, so that gas-phase coma observations can be safely extrapolated to give nuclear D/H ratios.

Theoretical chemical astronomy

While the lines of conceptual understanding between theoretical astrochemistry and theoretical chemical astronomy often become blurred so that the goals and tools are the same, there are subtle differences between the two sciences. Theoretical chemistry as applied to astronomy seeks to find new ways to observe chemicals in celestial objects, for example. This often leads to theoretical astrochemistry having to seek new ways to describe or explain those same observations.

Astronomical spectroscopy

The new era of chemical astronomy had to await the clear enunciation of the chemical principles of spectroscopy and the applicable theory.

Chemistry of dust condensation

Supernova radioactivity dominates light curves and the chemistry of dust condensation is also dominated by radioactivity. Dust is usually either carbon or oxides depending on which is more abundant, but Compton electrons dissociate the CO molecule in about one month. The new chemical astronomy of supernova solids depends on the supernova radioactivity:

1. The radiogenesis of ⁴⁴Ca from ⁴⁴Ti decay after carbon condensation establishes their supernova source,
2. Their opacity suffices to shift emission lines blueward after 500 d and emits significant infrared luminosity,
3. Parallel kinetic rates determine trace isotopes in meteoritic supernova graphites,
4. The chemistry is kinetic rather than due to thermal equilibrium and
5. Is made possible by radiodeactivation of the CO trap for carbon.

Theoretical physical astronomy

Like theoretical chemical astronomy, the lines of conceptual understanding between theoretical astrophysics and theoretical physical astronomy are often blurred, but, again, there are subtle differences between these two sciences. Theoretical physics as applied to astronomy seeks to find new ways to observe physical phenomena in celestial objects and what to look for, for example. This often leads to theoretical astrophysics having to seek new ways to describe or explain those same observations, with hopefully a convergence to improve our understanding of the local environment of Earth and the physical Universe.

Weak interaction and nuclear double beta decay

Nuclear matrix elements of relevant operators as extracted from data and from a shell-model and theoretical approximations both for the two-neutrino and neutrinoless modes of decay are used to explain the weak interaction and nuclear structure aspects of nuclear double beta decay.

Neutron-rich isotopes

New neutron-rich isotopes, ³⁴Ne, ³⁷Na, and ⁴³Si have been produced unambiguously for the first time, and convincing evidence for the particle instability of three others, ³³Ne, ³⁶Na, and ³⁹Mg has been obtained. These experimental findings compare with recent theoretical predictions.

Theory of astronomical time keeping

Until recently all the time units that appear natural to us are caused by astronomical phenomena:

1. Earth's orbit around the Sun => the year, and the seasons,
2. Moon's orbit around the Earth => the month,
3. Earth's rotation and the succession of brightness and darkness => the day (and night).

High precision appears problematic:

1. Amibiguities arise in the exact definition of a rotation or revolution,
2. Some astronomical processes are uneven and irregular, such as the noncommensurability of year, month, and day,
3. There are a multitude of time scales and calendars to solve the first two problems.

Some of these time scales are sidereal time, solar time, and universal time.

Atomic time

Historical accuracy of atomic clocks from NIST.

 

From the Systeme Internationale (SI) comes the second as defined by the duration of 9 192 631 770 cycles of a particular hyperfine structure transition in the ground state of caesium-133 (¹³³Cs). For practical usability a device is required that attempts to produce the SI second (s) such as an atomic clock. But not all such clocks agree. The weighted mean of many clocks distributed over the whole Earth defines the Temps Atomique International; i.e., the Atomic Time TAI. From the General theory of relativity the time measured depends on the altitude on earth and the spatial velocity of the clock so that TAI refers to a location on sea level that rotates with the Earth.

Ephemeris time

Since the Earth's rotation is irregular, any time scale derived from it such as Greenwich Mean Time led to recurring problems in predicting the Ephemerides for the positions of the Moon, Sun, planets and their natural satellites. In 1976 the International Astronomical Union (IAU) resolved that the theoretical basis for ephemeris time (ET) was wholly non-relativistic, and therefore, beginning in 1984 ephemeris time would be replaced by two further time scales with allowance for relativistic corrections. Their names, assigned in 1979, emphasized their dynamical nature or origin, Barycentric Dynamical Time (TDB) and Terrestrial Dynamical Time (TDT). Both were defined for continuity with ET and were based on what had become the standard SI second, which in turn had been derived from the measured second of ET.

During the period 1991–2006, the TDB and TDT time scales were both redefined and replaced, owing to difficulties or inconsistencies in their original definitions. The current fundamental relativistic time scales are Geocentric Coordinate Time (TCG) and Barycentric Coordinate Time (TCB). Both of these have rates that are based on the SI second in respective reference frames (and hypothetically outside the relevant gravity well), but due to relativistic effects, their rates would appear slightly faster when observed at the Earth's surface, and therefore diverge from local Earth-based time scales using the SI second at the Earth's surface.

The currently defined IAU time scales also include Terrestrial Time (TT) (replacing TDT, and now defined as a re-scaling of TCG, chosen to give TT a rate that matches the SI second when observed at the Earth's surface), and a redefined Barycentric Dynamical Time (TDB), a re-scaling of TCB to give TDB a rate that matches the SI second at the Earth's surface.

