In the critical density universe now proposed, the dark energy makes up about what percent of all of the energy in universe?

An object that failed to become a star due to its small mass is called

Venus is the only planet that rotates in a reverse direction compared with the rest of the planets in our Solar System.  What is the most likely cause for Venus’s unusual rotation?

The surface layer of our Sun is called

Which process below drives plate tectonics on the surface of Earth?

A photon takes about a million years to escape from the solar core.  How long does it take for a neutrino to escape?

Which of the following terms describe an average distance between Sun and Earth?

What is Ptolemy’s epicycle supposed to explain?

What are the zodiacal constellations in Astronomy?

 Dorsal is the top of this picture and ventral is at the bottom.  What is the structure labeled “A”?