Astronomy, Physics, Science, Technology Glossary

This is primarily an astronomy glossary, but other related and/or useful terms creep in as well.

I've attempted to keep the definitions and explanations brief with few or no references.

In many cases I've just left links to definitions longer definitions, discussions, references, examples, images, lists, etc. Some links do not exist yet. The links may be to pages of other persons.

A	B	C	D	E	F	G	H	I
J	K	L	M	N	O	P	Q	R
S	T	U	V	W	X	Y	Z

acronyms: (a) A word formed from the initial letters of other words. (b) Multi-word designations abbreviated by the first letters of the words.
Aristarchos of Samos (3rd century BC): Greek mathematician and astronomy: the first known proposer of the heliocentric model of the solar system.
Aristotle of Stagira (384--322 BC): Greek philosopher.
asteroid: A rocky body in space larger than of order 10 meters, but not classified as a moon or as planet (i.e., it is too small to be a planet).
astronomer: A scientist engaged in the study things in space.
astronomical unit (AU): The mean Earth-Sun distance treated as a unit: 1 AU = 1.4959787*10**13 cm = 1.496*10**13 cm = 1.5*10**13 cm.
Avebury: A Neolithic stone circle in Wiltshire, England, not far from Stonehenge.

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Bertrand, Joseph Louis Francois (1822-1900): A 19th century mathematician perhaps best remembered for Bertrand's theorem which concerns the types of central forces lead to closed orbits.
Big Bang: (a) The singularity of infinite density that occurs at the universal time zero of Friedmann-Lemaitre-Lambda models of the universe or similar models. The name was originally derisory and was first used by Fred Hoyle in a BBC radio program: Hoyle was a coinventor of the steady-state model of the universe. The singularity was sometimes called the point origin in earlier work Bo-85,181. (b) The short time after the singularity in which the light elements are sysnthesized.
Big Bang Cosmology: The theory that the universe or our universe domain began from a hot dense state in which the light elements were synthesized and then that the universe evolved according to Friedmann-Lemaitre-Lambda model of the universe or similar model. Such models formally have a time zero singularity of infinite density (i.e., the (return to top)