Extraterrestrial time-keeping

Stellar dynamical time scale

For a star, the dynamical time scale is defined as the time that would be taken for a test particle released at the surface to fall under the star's potential to the centre point, if pressure forces were negligible. In other words, the dynamical time scale measures the amount of time it would take a certain star to collapse in the absence of any internal pressure. By appropriate manipulation of the equations of stellar structure this can be found to be

${\displaystyle \tau _{dynamical}\simeq {\frac {R}{v}}={\sqrt {\frac {R^{3}}{2GM}}}\sim 1/{\sqrt {G\rho }}}$

where R is the radius of the star, G is the gravitational constant, M is the mass of the star and v is the escape velocity. As an example, the Sun dynamical time scale is approximately 1133 seconds. Note that the actual time it would take a star like the Sun to collapse is greater because internal pressure is present. 

The 'fundamental' oscillatory mode of a star will be at approximately the dynamical time scale. Oscillations at this frequency are seen in Cepheid variables.

Theory of astronomical navigation

On earth

The basic characteristics of applied astronomical navigation are

1. usable in all areas of sailing around the earth,
2. applicable autonomously (does not depend on others – persons or states) and passively (does not emit energy),
3. conditional usage via optical visibility (of horizon and celestial bodies), or state of cloudiness,
4. precisional measurement, sextant is 0.1', altitude and position is between 1.5' and 3.0'.
5. temporal determination takes a couple of minutes (using the most modern equipment) and ≤ 30 min (using classical equipment).

The superiority of satellite navigation systems to astronomical navigation are currently undeniable, especially with the development and use of GPS/NAVSTAR. This global satellite system

1. enables automated three-dimensional positioning at any moment,
2. automatically determines position continuously (every second or even more often),
3. determines position independent of weather conditions (visibility and cloudiness),
4. determines position in real time to a few meters (two carrying frequencies) and 100 m (modest commercial receivers), which is two to three orders of magnitude better than by astronomical observation,
5. is simple even without expert knowledge,
6. is relatively cheap, comparable to equipment for astronomical navigation, and
7. allows incorporation into integrated and automated systems of control and ship steering. The use of astronomical or celestial navigation is disappearing from the surface and beneath or above the surface of the earth.

Geodetic astronomy is the application of astronomical methods into networks and technical projects of geodesy for

• apparent places of stars, and their proper motions
• precise astronomical navigation
• astro-geodetic geoid determination and
• modelling the rock densities of the topography and of geological layers in the subsurface
• Satellite geodesy using the stellar background (see also astrometry and cosmic triangulation)
• Monitoring of the Earth rotation and polar wandering
• Contribution to the time system of physics and geosciences

Astronomical algorithms are the algorithms used to calculate ephemerides, calendars, and positions (as in celestial navigation or satellite navigation).

Many astronomical and navigational computations use the Figure of the Earth as a surface representing the earth. 

The International Earth Rotation and Reference Systems Service (IERS), formerly the International Earth Rotation Service, is the body responsible for maintaining global time and reference frame standards, notably through its Earth Orientation Parameter (EOP) and International Celestial Reference System (ICRS) groups.

Deep space

The Deep Space Network, or DSN, is an international network of large antennas and communication facilities that supports interplanetary spacecraft missions, and radio and radar astronomy observations for the exploration of the solar system and the universe. The network also supports selected Earth-orbiting missions. DSN is part of the NASA Jet Propulsion Laboratory (JPL).

Aboard an exploratory vehicle

An observer becomes a deep space explorer upon escaping Earth's orbit. While the Deep Space Network maintains communication and enables data download from an exploratory vessel, any local probing performed by sensors or active systems aboard usually require astronomical navigation, since the enclosing network of satellites to ensure accurate positioning is absent.

Mass versus weight

From Wikipedia, the free encyclopedia

In common usage, the mass of an object is often referred to as its weight, though these are in fact different concepts and quantities. In scientific contexts, mass is the amount of "matter" in an object (though "matter" may be difficult to define), whereas weight is the force exerted on an object by gravity. In other words, an object with a mass of 1.0 kilogram weighs approximately 9.81 newtons on the surface of the Earth, which is its mass multiplied by the gravitational field strength. The object's weight is less on Mars, where gravity is weaker, and more on Saturn, and very small in space when far from any significant source of gravity, but it always has the same mass. 

 

Objects on the surface of the Earth have weight, although sometimes this weight is difficult to measure. An example is a small object floating in water, which does not appear to have weight since it is buoyed by the water; but it is found to have its usual weight when it is added to water in a container which is entirely supported by and weighed on a scale. Thus, the "weightless object" floating in water actually transfers its weight to the bottom of the container (where the pressure increases). Similarly, a balloon has mass but may appear to have no weight or even negative weight, due to buoyancy in air. However the weight of the balloon and the gas inside it has merely been transferred to a large area of the Earth's surface, making the weight difficult to measure. The weight of a flying airplane is similarly distributed to the ground, but does not disappear. If the airplane is in level flight, the same weight-force is distributed to the surface of the Earth as when the plane was on the runway, but spread over a larger area.

