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Topic: Astronomical constant

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gravitational constant

cosmological constant

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	History & info - Astronomical basis of calendars, history
		The principal astronomical cycles are the day (based on the rotation of the Earth on its axis), the year (based on the revolution of the Earth around the Sun), and the month (based on the revolution of the Moon around the Earth).
		The astronomical "tropical year" is frequently defined as the time between, say, two vernal equinoxes, but this is not actually true.
		The astronomer's mean tropical year is really a somewhat artificial average of the period between the time when the sun is in any given position in the sky with respect to the equinoxes and the next time the sun is in the same position.
	webexhibits.org /calendars/year-astronomy.html (2301 words)

	astronomical constant concept from the Astronomy knowledge base (Site not responding. Last check: 2007-10-09)
		The size of the cosmological constant is designated by the Greek letter lambda (λ)., A term sometimes employed in cosmology to express a force of "cosmic repulsion", such as the energy released by the false vacuum thought to power exponential expansion of the universe in the inflationary universe models.
		Current indications are that this constant must be zero, but the reason for its vanishing remains a mystery., A term introduced by Einstein into his field equations of gravitation to permit a static model of the universe.
		For a flat universe with no cosmological constant, the age of the universe is two-thirds of the Hubble time., The inverse of the Hubble constant and a crude measure of the universe's age.
	www.site.uottawa.ca:4321 /astronomy/astronomicalconstant.html (1208 words)

	Constant - Wikipedia, the free encyclopedia
		Constants are by convention usually denoted by lower-case letters from the beginning of the English alphabet, such as a, b, and c.
		In a polynomial (or a generalisation of a polynomial, such as a Taylor series or Fourier expansion), the constant term is associated to the exponent zero.
		Thus, there is no precise definition of "constant" in mathematics; only phrases such as "constant function" or "constant term of a polynomial" can be defined.
	en.wikipedia.org /wiki/Constant (609 words)

	Astronomical unit Summary
		Astronomers were able to use the resources of their schools and observatories to work together to produce accurate and complete catalogs of the stars.
		While the value of the astronomical unit is now known to great precision, the value of the mass of the Sun is not, because of uncertainty in the value of the gravitational constant.
		Because the gravitational constant is known to only five or six significant digits while the positions of the planets are known to 11 or 12 digits, calculations in celestial mechanics are typically performed in solar masses and astronomical units rather than in kilograms and kilometres.
	www.bookrags.com /Astronomical_unit (2532 words)

	Astronomical problems
		This constant is used to calculate the expansion rate of the universe.
		Thus, astronomers are presented with the paradox that the objects in the universe may be much older than the universe itself.
		Closer to home, astronomers are finally concluding after 25 years of measurements that the missing solar neutrinos are really missing.
	www.answersingenesis.org /tj/v9/i1/astronomy.asp (992 words)

	Astronomy in Ancient India - Crystalinks
		This is an extremely accurate ratio of a fundamental astronomical ratio (1,582,237,500/57,753,336 = 27.3964693572), and is perhaps the oldest astronomical constant calculated to such accuracy.Brahmagupta (598-668) was the head of the astronomical observatory at Ujjain and during his tenure there wrote a text on astronomy, the Brahmasphutasiddhanta in 628.
		Another Indian astronomer and mathematician, Brahmagupta estimated in the 7th century that the circumference of the earth was 5000 yojanas.
		About a hundred years before Brahmagupta, another astronomer, Varahamihira had claimed for the first time perhaps that there should be a force which might be keeping bodies stuck to the Earth, and also keeping heavenly bodies in their determined places.
	www.crystalinks.com /indiastronomy.html (2904 words)

