Main Sequence
A series of star types in which most stars belong, represented on the HR (Hertzsprung-Russell) diagram
Protostar
A baby star, an area of material that hasn't yet formed into a fully-fledged star
White Dwarf
A small, white very dense star that is formed when a low-mass star has exhausted all its central nuclear fuel and lost its outer layers as a planetary nebula
Sun
The star around which the earth orbits
Luminosity
The brightness of an object
HR Diagram
A scatter graph of stars showing the relationship between the stars' absolute magnitudes or luminosities versus their spectral classifications or temperatures
Red Giant
A very large star of high luminosity and low surface temperature.
Supernova
A star that suddenly increases greatly in brightness after a catastrophic explosion that ejects most of its mass
Neutron Star
An extremely dense, compact star composed primarily of neutrons, especially the collapsed core of a supernova
Black Hole
A massive singularity formed at the beginning of the universe or by the gravitational collapse of a star exploding as a supernova whose gravitational field is so intense that nothing can escape
Nebula
A cloud of gas and dust in outer space; place where all stars are born
Red Supergiant
An aging giant star that has consumed its core's supply of hydrogen fuel
Planetary Nebula
a ring-shaped nebula formed by an expanding shell of gas around an aging star
Red Dwarf
A small, old, red, relatively cold star
Light years
A unit of measurement equivalent to the distance that light travels in a year
Galaxy
A large grouping of stars in space
Spiral Galaxy
A galaxy with a bulge in the center and very distinct long arms winding around the center
Elliptical Galaxy
A galaxy with a long oval shape, a bright center, no apparent internal structure or spiral arms, and very little dust or gas
Irregular Galaxy
A galaxy with very little symmetry the does not fit into any category
Lenticular Galaxy
Galaxy with a central bulge or bar with short arms, if any are present