On September 13-14, 2012, not one but two asteroids will sweep relatively near Earth – relatively being the operative word in a solar system where space is extremely vast in contrast to the solid bodies (like Earth) that inhabit it. Neither asteroid is going to strike Earth, or even come very near us, but both are passing close enough to be interesting. Asteroid 2012 QC8 is a one-kilometer asteroid that will pass within 23 lunar distances, or within 8.7 million kilometers. Asteroid 2012 QG42 is causing more excitement – although it is smaller at only 190-430 meters (625-1,400 ft) across – because it will pass within 7.5 lunar distances, or about 2.8 million kilometers. QG42’s closest approach will come at 05:10 UTC on September 14, 2012.

Watch asteroid 2012 QG42 online

This post will focus on 2012 QG42, an asteroid the size of a 14-story building. It will come closer and be relatively brighter than the other asteroid – but not nearly bright enough to see with the eye alone. For that reason, we provide a link at the bottom of this post for watching the passage online.

At its brightest, asteroid 2012 QG42 will have about the same brightness as the dwarf planet Pluto, which means it’ll about 1,000 times too faint to see with the eye. Backyard telescopes will have a tough time acquiring it, although many experienced backyard observers are bound to try. Large telescopes – equipped with ultra-sensitive CCD cameras, carefully set-up to point and track such a fast moving object – are a good bet for seeing it.

Watch online. With that said, the Slooh Space Camera is a good way to go. I’ve really come to trust Slooh on events like this one. Slooh will cover the near-approach of 2012 QG42 on the evening of September 13, 2012. You can watch online live on Slooh.com. The event is free to the public and starts at 4 p.m. PDT / 7 p.m. EDT / 2300 UTC.

Watch asteroid 2012 QG42 online

If you want to see it yourself through your own telescope, be sure to check out this article at Skyandtelescope.com.

Neither asteroid has any possibility of striking Earth at this pass. But both 2012 QG42 and 2012 QC8 are reminders of the dangers of close passing asteroids. According to NASA’s Jet Propulsion Laboratory – as of September 8, 2012 – astronomers have discovered 9,150 Near-Earth objects. Those are objects whose orbits sometimes bring them into close proximity with the Earth. Some 853 of these NEOs are asteroids with a diameter of approximately 1 kilometer or larger. Also, 1,328 of these NEOs have been classified as Potentially Hazardous Asteroids (PHAs).

This last group is defined as a near-Earth asteroid or comet larger than about 100 meters that can come closer to Earth than 0.05 Astronomical Units (1 A.U. = 1 Earth/sun distance). In other words, PHAs have orbits that sometimes bring them into close proximity to Earth. Plus they are of a size large enough to cause significant regional damage in the event of impact. None of the known PHAs is on a collision course with Earth at this time.

How many Potentially Hazardous Asteroids might be there? In June 2012, NASA released a survey suggesting that, so far, an estimated 20 to 30 percent of these objects have been found. The survey came from the Wide-field Infrared Survey Explorer (WISE) mission, called NEOWISE. The project sampled 107 PHAs to make predictions about the population as a whole. Findings indicate there are roughly 4,700 PHAs, plus or minus 1,500, with diameters larger than 330 feet (about 100 meters).

How many killer asteroids are out there?

By definition, Asteroid QG42 is a Potentially Hazardous Asteroid, even though it is not headed for Earth at this time. Astronomers first spotted asteroid 2012 QG42 with the Catalina Sky Survey in Arizona on August 26, 2012.

Bottom line: Potentially hazardous asteroid QG42 will come closest to Earth on the night of September 13-14, 2012. It will pass within 7.5 lunar distances, or about 2.8 million kilometers. Asteroid 2012 QC8 will also pass Earth then, coming within 23 lunar distances, or within 8.7 million kilometers. This post gives links for seeing it with a telescope, or watching the passage online.

Watch potentially hazardous asteroid 2012 QG42 online