The method used by Hubble to determine the distance to the Andromeda galaxy was

Label the layers of the Earth’s atmosphere using the diagram below

The least dense planet in the solar system is

The letters G U T  from the GUT Era stand for Grand Unified Theory. This theory explains how 3 of the fundamental forces are indistinguishable. Which three forces does it describe?

Which of the following lists contain all terrestrial planets?

Which of the following is evidence that the Earth orbits around the Sun?

What was the age of the universe when it became transparent and photons could travel without running into anything?

Which is the classification given to a galaxy with a small nuclear bulge, and loosely wound arms with no bar through the nuclear bulge?  

The composition of Saturn’s rings are

What percentage of visible matter is made of Hydrogen?