A better scientific definition of mass is its description as being composed of inertia, which is the resistance of an object being accelerated when acted on by an external force. Gravitational "weight" is the force created when a mass is acted upon by a gravitational field and the object is not allowed to free-fall, but is supported or retarded by a mechanical force, such as the surface of a planet. Such a force constitutes weight. This force can be added to by any other kind of force.

While the weight of an object varies in proportion to the strength of the gravitational field, its mass is constant (ignoring relativistic effects) as long as no energy or matter is added to the object. For example, although a satellite in orbit (essentially a free-fall) is "weightless", it still retains its mass and inertia. Accordingly, even in orbit, an astronaut trying to accelerate the satellite in any direction is still required to exert force, and needs to exert ten times as much force to accelerate a 10‑ton satellite at the same rate as one with a mass of only 1 ton.

Overview

Matter's mass strongly influences many familiar kinetic properties.

 

Mass is (among other properties) an inertial property; that is, the tendency of an object to remain at constant velocity unless acted upon by an outside force. Under Sir Isaac Newton's 332-year-old laws of motion and an important formula that sprang from his work, F = ma, an object with a mass, m, of one kilogram accelerates, a, at one meter per second per second (about one-tenth the acceleration due to earth's gravity)^[4] when acted upon by a force, F, of one newton. 

Inertia is seen when a bowling ball is pushed horizontally on a level, smooth surface, and continues in horizontal motion. This is quite distinct from its weight, which is the downwards gravitational force of the bowling ball one must counter when holding it off the floor. The weight of the bowling ball on the Moon would be one-sixth of that on the Earth, although its mass remains unchanged. Consequently, whenever the physics of recoil kinetics (mass, velocity, inertia, inelastic and elastic collisions) dominate and the influence of gravity is a negligible factor, the behavior of objects remains consistent even where gravity is relatively weak. For instance, billiard balls on a billiard table would scatter and recoil with the same speeds and energies after a break shot on the Moon as on Earth; they would, however, drop into the pockets much more slowly.

In the physical sciences, the terms "mass" and "weight" are rigidly defined as separate measures, as they are different physical properties. In everyday use, as all everyday objects have both mass and weight and one is almost exactly proportional to the other, "weight" often serves to describe both properties, its meaning being dependent upon context. For example, in retail commerce, the "net weight" of products actually refers to mass, and is expressed in mass units such as grams or ounces (see also Pound: Use in commerce). Conversely, the load index rating on automobile tires, which specifies the maximum structural load for a tire in kilograms, refers to weight; that is, the force due to gravity. Before the late 20th century, the distinction between the two was not strictly applied in technical writing, so that expressions such as "molecular weight" (for molecular mass) are still seen.

Because mass and weight are separate quantities, they have different units of measure. In the International System of Units (SI), the kilogram is the basic unit of mass, and the newton is the basic unit of force. The non-SI kilogram-force is also a unit of force typically used in the measure of weight. Similarly, the avoirdupois pound, used in both the Imperial system and U.S. customary units, is a unit of mass, and its related unit of force is the pound-force.

Converting units of mass to equivalent forces on Earth

Gravity anomalies covering the Southern Ocean are shown here in false-color relief. This image has been normalized to remove variation due to differences in latitude.

 

When an object's weight (its gravitational force) is expressed in "kilograms", this actually refers to the kilogram-force (kgf or kg-f), also known as the kilopond (kp), which is a non-SI unit of force. All objects on the Earth's surface are subject to a gravitational acceleration of approximately 9.8 m/s². The General Conference on Weights and Measures fixed the value of standard gravity at precisely 9.80665 m/s² so that disciplines such as metrology would have a standard value for converting units of defined mass into defined forces and pressures. Thus the kilogram-force is defined as precisely 9.80665 newtons. In reality, gravitational acceleration (symbol: g) varies slightly with latitude, elevation and subsurface density; these variations are typically only a few tenths of a percent. See also Gravimetry. 

Engineers and scientists understand the distinctions between mass, force, and weight. Engineers in disciplines involving weight loading (force on a structure due to gravity), such as structural engineering, convert the mass of objects like concrete and automobiles (expressed in kilograms) to a force in newtons (by multiplying by some factor around 9.8; 2 significant figures is usually sufficient for such calculations) to derive the load of the object. Material properties like elastic modulus are measured and published in terms of the newton and pascal (a unit of pressure related to the newton).

Buoyancy and weight

Regardless of the fluid in which an object is immersed (gas or liquid), the buoyant force on an object is equal to the weight of the fluid it displaces.

 

A hot air balloon when it has neutral buoyancy has no weight for the men to support but still retains great inertia due to its mass.

 

Usually, the relationship between mass and weight on Earth is highly proportional; objects that are a hundred times more massive than a one-liter bottle of soda almost always weigh a hundred times more—approximately 1,000 newtons, which is the weight one would expect on Earth from an object with a mass slightly greater than 100 kilograms. Yet, this is not always the case and there are familiar objects that violate this mass / weight proportionality. 