C
1. Carnot, Sadi (1796--1832): A French scientist noted for his theoretical discovery of the Carnot engine: the most efficient heat engine that the laws of thermodynamics allows.
2. Celestial Sphere: A large imaginary sphere center on the Earth. On this sphere the astro-bodies can be located uniquely for a terrestrial observer if all parallax effects can be neglected.
3. center of mass: The mass-weighted average position of a body.
4. Chaucer, Geoffrey (1343?--1400): English poet, most famous for The Canterbury Tales. By the standards of his day he was exceptionally knowledgeable about astronomy and often included astronomical details in his works.
5. comet: (a) An icy/rocky body typically a few kilometers or tens of kilometers in size scale in a highly elliptical orbit about the Sun. When close to the Sun the ices explosively evaporated and create the large cometary head and tail. (b) The comet head and tail.
6. compact object: Super-dense astro-bodies: white dwarfs (WDs), neutron stars (NSs), and black holes (BHs).
7. constellation: (a) A recognized grouping in angle of stars on the sky. (b) Any of the 88 IAU recognized constellations and their defined surrounding angular areas on the sky.
8. Copernican principle: This principle is really an assumption: it states that we occupy no special place in the universe (Bo-13; CL-4). It is one of the simplifying guiding principles of cosmology: i.e., it guides us in constructing cosmological model. There is no observational evidence or broadly accepted theoretical reason to suggest the Copernican principle is false. In fact, as far as we can tell it seems true.
9. Copernicus, Nicolaus (1473--1543): Polish-German astronomer who was the first modern proposer of the heliocentric model of the solar system.
10. copyright: The ownership of some intangible, conceptual property: e.g, book, image, design.
11. cosmology: (a) The science of the universe as a whole. Also modern cosmology. (b) The philosophy or myth of the universe as a whole.
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D
1. Descartes, Rene (1596--1650): French philosopher often associated with his famous principle. cogito ergo sum: I think therefore I am. He was also astronomical speculator.
2. disaster: An unfortunate event. From Italian for not having a lucky star: derived from disastro and disastrato.
3. Doppler, Johann Christian (1803--1853) Doppler was an Austrian physicist famous for his discovery of the frequency shifting property of relative motion on wave phenomena.
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E
1. Earth: The 3rd planet from the Sun: home of humankind.
2. Einstein, Albert (1879--1955): German-Swiss-American physicist most famous for his discoveries of special relativity (SR) and general relativity (GR).
3. Einstein universe: This is general relativistic model of the universe proposed by Einstein in 1917: it is homogenous and isotropic, hyperspherical (i.e., a finite but bounded 3-dimensional surface of a 4-dimensional sphere), and static (No-520; Bo-97). The model is suppose to represent the average behavior of an actual static universe. To make his universe static, Einstein invented the cosmological constant since pure general relativity failed to give a static universe. He renounced the cosmological constant after the expansion of the universe was discovered: he called it the biggest blunder of his life since introducing it precluded predicting the expansion of the universe himself.
4. ellipse:
5. ephemeris:
6. expansion of the universe: The ongoing increase in distance between the largest gravitionally bound systems in the observable universe. The observed expansion is consistent with the general relativistic Friedmann-Lemaitre-Lambda models.
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F
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G
1. galaxy:
2. Galileo Galilei (1564--1642)
3. Gamow, George (1904--1968): Probably the person best credited as the main originator of the Big Bang theory.
4. gravity:
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H
1. Harriot, Thomas (1560--1621):
2. Hertz, Heinrich (1857--1894): The inventor of radio.
3. Hubble, Edwin Powell (1889--1953):
4. Hubble diagram: A plot of velocity or spectral shift of galaxies or other extragalactic objects versus distance. The systematic relationship is a straight line through the origin. The line is representation of the Hubble law v=Hd.
5. Hubble's law: This is the linear relationship between recessional velocity and distance for extragalactic objects participating in the expansion of the universe. The law is v=Hd, where v is recessional velocity, d is distance, and H is the Hubble constant: H=71 (+4/-3) (km/s)/Mpc is a good modern value (FK-653.
6. Huygens, Christian (1629--1695):
7. hydrodynamics: The science of fluid motion.
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I
1. inflation: The concept that the universe or universe domains undergo sudden enormous expansions from microscopic regions. The expansions flatten the domain.
2. interstellar medium (ISM): The gas and dust between the stars inside of galaxies.
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J
1. Jupiter The 5th planet from the Sun. The largest planet.
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K
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L
1. large-scale structure: The pattern of galaxies and larger galaxy structures: clusters, superclusters, filaments, sheets, and voids.
2. logarithms:
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M
1. magnitudes:
2. Mars: The 4th planet from the Sun.
3. Maxwell, James Clark (1831-1879):
4. Mercury: The 1st planet from the Sun.
5. meteorite:
6. metric prefixes:
7. metric system or SI:
8. Milky Way: Also the Galaxy. (a) The galaxy of humankind and the Sun. (b) The band of whitish luminosity on the sky that straddles a great circle at about 60 degrees from the Celestial Equator. This band is the appearance of the disk of Milky Way from inside the disk.
9. Moon: The Earth's only natural satellite.
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N
1. naked eye star:
2. nebula, pl. nebulae:
3. Neptune: The 8th planet from the Sun.
4. Newton: Sir Isaac Newton (1643--1727):
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O
1. Omar Khayyam:
2. Orion Nebula:
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P
1. planet: A larger body orbiting the Sun or any star.
2. Pluto: The 9th planet from the Sun.
3. polarization:
4. Popper, Sir Karl Raimund: A philosopher of science.
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Q
1. quantum mechanics: The physics of microscopic systems: i.e., atomics scale and smaller.
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R
1. radiative transfer: The transfer of energy and information by electromagnetic radiation.
2. rainbow:
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S
1. Saturn: The 6th planet from the Sun. It is a gas giant planet and has by far the most prominent ring system in the solar system.
2. Schroedinger, Erwin (1887--1961): The co-discoverer of quantum mechanics. He formulate the Schroedinger equation which is the basic law of motion of non-relativistic quantum mechanics.
3. science fiction: Fiction that makes explicit use of scientific conceptions or that it is set in the future or fictional worlds.
4. sky map: A map of the sky locating stars, etc.
5. Slipher, Vesto Melvin (1875--1969): The discovery of the tendency of the spiral nebulae to be redshifted. He worked at Lowell Observatory in Flagstaff, Arizona (No-522--523).
6. solar system: The Sun and the astro-bodies that are gravitationally bound to the sun.
7. star: (a) A large sphere of gas in space that is generating energy by nuclear fusion. (b) A compact object that used to be a star by the first definition and still has star in its name: white dwarfs (WDs) and neutron stars (NSs).
8. star cluster: A gravitationally bound group of stars that is smaller than a galaxy and is itself bound to a galaxy.
9. star evolution: The temporal development of stars.
10. Stonehenge: A neolithic site from 3000--1000 BCE ???? consisting of stone rings and other artifacts. The design includes astronomical information: alignment astronomy.
11. Sun: A G2 V star to which the Earth is gravitationally bound.
12. supernova (SN): The giant explosion of a star.
13. synodic period: The time it takes for an astro-body to return to the same angular position relative to the Sun.
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T
1. Tacoma Narrows Bridge: The bridge that collapsed due to wind-driven resonances.
2. telescope: An optical device whose essential components are lenses and/or mirrors. It is used for seeing objects at optical infinity and is particularly used in astronomy.
3. Tycho Brahe (1546--1601): A Danish astronomer famous for his detailed and copious pre-telescopic observations.
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U
1. unit: A standard amount of any quantifiable thing.
2. universe: Also cosmos. (a) Everything. (b) The part of everything that is similar to the observable universe. (c) The observable universe.
3. universe domain: Also universe patch or pocket universe???. A region of the universe that has the same laws of physics and the same large-scale structure.
  Our domain which is larger than the observable universe (we think) may itself constitute the whole universe, but many people think it does not and that other domains, maybe infinitely many, exist.
4. Uranus: The 7th planet from the Sun. It has blue color due to methane in its atmosphere.
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V
1. Venus The 2nd planet from the Sun. It is the historical Evening and Morning Star.
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W

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X

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Y

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Z
1. Zodiac: A band of about 16 degrees straddling the Celestial Sphere containing the 12 constellations of the Zodiac and the 12 signs of Zodiac which in precise astrology are 30 degree segments along the band.
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