1. Astronomy
The study of objects and matter outside the earth's atmosphere and of their physical and chemical properties

2. 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)

3. Universe
The entire celestial cosmos

4. Star
A light-radiating gaseous celestial body of great mass which produces energy by means of nuclear fusion reactions

5. Galaxy
Any of the very large groups of stars and matter that are found throughout the universe

6. System
a group of related natural objects or forces

7. Milky Way Galaxy
The galaxy of which the Sun and the solar system are a part and which contains the many stars that make up the galaxy

8. Big Bang Theory
Theory that states that the universe originated billions of years ago in an explosion from a single point of nearly infinite energy density

9. Cluster
A collection of stars or galaxies that appear close together in the sky and are gravitationally associated

10. Telescope
An optical instrument for viewing distant objects.

11. Eyepiece Lens
The lens of a telescope that makes the image larger

12. Objective Lens
The lens of a telescope that collects and focuses light

13. Spiral Galaxy
Galaxy that looks like a flat disk with a bulge in its center and spiral arms

14. Constellation
Groups of stars that seem to form patterns in the sky.

15. Polaris
The star that is above Earth’s north pole

16. Spectroscope
An instrument for forming and examining spectra.

17. Galaxy
A huge, gravitationally bound system of stars, interstellar gas and dust

18. Sun
The star in our Solar System, which all the planets orbit

19. Apparent Magnitude
A star’s brightness as it appears from Earth

20. Absolute Magnitude
A star’s actual size and temperature

21. Nebula
A cloud of gas and dust in outer space

22. Astronomical Unit
Used to measure distances within our solar system; the average distance between the Sun and the Earth; about 150 million kilometers; AU

23. Period of Revolution
The motion of the planet in its orbit around the Sun; the Earth’s revolution is 1 year

24. Period of Rotation
The time it takes for one complete spin of a planet on its axis; the Earth’s rotation is 1 day

25. Inner Planet
Mercury, Venus, Earth, Mars; much smaller and less massive than the outer planets

26. Outer Planet
Jupiter, Saturn, Uranus, Neptune; more gaseous, larger and less dense

27. Comet
A small body orbiting the Sun and occasionally exhibits an atmosphere and a tail

28. Asteroid
Chunk of rock and metal and found between the orbits of Mars and Jupiter in the asteroid belt.

29. Meteoroid
A chunk of rock that orbits the Sun

30. Meteorite
A meteoroid that has entered the Earth’s atmosphere.

31. Red Shift
A movement of the spectrum of a celestial body toward longer wavelengths that is a result of the Doppler effect

32. Focal Point
The point at which light rays meet to form an image.

33. Elliptical Galaxy
More rounded and are often longer in one direction than in the other, like a football

34. Irregular Galaxy
Appear to have no definite shape.

35. Spectral Analysis
Studying the “fingerprints” or spectral lines of elements given off by stars

36. Red Giant
A star that has low surface temperature and a diameter that is large relative to the Sun

37. Super Giant
A star of very great natural luminosity and enormous size

38. Main Sequence
Contains most of the stars visible to the naked eye; stars where there is a direct relationship between brightness and size, includes our Sun

39. White Dwarf
A 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

40. Neutron Star
Hypothetical dense celestial object that consists mostly of closely packed neutrons and that results from the collapse of a much larger stellar body

41. Black Hole
A 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

42. Supernova
The explosion of a very large star in which the star may reach a maximum luminosity one billion times that of the sun

43. H-R Diagram
A chart that plots the data of stars according to their surface temperature and brightness.

44. Solar System
The Sun together with the group of celestial bodies that are held by its gravitational attraction and revolve around it

45. Local Group
The cluster that contains our galaxy, the Milky Way

46. Planet
Any of the large bodies that revolve around a star in a star system

47. Satellite
A celestial body orbiting another of larger size

48. Axis
A straight line about which a body or a geometric figure spins

49. Seasons
Division of the year, based on yearly periodic changes in the weather; results from the tilt of Earth’s axis

50. Hemisphere
Northern or southern half of the earth divided by the equator or the eastern or western half divided by a meridian

51. Equinox
Occurs during March and September, where all parts of Earth received equal amounts of sunlight, and the day and the night are the same length