A common helium-filled toy balloon is something familiar to many. When such a balloon is fully filled with helium, it has buoyancy—a force that opposes gravity. When a toy balloon becomes partially deflated, it often becomes neutrally buoyant and can float about the house a meter or two off the floor. In such a state, there are moments when the balloon is neither rising nor falling and—in the sense that a scale placed under it has no force applied to it—is, in a sense perfectly weightless (actually as noted below, weight has merely been redistributed along the Earth's surface so it cannot be measured). Though the rubber comprising the balloon has a mass of only a few grams, which might be almost unnoticeable, the rubber still retains all its mass when inflated.

Again, unlike the effect that low-gravity environments have on weight, buoyancy does not make a portion of an object's weight vanish; the missing weight is instead being borne by the ground, which leaves less force (weight) being applied to any scale theoretically placed underneath the object in question (though one may perhaps have some trouble with the practical aspects of accurately weighing something individually in that condition). If one were however to weigh a small wading pool that someone then entered and began floating in, they would find that the full weight of the person was being borne by the pool and, ultimately, the scale underneath the pool. Whereas a buoyant object (on a properly working scale for weighing buoyant objects) would weigh less, the object/fluid system becomes heavier by the value of object's full mass once the object is added. Since air is a fluid, this principle applies to object/air systems as well; large volumes of air—and ultimately the ground—supports the weight a body loses through mid-air buoyancy. 

The effects of buoyancy do not just affect balloons; both liquids and gases are fluids in the physical sciences, and when all macro‑size objects larger than dust particles are immersed in fluids on Earth, they have some degree of buoyancy. In the case of either a swimmer floating in a pool or a balloon floating in air, buoyancy can fully counter the gravitational weight of the object being weighed, for a weighing device in the pool. However, as noted, an object supported by a fluid is fundamentally no different from an object supported by a sling or cable—the weight has merely been transferred to another location, not made to disappear.

The mass of "weightless" (neutrally buoyant) balloons can be better appreciated with much larger hot air balloons. Although no effort is required to counter their weight when they are hovering over the ground (when they can often be within one hundred newtons of zero weight), the inertia associated with their appreciable mass of several hundred kilograms or more can knock fully grown men off their feet when the balloon's basket is moving horizontally over the ground.

Buoyancy and the resultant reduction in the downward force of objects being weighed underlies Archimedes' principle, which states that the buoyancy force is equal to the weight of the fluid that the object displaces. If this fluid is air, the force may be small.

Buoyancy effects of air on measurement

Normally, the effect of air buoyancy on objects of normal density is too small to be of any consequence in day-to-day activities. For instance, buoyancy's diminishing effect upon one's body weight (a relatively low-density object) is ​¹⁄₈₆₀ that of gravity (for pure water it is about ​¹⁄₇₇₀ that of gravity). Furthermore, variations in barometric pressure rarely affect a person's weight more than ±1 part in 30,000. However, in metrology (the science of measurement), the precision mass standards for calibrating laboratory scales and balances are manufactured with such accuracy that air density is accounted for to compensate for buoyancy effects. Given the extremely high cost of platinum-iridium mass standards like the International Prototype Kilogram (the mass standard in France that defined the magnitude of the kilogram), high-quality "working" standards are made of special stainless steel alloys with densities of about 8,000 kg/m³, which occupy greater volume than those made of platinum-iridium, which have a density of about 21,550 kg/m³. For convenience, a standard value of buoyancy relative to stainless steel was developed for metrology work and this results in the term "conventional mass". Conventional mass is defined as follows: "For a mass at 20 °C, ‘conventional mass’ is the mass of a reference standard of density 8,000 kg/m³ which it balances in air with a density of 1.2 kg/m³." The effect is a small one, 150 ppm for stainless steel mass standards, but the appropriate corrections are made during the manufacture of all precision mass standards so they have the true labeled mass. 

Whenever a high-precision scale (or balance) in routine laboratory use is calibrated using stainless steel standards, the scale is actually being calibrated to conventional mass; that is, true mass minus 150 ppm of buoyancy. Since objects with precisely the same mass but with different densities displace different volumes and therefore have different buoyancies and weights, any object measured on this scale (compared to a stainless steel mass standard) has its conventional mass measured; that is, its true mass minus an unknown degree of buoyancy. In high-accuracy work, the volume of the article can be measured to mathematically null the effect of buoyancy.

Types of scales and what they measure

A balance-type weighing scale: Unaffected by the strength of gravity.

 

Load-cell based bathroom scale: Affected by the strength of gravity.

 

When one stands on a balance-beam-type scale at a doctor’s office, they are having their mass measured directly. This is because balances ("dual-pan" mass comparators) compare the gravitational force exerted on the person on the platform with that on the sliding counterweights on the beams; gravity is the force-generating mechanism that allows the needle to diverge from the "balanced" (null) point. These balances could be moved from Earth's equator to the poles and give exactly the same measurement, i.e. they would not spuriously indicate that the doctor's patient became 0.3% heavier; they are immune to the gravity-countering centrifugal force due to Earth's rotation about its axis. But if you step onto spring-based or digital load cell-based scales (single-pan devices), you are having your weight (gravitational force) measured; and variations in the strength of the gravitational field affect the reading. In practice, when such scales are used in commerce or hospitals, they are often adjusted on-site and certified on that basis, so that the mass they measure, expressed in pounds or kilograms, is at the desired level of accuracy.

