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| Hertzsprung Russell Diagram (HR Diagram) | A graph that plots luminosity versus temperature of the stars. Size and color of the stars are usually included in most depictions of this graph. |
| Nuclear Fusion | A process that occurs when the nuclei of several different atoms combine into one larger nucleus. |
| Photosphere | The apparent surface of the star. |
| Galaxy | A huge collection of stars, gas, and dust sometimes in the shape of an elliptical, sphere, and sometimes an irregular shape. |
| Radiative Zone | A shell of cooler hydrogen above a star's core. |
| Stellar | Of or pertaining of the stars; anything related to stars. |
| Luminosity | The true brightness of an object. |
| Spectroscope | An instrument that spreads light into different wavelength so we may analyze it. |
| Parallax | The apparent change in an object's position caused by looking at it from two different points. |
| star | A ball of hot gas, primarily hydrogen and helium, that undergoes nuclear fusion. |
| Parsec | a unit of measurement used to describe distances between celestial objects, equal to 3.26 light years |
| convection zone | a layer of the Sun's interior where hot gas moves up toward the surface and cooler gas moves deeper into the interior |
| corona | The outer layer of the sun's atmosphere. Corona means crown. |
| Chromosphere | The middle layer of the sun's atmosphere |
| Core of the Sun | the most dense and hottest layer of the sun where nuclear fission takes place |
| Absolute magnitude (luminosity) | how bright a star actually is when at the same distance |
| apparent magnitude | the brightness of a star as seen from Earth; these stars are at different distances |
| Light Year (LY) | the distance that light can travel in 1 year, which is 9.46 trillion km |
| Astronomical Unit (AU) | the average distance between the earth and the sun (93 million miles) |
