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 | | Centaurus A | by jimkster on Flickr |
| - A star is a massive, luminous sphere of plasma held together by gravity.
- At the end of its lifetime, a star can also contain proportion of degenerate matter.
- The nearest star to earth is our sun, which is the source of most of the energy on Earth.
- Other stars are also visible at night, and some of the stars may have died out and the light is just still traveling towards us.
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 | | Abell 1689: A Galaxy Cluster Makes Its Mark (A galaxy cluster at a distance of about 2.3 billion light years from Earth.) | by Smithsonian Institution on Flickr |
| - For at least a portion of its life, a star shines due to thermonuclear fusion of hydrogen in its core releasing energy that traverses the stars interior and then radiates into outer space.
- Almost all naturally occurring elements heavier then helium were created by stars, sometimes by a supernova which occurs when a star explodes.
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 | | Free space fantasy universe time warp pulsar texture for layers | by Pink Sherbet Photography on Flickr |
| - Astronomers can determine the mass, age, chemical composition, and many other properties of a star by observing its, spectrum, luminosity, and motion through space.
- The total mass of a star is the principal determinant in its evolution and eventual fate.
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 | | Ecliptic Star Trails | by makelessnoise on Flickr |
| - Other characteristics of a star are determined by its evolutional history, including diameter, rotation, movement, and temperature.
- A plot of the temperature of many stars against their luminosities, known as a Hertzsprung-Russel diagram (or H-R diagram) allows the age and evolutionary state of a star to be determined.
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