Use in commerce

In the United States of America the United States Department of Commerce, the Technology Administration, and the National Institute of Standards and Technology (NIST) have defined the use of mass and weight in the exchange of goods under the Uniform Laws and Regulations in the areas of legal metrology and engine fuel quality in NIST Handbook 130. 

NIST Handbook 130 states:

V. "Mass" and "Weight." [NOTE 1, See page 6]

The mass of an object is a measure of the object’s inertial property, or the amount of matter it contains. The weight of an object is a measure of the force exerted on the object by gravity, or the force needed to support it. The pull of gravity on the earth gives an object a downward acceleration of about 9.8 m/s². In trade and commerce and everyday use, the term "weight" is often used as a synonym for "mass." The "net mass" or "net weight" declared on a label indicates that the package contains a specific amount of commodity exclusive of wrapping materials. The use of the term "mass" is predominant throughout the world, and is becoming increasingly common in the United States. (Added 1993)

W. Use of the Terms "Mass" and "Weight." [NOTE 1, See page 6]

When used in this handbook, the term "weight" means "mass". The term "weight" appears when inch-pound units are cited, or when both inch-pound and SI units are included in a requirement. The terms "mass" or "masses" are used when only SI units are cited in a requirement. The following note appears where the term "weight" is first used in a law or regulation.

NOTE 1: When used in this law (or regulation), the term "weight" means "mass." (See paragraph V. and W. in Section I., Introduction, of NIST Handbook 130 for an explanation of these terms.) (Added 1993) 6"

U.S. federal law, which supersedes this handbook, also defines weight, particularly Net Weight, in terms of the avoirdupois pound or mass pound. From 21CFR101 Part 101.105 – Declaration of net quantity of contents when exempt:

(a) The principal display panel of a food in package form shall bear a declaration of the net quantity of contents. This shall be expressed in the terms of weight, measure, numerical count, or a combination of numerical count and weight or measure. The statement shall be in terms of fluid measure if the food is liquid, or in terms of weight if the food is solid, semisolid, or viscous, or a mixture of solid and liquid; except that such statement may be in terms of dry measure if the food is a fresh fruit, fresh vegetable, or other dry commodity that is customarily sold by dry measure. If there is a firmly established general consumer usage and trade custom of declaring the contents of a liquid by weight, or a solid, semisolid, or viscous product by fluid measure, it may be used. Whenever the Commissioner determines that an existing practice of declaring net quantity of contents by weight, measure, numerical count, or a combination in the case of a specific packaged food does not facilitate value comparisons by consumers and offers opportunity for consumer confusion, he will by regulation designate the appropriate term or terms to be used for such commodity.

(b)(1) Statements of weight shall be in terms of avoirdupois pound and ounce.

See also 21CFR201 Part 201.51 – "Declaration of net quantity of contents" for general labeling and prescription labeling requirements.

Gerard Verschuuren

From Wikipedia, the free encyclopedia

Gerard M. Verschuuren
Born	1946 Netherlands
Alma mater	Leiden University, Utrecht University, VU University Amsterdam
Spouse(s)	Trudy Doucette (m. 1983)
Scientific career
Fields	Biology, Human Genetics, Philosophy of Science, Philosophy of Biology, VBA, VB.NET and C#.NET
Doctoral advisor	Cornelis van Peursen
Other academic advisors	John Huizinga, Marius Jeuken

Gerard M. Verschuuren (pronounced Ver-SURE-rin) is a scientist, writer, speaker, and consultant, working at the interface of science, philosophy, and religion. He is a human biologist, specialized in human genetics, who also earned a doctorate in the philosophy of science, and studied and worked at universities in Europe and the United States. In 1994, he moved permanently to the United States, and lives now in the southern part of New Hampshire.

Studies and research

He began studying biology at Leiden University and specialized in human genetics at Utrecht University in the Netherlands, with a thesis on the statistical analysis of epigenetic variation in the Tellem skulls of Mali in comparison with the Kurumba tribe of Burkina Faso (former Upper Volta). After that, he became a participant of the six-member Human Adaptability Project team (led by professor John Huizinga, M.D.) of the former Institute of Human Biology at Utrecht University Medical School, as part of the International Biological Program, studying the population genetics and adaptation of savannah populations in sub-saharan Africa based on research among the Fali in Cameroun, among the Dogon in Mali, and among the Fulbe in Chad. 

Verschuuren also studied philosophy at Leiden University and wrote, under supervision of professor Marius Jeuken, a thesis on the impact of the Harvard philosopher and mathematician Alfred North Whitehead on research in biology. He further specialized in philosophy of science, in particular in philosophy of biology, at VU University Amsterdam. Verschuuren concluded his post-graduate studies with a doctoral thesis on the use of models in the sciences. In this work, he analyzes how all sciences use models, which are simplified replicas of the dissected original, made for research purposes by reducing the complexity of the original to a manageable model related to a soluble problem.

Verschuuren taught biology, biological anthropology, genetics, human genetics, statistics, philosophy, philosophy of biology, logic, and programming at Aloysius College, Utrecht University, the Dutch Open University, Merrimack College and Boston College. Currently, he focuses almost exclusively on writing, consulting, and on speaking engagements.

