Temperature and Luminosity Like size, the temperatures and luminosities of main sequence stars increase with increasing mass. The most massive main sequence stars have surface temperatures of about 50,000 K and are spectral type O3. The main sequence stars of lowest mass have temperatures of only 2400 K and are spectral type M8. Notice that although the most massive main sequence stars are 750 times more massive and 150 times larger than the least massive main sequence stars, the most massive stars are only about 20 times hotter than the least massive stars. The Sun, which has a temperature of 5900 K and is spectral type G2, is near the middle of the range of temperatures for main sequence stars.