Transcript: Japanese theorist Chushiro Hayashi did the detailed calculations to show how stars change their properties as they evolve towards the main sequence when they are still pre-main sequence stars. In terms of the HR diagram they start at regions of high luminosity and low effective temperature, few thousand Kelvin. The time taken to collapse onto the main sequence depends on the stellar mass. The highest mass stars take a shorter amount of time than the lowest mass stars. For example a fifteen times the solar mass star with an initial luminosity of thirty thousand solar luminosities takes only a hundred thousand years to reach the main sequence. A star five times the mass of the Sun with an initial luminosity three hundred times the Sun’s luminosity takes about a million years, and the Sun with an initial luminosity twenty times its present luminosity takes a few times ten to the seven years. The lowest mass stars take even longer to reach the main sequence.