Welcome to SkyTours with Derrick! If you've ever found yourself under the night sky wondering what that thing is, well, you've come to the right place to find out. I'll provide regular postings of just what's available for you to see at this time of this year, including planets, stars, constellations and my favorite - satellites! I'll also welcome your suggestions for what to add to the blog for your information and answer your questions.

Tuesday, November 8, 2011

Close Asteroid Pass on Nov. 8th. Feel the Breeze!

Asteroid 2005 YU 55 and the Earth-Moon System, November 8, 2011

An exciting event takes place at 6:28 p.m. EST this evening when a 400-meter long asteroid passes within 202,000 miles of Earth. This distance is about 85% of the 238,000-mile distance between Earth and the moon. While it might be a cause of concern for some, astronomers agree that the object will not come any closer to Earth and have eliminated the possibility that Earth will be struck by 2005 YU 55.

The actual trajectory of the asteroid shows it traveling from the general direction of the sun toward the Earth-Moon system, but tangent to the moon’s orbital path just inside the moon’s orbit. The moon will be almost 90 degrees from the asteroid and moving away at the time YU 55 passes and, most important, the asteroid will pass well above the orbital plane of both the Earth and the moon.

Covering nearly nine degrees of sky per hour as it passes, YU 55, comes at us from the direction of the sun and passes on out beyond us, anti-sunward toward the outer solar system. As we would see it (if we could), it will travel from west to east across the evening sky as it heads out into the deep solar system. Its orbit actually brings it around this region every 15 months or so, but current studies of its orbital path indicate no impact encounters for us over the next several hundred years.

Due to the timing of its passage, only viewers in western Europe and eastern North America have the best chance to see it.

Because of its small size and low brightness (far below naked-eye visibility), it will be difficult to see with anything less than a 6-inch telescope under dark skies. Even then, you’ll have to know exactly where to look and even if you have some skill as an observer, you may miss it.

Asteroid 2005 YU 55 was identified six years ago. When its orbit was calculated by astronomers, it was determined that YU 55 had passed even closer to earth in 1976 but at that time was unknown to exist. Since its discovery, radar measurements taken during its 2010 pass indicate its size to be rather small as asteroids go - more like a large rock rather than a ‘monster’ asteroid. During this pass scientists will examine it more closely and with better instrumentation, hoping to image finer details of the surface that may shed light on its origin.

For more information, check out the diagrams found here:


- Derrick Pitts, Chief Astronomer, Franklin Institute Science Museum, dpitts@fi.edu, 215 448 1234.