Classification of Stars According to Color
- A star's color is related to its surface temperature.
- The Sun has a surface temperature of approximately 5778 K and is yellow in color.
Brightness of Star
- Brightness of star is determined by many factors such as size, temperature, and amount of energy release.
- Apparent magnitude
- The brightness of a star if observed from the Earth is also dependent on its distance from the Earth.
Stars that are closer to the Earth seem brighter compared to stars far away from Earth.
- The apparent magnitude is not a good measure of the actual brightness of the star.
- For example, even if star A is actually brighter than star B, star B may look brighter from the Earth because star B is close to the Earth while A is far away from the Earth.
- Absolute magnitude
- To figure out the actual brightness of the star, we use absolute magnitude.
- Absolute magnitude is the brightness of a star if it were at a standard distance from the Earth. Absolute magnitude is independent of the star's distance from the Earth.
- The standard distance is 10 parsecs, or 32.6 light years.
- If star A and star B were both 10 parsecs away from the Earth, star A is brighter than star B. We can find out the actual brightness of the star!
- Plots the temperature of stars against luminosity (or absolute magnitude)
- Main sequence stars occupy the diagonal area of the HR diagram
- Every star goes through a specific evolutionary stage, which corresponds to a change in temperature and brightness. Each evolutionary stage can be shown as movement to different areas of the HR diagram.