First it’s a Supermoon, then Halloween fireballs hurtling from Taurus and now this — a chunky asteroid that will zip only a little farther than the moon from Earth overnight. Actual time of closest approach by the near-Earth asteroid 2015 TB145 occurs tomorrow morning around noon Central Daylight Time, but if you have a 6-inch or larger telescope, you’ll have a shot at seeing this recent discovery late tonight and before dawn tomorrow.
TB145’s all of 1,300 feet (400 meters) across and will pass us at a distance of 300,000 miles (480,000 km), making it large and close enough to brighten to magnitude +10. Even a small 4.5 inch scope would be able to manage that were it not for the waning gibbous moon nearby for much of the night. The asteroid rises in Orion’s Shield around 10:30 p.m. local time and becomes well-placed for viewing around 11:30-midnight. At that time, an 8-inch scope should show it, but don’t let me scare you off from trying your 4.5-inch on it, especially at the start of dawn.
This speedy, aircraft carrier-sized boulder steadily brightens as it approaches the Earth, rising to around magnitude +10 by Halloween dawn, when Taurus (it’s home at that hour) has tilted over into the western sky. TB145 poses no danger to the planet and will blast out of here in a hurry. Come tomorrow evening, it will have have grown so faint (17th magnitude), only cameras or those with very large telescopes will pick it up.
That’s why tonight’s the night. I’ve included several maps for observers in the western hemisphere and specifically the United States. They’re hand-plotted based on the latest orbital elements (numbers describing an asteroid’s orbit) and show TB145’s accelerating path across Orion and Taurus starting around midnight tonight (Oct. 30-31) and continuing through the early morning hours.
Because the asteroid approaches Earth so closely, its path against the starry backdrop shifts depending on where you live. Three of the maps show its path for observers in the north central U.S. A fourth map is drawn for the south central U.S, so you can see how much the path shifts. It isn’t much — about 5 arc minutes or 1/6th the apparent size of the full moon — but it’s noticeable. Keep that in mind if you plan to observe this speed demon. Yes, it will be bookin’. Around midnight-1 a.m., TB145 covers about 3° of sky per hour. That doubles by early dawn and expands to around 10° per hour during closest approach. Even at 3° an hour, that’s 1/10th of a “full moon” every minute! Watch closely and you should be able to see it move in real time.
Because of the path shift depending on location, pick a time you want to observe and arrive there 5 minutes in advance. Study and lightly memorize the star field the asteroid will pass through. “Camp” there a while and wait for a “moving star” to make an appearance. That’ll be TB145 doing what asteroids do best – pretending to be stars! I’d suggest after you print out the maps to draw a line connecting the dots, so you have a nice track to sight along. I wasn’t able to do this due to software issues.
Nice video on how astronomers plan to ping the asteroid with radar to create images and study its surface
For more information, especially on how to create your own customized charts for a particular location, please see my earlier article in Universe Today. Hit by bad weather? Don’t have a scope? Check out Gianluca Masi’s live webcast on his Virtual Telescope site starting this evening at 7 p.m. CDT (0 UT) Oct. 30-31. Let us know if you have success (or not) finding this latest near-Earth asteroid. Good luck!