Astrophysics

Astrophysics terms

1. Aberration With regards to physics, a discontinuity or distortion in an image produced by a lens.
2. Absorption Spectra The spectra of electromagnetic radiation transmitted through a substance, with dark lines indicating the absorption of specific wavelengths.
3. Accelerating Universe One where distance increase faster with time, in contradiction to those where the gravitational attraction of ordinary matter slows down the expansion.
4. Acceleration The right of the lender to demand payment on the outstanding balance of a loan.
5. Angular resolution The smallest angular size that the instrument can resolve.
6. Angular Size The size of an object as viewed from the earth. For example, the moon subtends (covers) an angle of 1/2 of a degree.
7. Anisotropy The difference in the property of a system with changes in direction. In this case, anisotropy refers to the difference in the temperature of the cosmic…
8. Annihilated/annihilation A process in which a particle meets its corresponding antiparticle and both disappear.
9. Anomaly Something that is out of the ordinary. For example if in a set of 1000 two winged, two legged, one headed, (essentially normal) chickens, one of them had…
10. Antimatter Matter made up of elementary particles whose masses are identical to their normal-matter counterparts but whose other properties, such as electric charge…
11. Antiparticle/antiquark/antielectron For most particle types there is another particle type that has exactly the same mass but the opposite value of all other charges.
12. Apparent luminosities The brightness of an object as it appears from the earth. The apparent luminosity does not take into account the distance from the earth to the object…
13. Atoms The smallest unit of matter that possesses chemical properties. All atoms have the same basic structure: a nucleus containing positively charged protons…
14. Background Radiation Filling all space, e.g. the radiation from the early, hot universe.
15. Baryon Subatomic particles comprised of three quarks. Protons (comprised of two up quarks and one down quark) and neutrons (made up of two down quarks and one up…
16. Baryonic Matter Ordinary matter, which is made up largely of baryons.
17. Big Bang The scientific theory of the origin of the universe as an explosion of space and matter, starting from an enormously dense and hot state at some finite…
18. Black Body Spectrum A plot of the intensity of radiation versus wavelength for a black body.
19. c, speed of light The speed that light travels in a vacuum. It is about 3 x 108 m/s (186,000 miles/s).
20. Closed Universe A universe where the geometry of space closes upon itself like the surface of a sphere.
21. cluster Clusters are fixed length blocks of bytes that store data for Microsoft operating systems.
22. Constant of Proportionality When scientists or theoreticians find a mathematical relationship between two quantities, they design an equation, so that, for example, if one quantity…
23. COSMIC Having to do with the universe as a whole.
24. Cosmic Microwave Backgroun (CMB) (CMB) Radiation filling the universe, remaining from the early, hot phase. (It is sometimes called the "primal glow.") Today this radiation has cooled to 2.
25. Cosmological Constant, Λ The energy density of the smooth vacuum. Eisntein introduced it as a component of the universe but later withdrew it.
26. Cosmological Principle A principle invoked in cosmology that severely restricts the large variety of possible cosmological theories: On large scales, the Universe is homogeneous…
27. Cosmology The study of the universe as a whole, of the contents, structure, and evolution of the universe from the beginning of time to the future.
28. Coupled to Radiation Matter, such as charged particles, that is strongly affected by radiation.
29. Critical Density The density of matter/energy that would just halt the expansion of the universe. The dividing line between a collapsing and an ever-expandinguniverse.
30. Curvature of Spacetime According to Einstein's General Theory of Relativity, mass curves space and time.
31. Dark Energy An energy causing the acceleration of the expansion of the universe, detectable through its gravitational effects.
32. Dark Matter Matter not visible to us because it emits no radiation that we can observe, but it is detectable gravitationally. A small fraction of it is baryonic, e.g.
33. Deceleration Decreasing the velocity (of expansion).
34. Density Fluctuations in Matter Regions of greater and lesser mass density, which can form into structure such as galaxies, clusters, etc.
35. Deuterium A special form of hydrogen (an isotope called "heavy hydrogen") that has a neutron as well as a proton in its nucleus.
36. Doppler Effect apparent change in frequency of a wave due to the relative motion of the source and observer.
37. Dynamics Changes over a length of time.
38. Electromagnetic Force The fundamental force which binds electrons to atoms, and governs the physics of light. Any charge feels an electric force from another charge.
39. Electromagnetic Radiation (ee-LEK-troh-mag-NEH-tik ray-dee-AY-shun) Low-energy radiation that comes from the interaction of electric and magnetic fields.
40. Electron A sub-atomic particle that has a negative electric charge.
41. Elementary Particle Physics The study of fundamental particles (such as quarks and leptons) and their interactions (forces).
42. Energy Density The amount of energy per unit volume. The energy density affects, and is affected by, the expansion or contraction of the universe.
43. Energy Spectrum The amount of energy emitted at a specific wavelength of light. For example, the Sun emits light at many wavelengths, which can be seen by passing…
44. Equilibrium To be in a state of perfect balance. A spinning top is a kind of equilibrium untill it falls.
45. ERA A time period dominated by a particular physical process.
46. Evolution Changing with time.
47. Extrapolate To create new information based on what is already there.
48. Feed A component that "feeds" the signal from the optical system to the amplification electronics. Also called a "feed horn" or "horn".
49. Finite Having a set amount. A barrel of 30 apples contains only 30 apples. However the number of times one can divide a meter into two parts is infinite.
