Question

We can see that stars do not appear randomly on the plot but appear to be grouped in four main regions. Most stars seem to fall into group A. It shows a general trend from cool, dim stars in the lower right corner up to hot, extremely bright stars in the top left corner. Stars in this group are called

Answer 1

Stars in this group are called Main Sequence stars.

Step-by-step explanation:

The Sun is the best example of Main sequence star. Mostly the main sequence stars are those which fuse hydrogen atoms to form helium nuclei at their cores. Stars like T Tauri, Sirius, Sirius A, Rigel etc. are main sequence stars.

As they fuse hydrogen, the trend showing from cool, dim stars in the lower right corner of the Hertzsprung-Russell diagram to hot, extremely bright stars in the top left corner of the diagram.

Most of the stars in the universe belong to Main sequence stars. Thus the stars in group A of the Hertzsprung-Russell diagram are termed as Main sequence stars.