Yes, how we wonder what you are, indeed! Today we know quite a lot about stars, even though they are so far away that they appear to us as pinpoints of light in the night sky. By the way, why do the stars appear to "twinkle"? Well, this has nothing to do with the stars themselves, although there are stars that change in brightness periodically, as we shall learn later. The twinkling of the stars that we observe on most nights is due to turbulence in the earth's atmosphere.

Simply speaking, stars are giant balls of hydrogen and helium gas, with a few other, heavier elements added to the mixture. Stars produce their own light, which is what distinguishes them from planets.  The light produced by stars is a result of nuclear reactions taking place in their cores. These reactions, in turn, are the result of the tremendous pressure inside stars, which is caused by gravitational force.

Types of stars

Stars can roughly be classified into the following types, depending on their state of evolution:

• Main sequence stars
• Red giants
• Supergiants
• White dwarfs
• Red dwarfs
• Neutron stars

A more precise, scientific classification of stars is based on spectral type. The spectral classes with corresponding colours are shown in the table below.

The Hertzsprung-Russell diagram below shows the absolute magnitude (or luminosity) plotted against spectral class (or effective temperature) of stars at different stages of evolution.

Credit: Australia Telescope Outreach and Education