50. Fission The splitting of heavier atomic nuclei into lighter ones. In the case of heavy atoms (e.g., uranium, plutonium), this will release energy.
51. Flat Universe A universe where the geometry of space does not curve but is flat like a tabletop. In a flat universe the total energy density equals the critical density.
52. Flatness Problem Under normal gravity, any slight deviation from flatness should quickly get larger : for example a closed universe should recollapse or an open universe…
53. Fluctuation The deviations from expectation in a player's bankroll.
54. Flux The amount of energy passing through a unit area (for example, 1m2) per time. On this website, we will be discussing the flux of light energy due to…
55. Frame of Reference The perspective from which an event is viewed. For example a man is standing on the side of the road, and he sees a woman drive past him in a car.
56. Fundamental Interactions In the Standard Model the fundamental interactions are the strong, electromagnetic, weak, and gravitational interactions (forces).
57. Fundamental Particles A particle with no internal substructure. In the Standard Model the quarks, leptons, photons, gluons, W+ and W- bosons, and the Z bosons are fundamental.
58. Fusion The combining of lighter elements into heavier ones. For lighter elements (e.g., hydrogen, helium) this process releases energy.
59. Galaxy A cluster of stars held together by their own gravity, and apparently dark matter as well.
60. General Relativity See Relativity.
61. Geocentric A model of the universe, believed by Aristotle, and Ptolemy which puts the earth at the center.
62. Geometries Models of the curvature of the universe in which the laws of geometry are like those that would apply on flat, spherical, or saddle-shaped surfaces.
63. Globular Clusters A collection of hundreds of thousands of old stars held together by gravity.
64. Gluon The carrier particle of the strong interactions. It holds quarks together and the atom's nucleus together.
65. Gravitational Attraction The interaction of particles due to their mass/energy.
66. H₀, Hubble Constant A measure of the expansion rate and age of the universe. It appears to be between 60 and 80 kilometers per second per megaparsec.
67. Heavenly Bodies Any mass or object in space, including nebulas, planets, moons, stars, pulsars, quasars and so on.
68. Heliocentric A model of the universe published by Nicolaus Copernicus, and proven by Galileo (who viewed the phases of venus with his telescope), which puts our sun at…
69. High Electron Mobility Transistor (HEMT) (HEMT) This is a particular kind of transistor that is especially appropriate for use in microwave amplifiers.
70. Homogeneous Looking the same at every location. Homogeneous milk has no lumps or impurities; it remains the same no matter where you look.
71. Hubble's Law The redshift in light coming from distant galaxies is proportional to their distance from earth.
72. Hypothesis A tentative proposal made to explain certain observations or facts that requires further investigation to be verified.
73. Inflation A condition of increasing prices. Inflation is generally measured by the Consumer Price Index.
74. Inhomogeneity Something not evenly distributed in space; a clump or cluster.
75. Initial Being first, before anything else occurs.
76. Initial Conditions The nature of a system's state when time equals zero.
77. Intensity With regards to light, intensity is the energy moving through a region of area per unit of time.
78. Intrinsic Luminosity A measure of the true brightness of an object. It is the amount of energy radiated into space every second by a celestial object, such as a star.
79. Inverse Square 1 divided by a quantity squared. 1/(r^2). The force due to gravity is proportional to 1 over distance squared. F~1/(d2).
80. Ion An atom or molecule that has lost or gained one or more electrons and has become electrically charged as a result.
81. Ionized The state in which an atom is missing on or more of its electrons, and is therefore positively charged.
82. Isotopes atoms that have the same number of protons, but a different number of neutrons are isotopes of each other.
83. Isotropic the property of being independent of direction. Isotropic radiation has the same intensity regardless of the direction of measurement.
84. Kelvin One Kelvin degree is equivalent to one Celsius degree. The difference between the two temperature scales: All motion within an atom ceases at zero Kelvin…
85. Lambda, Λ The cosmological constant, which measures the energy density of the vacuum.
86. Large Scale Structure Galaxies, galaxy clusters, and galaxy superclusters.
87. Last Scattering Surface The farthest back in the history of the universe that photons could travel freely.
88. Light A pane of glass; a window, or a compartment of a window.
89. Light Year The distance light travels in a year: {Distance equals rate times time: 300,000,000 meters per second, times roughly 30 million seconds equals roughly} 9.
90. Local Group A small cluster of more than 30 galaxies "near" to our galaxy, including the Andromeda galaxy and the Magellanic Clouds.
91. Luminosity The total energy released by an object emitting light, (in our case, this will be a star) per unit time (usually per second).
92. Main Sequence Star A star that lies along a continuous band, known as the main sequence, extending from the upper left (hot, bright stars) to the lower right (cool, dim…
93. Mass Defect When two subatomic particles are bound together, their bound mass is slightly different than their mass if each particle is measured separately.
94. Matter-Dominated Universe When the density of matter is greater than that of any other component.
95. Meson A kind of matter made from an even number of quark-antiquark constituents. The basic structure of most mesons is one quark and one antiquark.
96. Metastable Energy Density A theorized transient energy, often preceding a phase transition.
97. Mid-Class Explorer (MIDEX) (MIDEX) NASA's Mid-Class Explorer.
98. Milky Way The galaxy in which the Earth is found. When viewed from the Earth and its environs, it appears in the night sky as a hazy band of white light (hence…
99. model See Exhibit.
100. Muon The second heaviest charged lepton (with electron and tau), with electric charge -1.