2005 YU55: See it when it passes Earth on November 8 and 9

It’s coming! Large asteroid 2005 YU55 – the largest close-approaching asteroid on record – will sweep closest to Earth tomorrow (November 8, 2011) at 5:28 p.m. CST (23:28 UTC). About a quarter mile wide (400 meters) – round and dark – 2005 YU55 will be 198,000 miles (319,000 kilometers) from Earth’s surface. It will be closer than the orbit of the moon. What will it look like? Will you see it as it sweeps past?

More details about asteroid 2005 YU55

Unless you are (or know) an amateur or professional astronomer, with access to at least a 6-inch telescope, the answer is that you will not see it. The asteroid is some 8,700 times smaller in diameter than the moon. It will be too faint to see with the eye alone, or even binoculars. If you could see it, this asteroid – albeit close to Earth – would look like a steadily moving star. It will not show a disk, as the moon does.

A few hours after passing closest to us, the asteroid will peak in brightness at magnitude 11.1. That’s roughly 100 times fainter than the limit of human vision.

However, if the weather cooperates, those with telescopes will sure be watching for 2005 YU55, and some will spot it.

According to Sky & Telescope magazine, the asteroid’s track past Earth is especially favorable for western Europe and North America. But you’ll need to know exactly where and when to look. According to Sky & Tel:

… the object will traverse the 70° of sky eastward across several constellations, from Aquila to Pegasus, in just 10 hours. And light from a nearly full moon will brighten the entire sky somewhat, making faint stars and the asteroid somewhat more difficult to spot.

Sky & Telescope’s editors have prepared two detailed finder charts. The first gives a general sense of where to look.

Okay, here’s the first chart, above. If you aren’t a stargazing, it’ll look confusing to you. But what it’s showing is pretty simple. It’s showing that 2005 YU55 will cross many constellation boundaries in our sky as it sweeps near us on November 8 and 9. That said, the asteroid will not sweep across the sky as fast as a meteor (aka a “shooting star”) does. Instead, it’ll travel along steadily, moving at times in front of the background stars at 7 arcseconds per second. That means it will cover a moon’s width of sky in under 5 minutes.

The second Sky & Telescope chart, above, provides a detailed view that amateur astronomers will use while outside with their telescopes. It shows the path of asteroid 2005 YU55 just over an hour on November 8 for North America, from 1:51 to 3:12 Universal Time on November 9. Translate Universal Time to your time zone. North is up; east is left. On each of the little upside-down maps of the U.S., put a pencil dot on your location. These are the asteroid’s apparent positions at 2:00 and 3:00 UT for your site. Connect your dots with a straight line paralleling the line plotted, which is for Kansas. Sky & Tel editors say:

Once you’ve aimed at exactly the right spot, you shouldn’t have much trouble telling which starlike point is 2005 YU55. It will be gliding fast enough to move along in real time as you watch using a moderately high-magnification eyepiece.

In other words, because it’ll be so close to us, not everyone on Earth will see the asteroid in exactly the same place among the stars. Alan MacRobert, a longtime editor at Sky & Telescope and a skywatching expert explains:

As it passes Earth, the asteroid gets so close that its position among the stars will be significantly affected by your location. So the magazine’s detailed finder chart takes this parallax effect into account, by including small upside-down maps of the United States that permit you to establish the correct path for your location.

Bottom line: We’ve had many questions from people about how to see asteroid 2005 YU55 as it sweeps closest to Earth on November 8, 2011. This asteroid will come within 200,000 miles (319,000 kilometers) from Earth, and although it is a large asteroid, it is small in contrast to the Earth or moon. Thus it will be faint – too faint to see with the eye alone. You will need at least a 6-inch telescope to see it. That said, this post provides two charts from Sky & Telescope magazine that should help you find the asteroid, if you do have telescopic aid.

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