Author Question: When does a protostar become a main-sequence star? A) when the rate of hydrogen fusion becomes ... (Read 66 times)

RRMR · **on:** Jul 27, 2018

When does a protostar become a main-sequence star?

A) when the rate of hydrogen fusion becomes high enough to balance the rate at which the star radiates energy into space
B) when a piece of a molecular cloud first begins to contract into a star
C) when it becomes luminous enough to emit thermal radiation
D) at the instant that the first hydrogen fusion reactions occur in the protostar's core

Question 2

Which of the following is not evidence supporting the giant impact theory for the formation of the Moon?

A) Computer simulations show that the Moon could really have formed in this way.
B) The composition of the Moon is similar to that of Earth's outer layers.
C) The Moon is depleted of easily vaporized materials, as we would expect from the heat of an impact.
D) Scientists have found several meteorites that appear to be the remains of the object that caused the giant impact.
E) We see signatures of giant impacts on other planets.