Educational work

Verschuuren became the leader of a team of textbook writers that developed three consecutive series of biology textbooks for high-schools and colleges under the names Biosfeer (1975–1983), Oculair (1984–1994), and Grondslagen van de Biologie(Foundations of Biology; 1985–present). He also became a member of the College Admission Test team for biology in the Netherlands (1976–1982).

For those specifically interested in the philosophy of biology, he wrote four textbooks: Investigating the Life Sciences: An Introduction to the Philosophy of Science (1986), Life Scientists: Their Convictions, Their Activities, and Their Values (1995), The Holism-Reductionism Debate - In Physics, Genetics, Biology, Neuroscience, Ecology, Sociology (2016), and Darwin's Philosophical Legacy - The Good and the Not-So-Good (2012). 

To reach fellow scientists as well, he started in cooperation with the professors Cornelis Van Peursen and Cornelis Schuyt, both of Leiden University, an overseeing editorial board for the development of 25 books on the philosophy of science for 25 specific fields, written by experts in those fields (1986–present), Nijhoff, Leiden, Series Philosophy of the Sciences. 

During the 1970s, Verschuuren wrote a weekly column on breaking biological topics in the Volkskrant daily. He was a member of the editorial board of the Dutch philosophical magazine Wijsgerig Perspectief, for which he wrote several of its articles, and a member of the editorial board of the Dutch-Flemish magazine Streven, for which he also wrote articles and book reviews (partial listing). All in all, he wrote many books and articles in Dutch on biological and philosophical issues (listing). 

In the 1980s, Verschuuren was an advisor to the Foundation Scientific Europe, which published a voluminous overview of research and technology in 20 European countries, entitled Scientific Europe (edited by Nigel Calder). From 1985 until 1994, he was the editor-in-chief of the Dutch magazine Natuurwetenschap en Techniek and publisher of the Dutch version of the Scientific American Library.

At the interface of science and religion

A practicing Catholic, Verschuuren is interested in the relationship between science and religion. It is his conviction that religion and science cannot be in conflict with each other and cannot be seen as a threat to each other, as long as both stay in their own territory, which prevents us from turning science into a pseudo-religion, or religion into a semi-science. Put in the words of Augustine of Hippo or Galileo Galilei, science reads the "Book of Nature" and religion reads the "Book of Scripture," for they both have the same Author, GOD. 

From this perspective, grounded in the tradition of Thomas Aquinas, he has written several books:

• Darwin's Philosophical Legacy - The Good and the Not-So-Good. There is hardly any university, college, or even high school left where they do not teach Darwinism—and rightly so. Yet, most of these places do more preaching than teaching. In what the author likes to call "The Good" parts of his legacy, he explores what Darwin's great contributions are to the study of evolution and to the theory of evolution. At the same time, he also delves into the areas where his thoughts were not so perfect or even wrong, especially in a philosophical sense—which he calls "The Not-So-Good" parts of his legacy. There are definitely two sides to Darwin's legacy and they need to be carefully balanced.
• God and Evolution - Science Meets Faith. This book discusses the issue of evolution and creation from a Catholic viewpoint, while avoiding the flaws and traps of the theory of Intelligent Design. It is a book for all who want to learn more about the science behind evolution in a way that does not detract from their deeply held faith but actually strengthens it. Lost in the raging debate about creation and evolution is the profound Catholic truth, affirmed by Popes and theologians from the earliest Church to today, that faith can never conflict with the truths of science—not even evolution.
• What Makes You Tick? - A New Paradigm for Neuroscience. In the first chapters, he argues that it is not molecules, DNA, or not even neurons that make you "tick." This is obviously contrasted with the current paradigm of neuroscience. The current paradigm of neuroscience—which he now calls the "old" paradigm—is too materialistic, too deterministic, and too reductionistic to do justice to the unique position of living human beings in the world. It calls for a more comprehensive paradigm!
• Of All That Is, Seen and Unseen - Life-Saving Answers to Life-Size Questions. This book belongs basically to the genre of apologetics and evangelization, thoroughly rooted in the Catholic tradition, with a mild philosophical touch based on the tradition of St. Thomas Aquinas. Because this book has basically a format of question-and-answer, the text is most engaging to the reader. Each chapter can be read independently and can be used as an outline for discussions and seminars.
• The Destiny of the Universe - In Pursuit of the Great Unknown. This book is not about astronomy, not even about science per se, but about the Great Unknown beyond and behind all that we can see through our telescopes and microscopes. Although, there is a lot of science in this book, at a simplified level, it is mainly a critical philosophical journey, starting in the world of science, but ultimately in pursuit of the Great Unknown that has become more and more known in the lives of so many people.
• It's All in the Genes! - Really?. A decade ago, the general estimate for the number of human genes was thought to be well over 100,000, but then turned out to be around 30,000 genes—which is only half again as many genes as a tiny roundworm needs to manufacture its utter simplicity. And human beings have only 300 unique genes not found in mice. No wonder that the president of Celera, a bio-corporation, said about this surprising finding "This tells me genes cannot possibly explain all of what makes us what we are." At least, we have a first indication here that genes are not as almighty as some want us to believe.
• Five Anti-Catholic Myths - Slavery, Crusades, Inquisition, Galileo, Holocaust. The myths analyzed in this book claim to lay bare the "dirty history" of the Catholic Church. Well, the Catholic Church's "dirty history" is not that dirty at all. As Pope Leo XIII once said, the Catholic Church has no reason to fear historical truth. Yet, some Catholics as well as many non-Catholics often see history through a lens that has been shaped by post-Reformation propaganda or by 18th century Enlightenment prejudices. These myths served a purpose then, but they still serve a purpose in today's secularist climate of progress and scientism. But does that really validate them? Scholarship of recent decades, however, has thrown new light on these matters, and is finally allowing the truths of history to become more widely known.
• Life's Journey - From Conception to Growing Up, Growing Old, and Natural Death. This book describes the six main phases of life's journey in more or less detail. Some of these stages the reader may have gone through already; others are still ahead of them. They may not be able to retrace previous stages, but they are probably anxious to know what is ahead of them. And besides, they may have children who are going through earlier stages and parents who are experiencing later stages. Each chapter discusses one specific stage of life's journey. Every chapter begins with a biological description of that period in life, followed by a more philosophical reflection. One cannot be without the other. We need facts before we can reflect, but facts without reflection are meaningless.
• Matters of Life and Death - A Catholic Guide to the Moral Dilemmas of Our Time. We live in a time of very divergent opinions about right and wrong, life and death, sexuality and sex, pro-life and pro-choice, prolonging life and shortening life. We all wonder what can help us to pilot through the raging waters of this turbulent ocean. Where do we find sound judgments in the midst of these debates? What we need more than ever is a moral compass.
• Aquinas and Modern Science - A New Synthesis of Faith and Reason. What could Aquinas ever contribute to our time, some seven centuries later? One of the main reasons is that there are many similarities between his time and our time, between his world and our world. His thirteenth century world was as turbulent as ours is. His world was confronted with an influx of new ideas coming from the Muslim world; our world is constantly being inundated with new ideas, particularly coming from scientists. His world saw the sudden rise of universities; our world sees an explosion of sciences and their sub-disciplines. His time was marked by dubious philosophies; our time has been infiltrated with skepticism and relativism. His era was a time of tremendous change; ours is also in permanent instability. His world had lost faith in reason; ours has too. Aquinas understood both the fascination of his contemporaries with new discoveries and new ideas and the very mixed feelings that come with all of that. So he would understand our time too.
• The Holism-Reductionism Debate - In Physics, Genetics, Biology, Neuroscience, Ecology, Sociology. This book is intended for those working in, or preparing for, research in any scientific field — ranging from the physical sciences to the life sciences to the behavioral sciences and the social sciences. It is certainly not meant for people specialized in areas dealing with the specific issue of reductionism in a strict philosophical sense; they won't learn much new from this book. Philosophers have the task of questioning and analyzing what most other people, including scientists, usually take for granted. For that reason, this book is basically a plea against dogmatism in science, in favor of a more open-minded approach. Dogmas do not belong in science, but they do occur in the scientific community.
• The Myth of an Anti-Science Church - Galileo, Darwin, Teilhard, Hawking, Dawkins. What do these five scientists have in common? General perception has it that something went wrong between them and the Catholic Church. Is that true, or are we dealing with a fabrication? If it is true, what exactly went wrong between them? This book analyzes these five "cases" in their confrontation with the Catholic Church. Usually the Church ends up being the villain. But what about these scientists themselves? One could make the case that all five of them have something like a double personality: the personality of the scientist and the personality of the ideologist hiding behind the scientist.
• At the Dawn of Humanity - The First Humans. This book investigates in the first five chapters how genes may change from generation to generation — before, during, and after the dawn of humanity. Next the book discusses how much these mechanisms can explain of what many people consider unique to humanity: the faculties of language, rationality, morality, self-awareness, and religion. Are those features really unique, or did they come from the non-human animal world? Were the first humans able to use language, to think rationally, to act morally, to know who they were, and to know there is a God? The answer may surprise you.
• Faith and Reason - The Cradle of Truth. The reciprocal relationship between faith and reason has been a constant theme in Catholic intellectual history, and it explains why the Catholic intellectual tradition is so rich, strong and full, perhaps unlike anything else in the world. In his famous Regensburg address and elsewhere, Pope Benedict XVI stressed the perennial relevance of Pope John Paul II's encyclical Fides et Ratio (Faith and Reason) and the need for Faith to purify Reason, and for Reason to purify Faith.
• Forty Anti-Catholic Lies. Catholics are believed to have certain beliefs "out of line" with mainstream thinking. However, those beliefs are often caricatures that are misrepresentations of the real beliefs Catholics hold. What do Catholics really believe? Asking any Catholic is not always the best way to find out, for some Catholics may not even know the finer details of their own faith, or they have already been affected by the misinformation that keeps bombarding them.
• The Eclipse of God. This book was specifically written for all those who feel lost in a world dominated by ideologies that obscure God. It is hard to pinpoint one particular cause of how we feel in such Godforsaken times and places, but science is likely one of the main perpetrators.

