Mare Imbrium is the result of a planetesimal of 275 km across ...

[hubes95]

Mare Imbrium is the result of a planetesimal of 275 km across striking the lunar surface 4 billion years ago.
 
  a. True
  b. False
  Indicate whether the statement is true or false

Question 2

Why is there an upper end in the main sequence of the H-R diagram?
 
  What will be an ideal response?

[xthemafja]

Answer to Question 1

True

Answer to Question 2

The upper end in the main sequence of the H-R diagram shows that even if an extremely massive star does begin to form, stellar models reveal that such massive stars are unstable. To support the tremendous weight in such stars, the internal gas must be very hot, and that means it must emit floods of radiation that flow outward through the star. The resulting pressure of the radiation blows gas away from the star's surface in powerful stellar winds. The models indicate, for example, that a 60-solar- mass star sheds mass so rapidly that it can be reduced to less than 30 solar masses in only a million years.

[hubes95]

Both answers were spot on, thank you once again

[xthemafja]

Great! Please up vote