Question

How often is Halley's Comet visible from Earth?
Every 17 years
Every 100 years
Every 20-30 years
Every 75-76 years

Answer 1

I think I'm stalking your questions now. e_e (jk)
http://www.space.com/19878-halleys-comet.html

Answer 2

"Halley's Comet is arguably the most famous comet. It is a "periodic" comet and returns to Earth's vicinity about every 75 years" So every 75-76 years.

Answer 3

Thank you.

Answer 4

You're welcome (sorry that was late) :]

Answer 5

thank gaben ;^)

Answer 6

dot.