Books and articles

• Verschuuren, Geert (1971). Race and Races. In Heythrop Journal, 12, 164–174
• Verschuuren, Geert M.N. (1981). Modelgebruik in the Wetenschappen. Kok, Kampen, Netherlands ISBN 90-242-2161-7
• Verschuuren, G.M.N., Hans De Bruin, Manfred Halsema (1985, 2001). Grondslagen van de Biologie (3 volumes). Wolters Kluwer, Netherlands ISBN 90-207-1372-8
• Marcum, James and G.M.N. Verschuuren (1986). Hemostatic Regulation and Whitehead's Philosophy of Organism. In Acta Biotheoretica, 35, 123–133
• Verschuuren, Gerard M. (1986), Investigating the Life Sciences: An Introduction to the Philosophy of Science. In the series Foundations & Philosophy of Science & Technology, Pergamon Press ISBN 0-08-032031-7
• Verschuuren, Gerard M. (1995), Life Scientists: Their Convictions, Their Activities, and Their Values. Genesis Publishing Company, North Andover, MA ISBN 1-886670-00-5
• Verschuuren, Gerard M. (1905–present), The Visual Learning Series (10 different titles published so far). Holy Macro! Books, Uniontown, OH
• Verschuuren, Gerard M. (2007). From VBA to VSTO. Holy Macro! Books, Uniontown, OH ISBN 1-932802-14-2
• Verschuuren, Gerard M. (2013). Excel 2013 for Scientists and Engineers. Holy Macro! Books, Uniontown, OH ISBN 978-1-932802-35-1
• Verschuuren, Gerard M. (2013). VBScript Programming. Holy Macro! Books, Uniontown, OH ISBN 978-1615470181
• Verschuuren, Gerard M. (2012). Darwin's Philosophical Legacy - The Good and the Not-So-Good. Lexington Books, Lanham, MD ISBN 978-0-7391-7520-0 (hardcover), ISBN 978-0-7391-9058-6
• Verschuuren, Gerard M. (2012). God and evolution? - Science Meets Faith. Pauline Books & Media, Boston, MA^[13] ISBN 978-0-8198-3113-2
• Verschuuren, Gerard M. (2012). What Makes You Tick? - A New Paradigm of Neuroscience. Solas Press, Antioch, CA ISBN 978-1-893426-04-7 (softcover) and ISBN 1-893426-04-1 (eBook)
• Verschuuren, Gerard M. (2012). Of All That Is, Seen and Unseen - Life-Saving Answers to Life-Size Questions. Queenship Publishing, Goleta, CA ISBN 978-1579184148 (softcover) and ISBN 1579184146 (eBook)
• Verschuuren, Gerard M. (2014). The Destiny of the Universe - In Pursuit of the Great Unknown. Paragon House Publishers, Saint Paul, MN ISBN 978-1-55778-908-2 (softcover)
• Verschuuren, Gerard M. (2014). It's All in the Genes! - Really?. Createspace, Charlestown, SC  ISBN 978-1496031686
• Verschuuren, Gerard M. (2015). Five Anti-Catholic Myths - Slavery, Crusades, Inquisition, Galileo, Holocaust. Angelico Press, Kettering, OH  ISBN 978-1-62138-128-0
• Verschuuren, Gerard M. (2015). Life's Journey - From Conception to Growing Up, Growing Old, and Natural Death. Angelico Press, Kettering, OH  ISBN 978-1-62138-164-8
• Verschuuren, Gerard M. (2016). Aquinas and Modern Science - A New Synthesis of Faith and Reason. Angelico Press, Kettering, OH  ISBN 1621382281
• Verschuuren, Gerard M. (2016) Religion Viewed from Different Sciences in: On Human Nature: Biology, Psychology, Ethics, Politics, and Religion by Michel Tibayrenc (Editor), Francisco J. Ayala (Editor), pp. 675–685.
• Verschuuren, Gerard M. (2017). 130 Excel Simulations in Action. Createspace, Charlestown, SC ISBN 978-1978429871
• Verschuuren, Gerard M. (2017). 100 Excel VBA Simulations. Createspace, Charlestown, SC ISBN 978-1540445179
• Verschuuren, Gerard M. (2017). The Holism-Reductionism Debate - In Physics, Genetics, Biology, Neuroscience, Ecology, Sociology. Createspace, Charlestown, SC  ISBN 978-1542888486
• Verschuuren, Gerard M. (2017). Faith and Reason - The Cradle of Truth. EnRoute Books, St. Louis, MO 
• Verschuuren, Gerard M. (2017). Matters of Life and Death - A Catholic Guide to the Moral Dilemmas of Our Time. Angelico Press, Kettering, OH 
• Verschuuren, Gerard M. (2018). Forty Anti-Catholic Lies. Sophia Institute Press, Manchester, NH 
• Verschuuren, Gerard M. (2018). The Eclipse of God. EnRoute Books, St. Louis, MO 
• Verschuuren, Gerard M. (2018). The Myth of an Anti-Science Church - Galileo, Darwin, Teilhard, Hawking, Dawkins. Angelico Press, Kettering, OH 
• Verschuuren, Gerard M. (2018). At the Dawn of Humanity - The First Humans. Angelico Press, Kettering, OH 
• Verschuuren, Gerard M. (2013). Videos on YouTube.