How Stars Work

Stars and Their Properties

Stars are massive, glowing balls of hot gases, mostly hydrogen and helium. Some stars are relatively close (the closest 30 stars are within 40 parsecs) and others are far, far away. Astronomers can measure the distance by using a method called parallax, in which the change in a star's position in the sky is measured at different times during the year. Some stars are alone in the sky, others have companions (binary stars) and some are part of large clusters containing thousands to millions of stars. Not all stars are the same. Stars come in all sizes, brightnesses, temperatures and colors.

Stars have many features that can be measured by studying the light that they emit:


  • temperature
  • spectrum or wavelengths of light emitted
  • brightness
  • luminosity
  • size (radius)
  • mass
  • movement (toward or away from us, rate of spin)

And if you're studying stars, you'll want to have these terms in your stellar vocabulary:

  • absolute magnitude - apparent magnitude of the star if it was located 10 parsecs from Earth
  • apparent magnitude - a star's brightness as observed from Earth
  • luminosity - total amount of energy emitted from a star per second
  • parsec - distance measurement (3.3 light-years, 19.8 trillion miles, 33 trillion kilometers)
  • light-year - distance measurement (6 trillion miles, 10 trillion kilometers)
  • spectrum - light of various wavelengths emitted by a star
  • solar mass - mass of the sun; 1.99 x 1030 kilograms (330,000 Earth masses)
  • solar radius - radius of the sun; 418,000 miles (696,000 kilometers)