LAWS

• rayleigh-jeans law » in classical physics, an equation that describes the intensity of blackbody radiation as a function of frequency for a fixed temperature
  • led to the ultraviolet catastrophe
• wien's law » tells us that objects of different temperature emit spectra that peak at different wavelengths

EQUATIONS

• distance modulus » m - M
  • the difference between the apparent magnitude (m) and absolute magnitude (M) of a celestial object. provides a measure of the distance to the object, r (in parsec)
• energy of a photon » E = hc / λ
  • where h is planck's constant, c is the speed of light, and λ is wavelength
• resolving power » RP = 25,000"(λ / d)
  • where λ is the wavelength of light, d is the diameter of the objective, and resolving power is expressed as an angle

CONSTANTS

• gravitational constant » 6.67408 × 10 ^ -11 m3 kg-1 s-2
• planck's constant » 6.63 x 10 ^ -34 js
• speed of light » 3 x 10 ^ 8 m/s

TERMS

Aa

• absolute zero » the lowest temperature theoretically possible; 0 degrees kelvin
• accretion disk » a disk of gas that accumulates around a center of gravitational attraction, such as a white dwarf, neutron star, or black hole
• albedo » the reflective property of a non-luminous object
  • a perfect mirror would have an albedo of 100% while a black hole would have an albedo of 0%
• antimatter » matter consisting of particles with charges opposite that of ordinary matter
  • in antimatter, protons have a negative charge while electrons have a positive charge
• aphelion » the point in the orbit of a planet or other celestial body where it is farthest from the sun
• azimuth » the direction of a celestial object from the observer, expressed as an angular distance

Bb

• binary » a system of two stars that revolve around a common center of gravity
• blackbody » a theoretical ideal radiator and absorber of energy at all electromagnetic wavelength s
  • the term comes from the fact that a cold blackbody appears visually black
• black hole » the collapsed core of a massive star
  • stars that are very massive will collapse under their own gravity when their fuel is exhausted
  • the collapse continues until all matter is crushed out of existence into what is known as a singularity
• bolide » a term used to describe an exceptionally bright meteor
  • bolides will typically produce a sonic boom

Cc

• celestial sphere » an imaginary sphere around the earth on which the stars and planets appear to be positioned
• circumpolar star » a star that never sets but rather circles the pole star, polaris
• coma » an area of dust or gas surrounding the nucleus of a comet
• conjunction » an event that occurs when two or more celestial objects appear close together in the sky

Dd

• dark matter » a term used to describe matter in the universe that cannot be seen, but can be detected by its gravitational effects on other bodies
• doppler effect » the apparent change in wavelength of sound or light emitted by an object in relation to an observer's position
  • an object approaching the observer will have a shorter wavelength (blue) while an object moving away will have a longer (red) wavelength

Ee

• eccentricity » the measure of how an object's orbit differs from a perfect circle
  • a value of 0 is a circular orbit
  • values between 0 and 1 form an elliptical orbit
  • 1 is a parabolic escape orbit
  • greater than 1 is a hyperbola
• eclipsing binary » a binary system where one object passes in front of the other, cutting off some or all of its light
• ecliptic » an imaginary line in the sky traced by the sun as it moves in its yearly path through the sky
• einstein ring » an apparent ring of light caused by gravitational lensing of a distant object when its light passes by a nearer massive object
  • to get the einstein ring requires perfect geometric alignment
• ejecta » material from beneath the surface of a body such as a moon or planet that is ejected by an impact such as a meteor and distributed around the surface
  • ejecta usually appear as a lighter color than the surrounding surface
• elliptical galaxy » a galaxy whose structure is shaped like an ellipse. it is smooth and lacks complex structures such as spiral arms
  • more three-dimensional than a spiral galaxy, without much structure, and their stars are in somewhat random orbits around the center
• event horizon » the theoretical boundary around a black hole beyond which no light or other radiation can escape

Gg

• galaxy cannabalism » smaller galaxies consumed by collision or by being drawn into a larger galaxy
  • this process may cause changes in the shape and form of the larger galaxy and change its evolutionary pattern
• gallilean moons » the name given to jupiter's four largest moons: io, europa, callisto & ganymede

Hh

• head-tail galaxy » a radio galaxy moving through intergalactic space that has its outer portions (where the radio emission comes from) swept backward into the shape of a tail

Rr

• radio galaxy » a galaxy that emits more energy at radio wavelengths than at visible wavelengths

Ss

• solar winds » the continuous flow of charged particles from the sun that permeates the solar system
• starburst galaxy » a class of galaxy characterized by periodic outbursts of star formation over widespread regions in the galaxy

Tt

• tidal encounter » the nearby passage of a galaxy that stretches its companion by exerting unequal gravitational forces on each side
  • may result in the "grand design" structure of spiral galaxies

Uu

• ultraviolet catastrophe » the error at short wavelengths in the rayleigh–jeans law for the energy emitted by an ideal black-body

Vv

• void » vast spaces between filaments (the largest-scale structures in the universe), which contain very few or no galaxies
  • super void » a particularly large void, defined by the absence of rich superclusters