The main sequence on the Hertzsprung-Russell Diagram is believed to map the aging process of the most common type of star.
Because there not that hot
The lower right part of the main sequence in the Hertzsprung-Russell diagram contains the stars that took the longest to reach the main sequence. These stars are low mass and cool, so they undergo a longer contraction phase before they start fusing hydrogen in their cores and settle onto the main sequence.
above the main-sequence stars
The main sequence - the region across the middle of the diagram.
On the main sequence.
Main sequence stars.
Because there not that hot
Of course they are on the HR diagram. They are simply not on the main sequence.
The lower right part of the main sequence in the Hertzsprung-Russell diagram contains the stars that took the longest to reach the main sequence. These stars are low mass and cool, so they undergo a longer contraction phase before they start fusing hydrogen in their cores and settle onto the main sequence.
In the HR-diagram, a diagram of color vs. luminosity, most stars are concentrated close to one curve, called the "main sequence". It turns out that stars on the main sequence are the stars that mainly get their energy by converting hydrogen into helium.
above the main-sequence stars
The main sequence - the region across the middle of the diagram.
main-sequence stars
main sequence
On the main sequence.
On such a diagram, those stars lie on a curve called the "main sequence". It is not a simple relationship - for example, it isn't a straight line on the diagram. Therefore, it isn't easy to describe in words. It's best if you look up "Main sequence", for example on the Wikipedia, and look at the corresponding diagram.
The location of a main sequence star on the H-R diagram depends on its temperature and its luminosity (or brightness). Main sequence stars follow a diagonal band on the diagram, with hotter and more luminous stars located towards the top left and cooler and less luminous stars towards the bottom right.