	Universe Today » Archive » Chandra Confirms the Hubble Constant (Site not responding. Last check: 2007-10-09)
		The Hubble constant is calculated by measuring the speed at which objects are moving away from us and dividing by their distance.
		Most of the previous attempts to determine the Hubble constant have involved using a multi-step, or distance ladder, approach in which the distance to nearby galaxies is used as the basis for determining greater distances.
		The astronomers used a phenomenon known as the Sunyaev-Zeldovich effect, where photons in the cosmic microwave background (CMB) interact with electrons in the hot gas that pervades the enormous galaxy clusters.
	www.universetoday.com /2006/08/08/chandra-confirms-the-hubble-constant (803 words)

	solar constant - HighBeam Encyclopedia (Site not responding. Last check: 2007-10-09)
		solar constant the average amount of radiant energy received by the earth's atmosphere from the sun; its value is about 2 calories per min incident on each square centimeter of the upper atmosphere.
		The actual value of the energy varies with several factors; the most important factor is the earth's distance from the sun, which changes because of the earth's elliptical orbit.
		For computing the value of the solar constant, the astronomical unit, or average earth-sun distance, is used.
	www.encyclopedia.com /doc/1E1-solarcon.html (279 words)

	WMAP Cosmology 101: Expansion of the Universe
		Astronomers observed Cepheids in both the metal rich inner region of the Andromeda galaxy and its metal poor outer region.
		Astronomers also found that Type Ia supernova, which are thought to be due to the explosive burning of a white dwarf star, all had nearly the same peak luminosity.
		The key project determination of the Hubble constant is consistent with a number of independent efforts to estimate the Hubble constant: a recent statistical synthesis by G.F.R. Ellis and his collaborators of the published literature yields a value between 66 and 82 (km/sec)/Mpc.
	map.gsfc.nasa.gov /m_uni/uni_101expand.html (1581 words)

	Astronomical Redshift
		Studying astronomical redshift via spectral and photometric techniques has been an intensive astrophysical activity since 1929 when Hubble announced that galaxies are moving away from each other, i.e.
		Astronomical redshift is the lengthening of emitted radiation as detected by observers.
		Cosmological redshift is caused by the relativistic expansion of the universe, as quantified by the Hubble constant, H
	www.asterism.org /tutorials/tut29-1.htm (906 words)

	New quasar studies keep fundamental physical constant constant
		Previous astronomical measurements of the fine structure constant - the dimensionless number that determines the strength of interactions between charged particles and electromagnetic fields - suggested that this particular constant is increasing very slightly with time.
		Well-known examples are the gravitational constant, which defines the strength of the force acting between two bodies, such as the Earth and the Moon, and the speed of light.
		If the fine-structure constant happens to change over the duration of the light's journey, the energy levels in the atoms would be affected and the wavelengths of the absorption lines would be shifted by different amounts.
	www.eurekalert.org /pub_releases/2004-03/eso-nqs033104.php (1625 words)

	Imagine the Universe! Dictionary
		Astronomically, it is half the angle which a a star appears to move as the earth moves from one side of the sun to the other.
		The fundamental constant equal to the ratio of the energy of a quantum of energy to its frequency.
		The supplementary SI unit of angular measure, defined as the central angle of a circle whose subtended arc is equal to the radius of the circle.
	imagine.gsfc.nasa.gov /docs/dictionary.html (10553 words)

	Dictionary of Technical Terms for Aerospace Use - G
		The universal gas constant is R = 8.3143 joules/degrees K-mol The gas constant for a particular gas, specific gas constant, r = R/ m where m is the molecular weight of the gas.
		Azimuth or orientation of the line, given the longitude, is determined by astronomic observations.
		In celestial mechanics, G may be used as a symbol with units unspecified or in a particular problem may be made equal to 1 or 4 pi squared by the choice of units for other parameters in the particular problem.
	roland.grc.nasa.gov /~dglover/dictionary/g.html (5751 words)

	Astronomers Crunch Numbers, Universe Gets Bigger (Site not responding. Last check: 2007-10-09)
		This finding implies that the Hubble constant, a number that astronomers rely on to calculate a host of factors -- including the size and age of the universe -- could be significantly off the mark as well.
		The astronomers came to this conclusion after they invented a new method for calculating intergalactic distances, one that is more precise and much simpler than standard methods.
		Astronomical Institute of the University of Erlangen-Nuremberg in Germany.
	researchnews.osu.edu /archive/biguni.htm (850 words)

