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What is an old star of average size that has begun to expand and cool as its fuel has began to run out?

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The summer has begun or has began?

The correct way to say it is "summer has begun." This is the  present perfect tense so it requires an auxiliary verb like "have"  and the past perfect conjugation of "begin"

Is the sun an average sized star?

  Yes, pretty much so. The Sun is a little larger than the "average" visible star, but not by a whole lot. However, stellar theory proposes that there may be a large num

What is A Star that has expanded and cooled?

A star that has undergone expansion, deflation and cooling is known  as a white dwarf, or degenerate dwarf. It is a small star made up  of mainly electron-degenerate matter.

What is correct - is began or is begun?

Neither is correct. "Began" is the simple past tense of "begin". The race began at 7:00. "Begun" is the past participle of "begin". Past participles are used to create the

What happens to a star when it runs out of fuel?

To start from the beginning, a stars "fuel" is initially H, or hydrogen the lightest element. A star is basically a nuclear reactor and fuses the H molecules together to form