Universe

You are advised to research NASA and major university Astronomy department to get detail answers.

Below are only "earthly" answers for casual review:

1
Stars are mainly gas thermal reaction of fission (separation of gas molecules expands) or fusion (combination of gas molecules contracts) in balance (not always equal) in sustaining the thermal reaction of the star will determine when the star expands or contracts.

2
When the star "burning" more gases than combine to maintain the thermal balance, the burned gases expands and the heat of the thermal balance reduces, thus the star "perimeter" becomes bigger and "less hot" (turning red from bright white).

3
As the gas burning reaction of the star expands to it maximum and the last of the explosion reaction occurs.

4
Stars of the far is move away from us (in all directions), so the contents (stars/planets) in the universe is moving away from each other.
Move back in time, the contents of the universe comes toward each other in space, they must have converged to "a point" to begin with. This point of begining of the expansion will be the beginning of the universe call "Big Bang", assuming it starts by an "explosion".

5
The age of the universe is based on the "Big Bang" theory deducing the time backward from the time of expansion from measuring the exsiting stars moving rate away from each other. It is uncertain the rate of the past is the same as the existing rate. The rate of expansion at the beginning may be must faster than now and unable to accurate predict what is the rate in the very very long time ago.

6
A rover on the surface of planet can investigate the compositions of soil, rock, air, or magnetic, thermal and geographic characteristics of the planet.

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