AstronomyThe study of objects and matter outside the earth's atmosphere and of their physical and chemical properties
Light Year• A unit of
distance in astronomy; distance that light travels in one year or about 5.88 trillion miles (9.46 trillion kilometers)
Universe
• The entire celestial cosmos
Star A light-radiating gaseous celestial body of great mass which produces energy by means of nuclear fusion reactions
Galaxy• Any of the
very large groups of stars and matter that are found throughout the universe
System• a group of
related natural objects or forces
Milky Way GalaxyThe galaxy of which the Sun and the solar system are a part and which contains the many stars that make up the galaxy
Big Bang TheoryTheory that states that the universe originated billions of years ago in an explosion from a single point of nearly infinite energy density
Cluster
A collection of stars or galaxies that appear close together in the sky and are gravitationally associated
Telescope• An optical instrument for viewing distant objects.
Eyepiece Lens
• The lens of a telescope that makes the image larger
Objective Lens
• The lens of a telescope that collects and focuses light
Spiral Galaxy
Galaxy that looks like a flat disk with a bulge in its center and spiral arms
Constellation
Groups of stars that seem to form patterns in the sky.
Polaris
The star that is above Earth’s north pole
SpectroscopeAn instrument for forming and examining spectra.
Galaxy
A huge, gravitationally bound system of stars, interstellar gas and dust
SunThe star in our Solar System, which all the planets orbit
Apparent Magnitude
A star’s brightness as it appears from Earth
Absolute Magnitude
A star’s actual size and temperature
Nebula
A cloud of gas and dust in outer space
Astronomical UnitUsed to measure distances within our solar system; the average distance between the Sun and the Earth; about 150 million kilometers; AU
Period of Revolution The motion
of the planet in its orbit around the Sun; the Earth’s revolution is 1 year
Period of RotationThe time it takes for one complete spin of a planet on its axis; the Earth’s rotation is 1 day
Inner PlanetMercury, Venus, Earth, Mars; much smaller and less massive than the outer planets
Outer PlanetJupiter, Saturn, Uranus, Neptune; more gaseous, larger and less dense
CometA small body orbiting the Sun and occasionally exhibits an atmosphere and a tail
AsteroidChunk of rock and metal and found between the orbits of Mars and Jupiter in the asteroid belt.
Meteoroid
A chunk of rock that orbits the Sun
Meteorite
A meteoroid that has entered the Earth’s atmosphere.
Red ShiftA movement of the spectrum of a celestial body toward longer wavelengths that is a result of the Doppler effect
Focal Point
The point at which light rays meet to form an image.
Elliptical GalaxyMore rounded and are often longer in one direction than in the other, like a football
Irregular Galaxy
Appear to have no definite shape.
Spectral Analysis
Studying the “fingerprints” or spectral lines of elements given off by stars
Red GiantA star that has low surface temperature and a diameter that is large relative to the Sun
Super Giant
A star of very great natural luminosity and enormous size
Main SequenceContains most of the stars visible to the naked eye; stars where there is a direct relationship between brightness and size, includes our Sun
White DwarfA small whitish star of low natural brightness usually with a mass approximately equal to that of the sun but with a density many times larger
Neutron StarHypothetical dense celestial object that consists mostly of closely packed neutrons and that results from the collapse of a much larger stellar body
Black HoleA hypothetical celestial object with a gravitational field so strong that light cannot escape from it which is believed to be created in the collapse of a very massive star
SupernovaThe explosion of a very large star in which the star may reach a maximum luminosity one billion times that of the sun
H-R DiagramA chart that plots the data of stars according to their surface temperature and brightness.
Solar SystemThe Sun together with the group of celestial bodies that are held by its gravitational attraction and revolve around it
Local Group
The cluster that contains our galaxy, the Milky Way
Planet
Any of the large bodies that revolve around a star in a star system
Satellite
A celestial body orbiting another of larger size
Axis
A straight line about which a body or a geometric figure spins
SeasonsDivision of the year, based on yearly periodic changes in the weather; results from the tilt of Earth’s axis
HemisphereNorthern or southern half of the earth divided by the equator or the eastern or western half divided by a meridian
EquinoxOccurs during March and September, where all parts of Earth received equal amounts of sunlight, and the day and the night are the same length