It's not entirely accurate to say there are only four main types of stars. Astronomers classify stars based on many factors, including temperature, size, luminosity, and chemical composition.

However, we can group stars into broad categories based on their spectral class, which is related to their surface temperature:

1. O-type stars: The hottest and most massive stars, with surface temperatures exceeding 25,000 Kelvin. They are blue-white in color and have very short lifespans.

2. B-type stars: Still very hot and massive, these stars have surface temperatures between 10,000 and 25,000 Kelvin. They appear blue-white.

3. A-type stars: Cooler than B-type stars, these stars have temperatures between 7,500 and 10,000 Kelvin. They are white in color.

4. F-type stars: With surface temperatures between 6,000 and 7,500 Kelvin, these stars are yellow-white in color. Our Sun is an F-type star.

5. G-type stars: Similar to our Sun, these stars have temperatures between 5,200 and 6,000 Kelvin. They are yellow in color.

6. K-type stars: Cooler than G-type stars, with temperatures between 3,500 and 5,200 Kelvin. They are orange in color.

7. M-type stars: The coolest and most common stars, with surface temperatures below 3,500 Kelvin. They are red in color.

It's important to remember that these are just broad categories, and there are many variations within each type. For instance, red giants and supergiants are much larger and more luminous than typical M-type stars, while white dwarfs are much smaller and denser.