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Main Sequence Stars

Main sequence stars are more or less ordinary stars. Most stars are on the main sequence, and they spend most of their lives there uneventfully. The Sun is one such star.
Before describing these stars in-depth, we need to locate them on what’s called the Hertzsprung-Russell diagram!

Hertzsprung-Russell Diagram

The Hertzsprung-Russell diagram (or the HR Diagram) is a two-dimensional graph that plots all types of stars together in a single graph. It does this according to color/temperature and brightness. Color is plotted on the x-axis from blue to red, and luminosity is plotted on the y-axis from dim to bright. A dot on the diagram represents an individual star.
Hertzsprung-Russel Chart

Hertzsprung-Russell diagram is a scatter plot of stars representing the relationship between brightness and color/temperature. Credit: Image created by the European Southern Observatory.

On the diagram, have you noticed that there is a series of dots, which can form a straight line? The straight line starts from the upper left of the diagram to bottom right. This straight line is the “main sequence”, and all the stars on this line are main sequence stars.

The Sun and Other Main Sequence Stars

The Sun is a main sequence star, and it is a yellow dwarf. It has been a main sequence star for about 5 billion years. Most stars throughout the Universe are also on the main sequence. This has to do with the age of the Universe. It’s not yet old enough for most stars to have evolved off of the sequence. 
The sun is a main sequence star.

The sun is a main sequence star, and it is the closest main sequence star to the Earth.

Similar to all living things, stars also have different life stages. Main sequence star describes the adulthood phase of a star’s life. When a star starts converting hydrogen into helium and releasing energy, its main sequence phase begins. This process describes the adulthood of a star and will last until this process stops.
Stars spend approximately 90% of their life in the main sequence phase. Main sequence stars are classified in seven categories O-B-A-F-G-K-M. Stars from an identical category share similarities in properties. This includes mass, luminosity, size, temperature, color, and lifetime.
To wrap up, here is a great lecture that introduces some facts about main sequence stars. This video also introduces other topics such as the HR diagram, star classification, and properties of stars.

Other Great Resources:

Crash Course Astronomy on Stars: 

Written by ChungLing Wong.