What is a black hole's event horizon?

What is a pulsar?

What is the name of the process by which a star like the Sun produces energy by combining hydrogen nuclei into helium?

Which planet is famous for having a Great Red Spot, a gigantic storm system observed for centuries?

Which planet in our Solar System has the shortest day, completing one rotation in about 10 hours 33 minutes?

What is a light-year primarily a measurement of?

Which object is located at the center of our Solar System?

Which galaxy is expected to merge with the Milky Way in the distant future?