"Hypothetical H-R Diagram of a Young Cluster. In this plot titled ""M 2001 Age: 3 million years,"" the vertical axis is labeled ""Luminosity (LSun),"" and goes from 0.1 at the bottom to 100,000 at the top. The horizontal axis is labeled ""Surface Temperature (K)"", and goes from 40,000 on the left to 3,000 on the right. The zero-age main sequence is drawn as a red diagonal line starting just above 100,000 LSun at the top of the graph down to about 4000 K at the bottom. The ""Present position of Sun"" is indicated at 5500 K and 1 LSun. Over-plotted on the graph are black dots representing the individual stars in the cluster. About half of the dots lie neatly along the red line until about 10000 K and 100 LSun. At this point, the remainder of the dots lie above the red line, meaning these stars have yet to reach the main sequence."