	The Harvard Crimson :: News :: Research Points to Younger Universe, New Value for Astronomical Constant
		Hubble's Constant, named after the late astronomer Edwin P. Hubble, sets the ratio of the velocity of objects to their distance.
		Huchra and his colleagues conclude that astronomers came up with an incorrect value for Hubble's Constant because they limited their observations to relatively nearby clusters of galaxies--those less than 70 million light years away.
		Astronomers at Harvard and elsewhere reacted to Huchra's research with approval and cautious acceptance.
	www.thecrimson.com /article.aspx?ref=109674 (452 words)

	Galaxies
		Astronomers have then been able to discover that most of the mass in our Galaxy is not producing light of any kind and is in a dark halo around the visible parts of the Galaxy.
		Radar reflections from Venus and its angular separation from the Sun are used to calculate the numerical value of the Astronomical Unit (AU).
		With the Hubble Space Telescope, astronomers were able to use the Cepheid period-luminosity relation out to distances ten times further than what could be done on the ground.
	www.astronomynotes.com /galaxy/s16.htm (1776 words)

	The Cosmic Distance Ladder, III: Measuring the Hubble Constant
		So important is measurement of the Hubble constant that many of the century's greatest astronomers have spent their entire careers working on the topic, and a principal justification for the Hubble Space Telescope was to measure it.
		Hence, if the constant of proportionality is known, the distance can be determined to any galaxy, provided is speed of recession.
		The formula for using the Hubble Constant to calculate age of the universe is supposed to be
	www.suite101.com /article.cfm/astronomy/13754 (568 words)

	Terrestrial and astronomical refractions
		Remember Laplace's theorem: near the horizon, the astronomical refraction is proportional to the air mass in the line of sight.
		A constant lapse rate corresponds to a constant terrestrial refraction coefficient, which is the ratio k of curvatures of the ray and the Earth.
		But, until then, astronomers are content to stay away from the horizon, and work in the region where Oriani's theorem promises a refraction that depends only on the local temperature and pressure.
	mintaka.sdsu.edu /GF/explain/atmos_refr/terrestrial.html (1916 words)

	constants
		Constants that aren't dimensionless can be regarded as relating one sort of unit to another.
		The electromagnetic coupling constant is just another name for the fine structure constant; it describes the strength of the electromagnetic field.
		Instead of the electromagnetic coupling constant together with the masses of the W, Z, and Higgs, we could have used 4 other constants: the U(1) coupling constant, the SU(2) coupling constant, the mass of the Higgs, and the expectation value of the Higgs field.
	math.ucr.edu /home/baez/constants.html (1705 words)

	Glossary of Astronomical and Cosmological Terms
		cosmological constant: a term in Einstein's general relativity equations that leads to an acceleration of the expansion of the Universe.
		parsec: a unit of distance used by astronomers, corresponding to a parallax of one arc-second.
		The eye is sensitive to waves from violet at 380 nm wavelength to red at 700 nm wavelength, but astronomers now study electromagnetic radiation from gamma rays through X-rays, ultraviolet, violet, blue, green, yellow, orange, red, infrared and radio waves.
	www.astro.ucla.edu /~wright/glossary.html (1935 words)

	astro (Site not responding. Last check: 2007-10-09)
		Furthermore, as Arizona astronomer William Tifft and others have shown, the redshift of light from distant galaxies is quantised, or goes in "jumps".
		The second area where astronomers have felt that mass is "missing" is due to the behaviour of rotation rates of galaxies as you go out from their centres.
		For the last two decades, astronomer William Tifft of Arizona has pointed out repeatedly that the redshift is not a smooth function at all but is, in fact, going in "jumps", or is quantised.
	www.setterfield.org /AstronomicalDiscussion.htm (11260 words)

	Zoom Astronomy Glossary: G
		G is Newton's gravitational constant (also called the universal gravitational constant), a fundamental constant of nature that determines the strength of the force of the gravitational interaction between objects.
		Johann Gottfried Galle (1812-1910) was a German astronomer who discovered the crepe ring of Saturn (in 1838) and was a co-discoverer (with d'Arrest) of Neptune (in 1846).
		The gravitational constant (abbreviated G) is the constant of proportionality in Newton's equation (formulated in 1666) that describes the gravitational attraction between objects; their gravitational attraction (F) depends only on their masses and the distance between them, according to the formula
	www.enchantedlearning.com /subjects/astronomy/glossary/indexg.shtml (3017 words)

