The comet will reach its closest approach at 2:28 pm EDT (11:28 am PDT) when it will be about 87,000 miles from Mars. If the comet were passing by Earth instead of Mars, it would be closer to the surface than our moon

The Oort Cloud is made up of billions of comets.

Comet Siding Spring will be the first comet from the Oort Cloud to come near enough for us to take close-up observations of it with spacecraft — especially those around Mars. 

"We can't get to an Oort Cloud comet with our current rockets," said senior astrophysicist at the Johns Hopkins University Applied Physics Laboratory during a NASA news conference last week. In a way, it's a "free flyby" that will give scientists the chance to learn more about the very early stages of our solar system and how the planets formed.

Slooh will be hosting two shows of the event: The first show "Close Call — Comet Siding Spring zips by Mars" will begin at 2:15 EDT (11:15 PDT). The second show "Comet Siding Spring — The Outcome" will start at 8:30 pm EDT (5:30 pm PDT). You can watch both shows live on Slooh's website or right here. 

For more on this story and video go to: http://www.businessinsider.com/watch-livestream-comet-skim-mars-oct-19-2014-10#ixzz3GbyZgJZN