	The Àryabhatíya of Àryabhata by J. Q. Jacobs (Site not responding. Last check: 2007-10-09)
		Given Jan. 1, 2000 astronomical constants and given the present day formulas to temporally adjust the astronomical constants, I calculated that Àryabhata's ratio was exact for 1604 BC.* The resulting data is presented in Table 1.
		To avoid excessively large numbers, later astronomers changed the beginning of the epoch to the Kali era, commencing at midnight of 17-18 February of 3102 B.C. The Àryabhatiya is a summary of Hindu mathematics up to his time, including astronomy, spherical trigonometry, arithmetic, algebra and plane trigonometry.
		To date I have found no indication of older accurate astronomical constants or published indications of modern writers noticing the accuracy of the data discovered in the Indian sources.
	www.jqjacobs.net /astro/aryabhata.html (1220 words)

	astronomical unit
		In 1976 the 16th General Assembly of the International Astronomical Union defined the astronomical unit of length (as part of the International System of Astronomical Constants) as “that length for which the Gaussian gravitational constant (k) takes the value 0.
		The astronomical unit of time is the day, defined as 86,400 seconds (the second as defined in SI), and the astronomical unit of mass is the mass of the sun, by definition 1.
		that 1) dimensions of celestial bodies, velocities, etc. be described in kilometers, 2) "la distance moyenne du soleil à la terre, ou unité astronomique" [the average distance between the sun and earth, or astronomical unit] be used for distances in the solar system and 3) the parsec be used for distances to stars.
	www.sizes.com /units/astronomical_unit.htm (346 words)

	published in SCIENCE
		Relaxation oscillators tend to lose their phase stability (and their narrow spectral peaks) unless the energy exchange mechanisms are exceptionally constant over many cycles, a condition not expected to be met in the geophysics of climate.
		This is a general argument for the astronomical origin of the 41 k.y.
		The orbits of the dust particles depend strongly on size, since their path to the Earth is determined primarily by the Poynting-Robertson effect (viscosity from sunlight), and while enroute to the Earth their orbits are perturbed by Jupiter and the other planets.
	muller.lbl.gov /papers/sciencespectra.htm (3559 words)

	Calvin and the Astronomical Revolution
		And the arguments over the shape of the universe were not constrained to the classrooms and lecture halls of science, for the new theory presented such a radical reinterpretation of the physical world that it impacted many fields of human inquiry.
		This device supposes that the heavenly body moves with constant, circular motion; however, the center of its path is not the center of the earth, but is removed to some distance from it.
		Osiander believed that the work of astronomers was simply to "save the phenomena"; that is, astronomers were properly concerned only with being able to predict the motion of the heavenly bodies, without necessarily making any claim on the physical construction of the universe.
	www.nd.edu /~mdowd1/postings/CalvinAstroRev.html (5552 words)

	Basic Astronomical Terms
		Here some basic astronomical terms, relevant for the SEDS Messier database, are shortly explained, in the hope to help beginners.
		The distance from which the mean distance of Earth's orbit around the Sun, the astronomical unit (AU), appears under the angle of 1 arc second.
		The celestial coordinate corresponding to latitude is the Declination.
	www.seds.org /messier/xtra/Terms/terms.html (939 words)

	ASSA African Astronomical History Symposium 2005
		The occasion was an opportunity to talk about the increased interest in the traditional beliefs of the indigenous peoples of southern Africa as well as an opportunity to reflect on the contribution of the (mainly foreign-founded) observatories to main-line scientific astronomy.
		The first day was devoted primarily to indigenous African astronomical ideas and beliefs, while the second dealt with contributions to modern astronomy.
		The AFP is a comprehensive plan for the structure and funding of astronomy in the future and the discussion was intended to cover what might be called the humanistic aspects of the programme – for example studies of the place and meaning of the night skies in African society past and present.
	www.saao.ac.za /assa/aahs (2655 words)

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