March 20, 2019

Astro-Challenge: Spot a Near Earth Asteroid & More!

Some interesting events are afoot this last week of January into February for those who track the passage of “Low Flying Space Rocks” plus dirty snowballs across the northern hemisphere winter skies.

First up is a close pass of the Near Earth Asteroid 433 Eros. Fresh off of perihelion at a distance of 1.133 A.U. (Astronomical Units) on January 17th, this 21-mile wide (on its longest axis) asteroid passes 0.18 A.U. or 70 times the Earth-Moon distance on January 31st. The 2nd largest Earth-crosser after 1036 Ganymed, 433 Eros is also an Amor class or Mars-crossing asteroid and was the first Near Earth Asteroid to be discovered in 1898 by Carl Gustav Witt. At its closest, 433 Eros will move an apparent 3’ arc minutes per hour (a little over a degree a day) across the sky, enough to notice a nightly change against the starry background. Also, its worth noting that the “Erotian day” is about 5 hours and 16 minutes, over the course of which the oblong asteroids’ apparent brightness can vary as it tumbles end-over-end by a factor of four! 433 Eros will shine in the 8th magnitude range as it crosses from Sextans in late January into the constellation Hydra and falls below 9th magnitude in late February as it glides further south. It also has an interesting pass (within 2 degrees) near +5 magnitude Beta Sextantis on the night of January 26th-27th. The asteroid was visited twice by the Near Earth Asteroid Rendezvous (NEAR)-Shoemaker spacecraft, once during a flyby in 1998 and for a year-long orbit starting in 2001. Fans of Orson Scott Card may also remember 433 Eros as the setting for the Command School in his novel Ender’s Game.

The path of 433 Eros through February 2012. (Created by the author in Starry Night).

Do make an attempt to spot 433 Eros this year, as the last close passage was in 1975 & the next good passage isn’t until 2056! A good project would be to photograph it against targeted star fields on successive nights, or perhaps just sketch the area at moderate power and watch for the moving “star” from night to night. Sky & Telescope has an excellent article on finding Eros, and Heavens-Above is another great place to check for its current position.

In other asteroid news, 1746 Brouwer occults a +7th magnitude star on the morning of January 30th at 01:18 UT (8:18PM EST on the 29th) for observers along a path from SE Canada and the Great Lakes region to southern New England. Observers may see the star “wink” out for up to 4 seconds in duration. The target star HIP 12184 will also be easily identifiable as it’s a wide (38”) double, handy for visual acquisition.

A fine photo op will also present itself as Comet C/2009 P1 Garradd passes within ˝° degree of the fine globular cluster M92 in the constellation Hercules on February 2nd-3rd. Comet Garradd has been a solid 7th-8th magnitude performer throughout the Fall of 2011 and should be an easy binocular object high in the morning sky throughout February. It reaches its nearest to Earth on March 5th at a distance of 1.27 AU, and stands only 19 degrees from the northern celestial pole on March 11th, making it a circumpolar target for much of the northern hemisphere starting next month.

Finally, February 2012 is not only a leap year, but it is also a month that’s “missing a Moon phase” as reckoned in Universal Time… that is, the First Quarter Moon occurs just an hour and 21 minutes into March 1st. February is the only month that can be missing one of the traditional four phases (New, 1st Quarter, Full, & Last Quarter) because it’s the only month shorter than our friend, the synodic period which is the span of time that it takes for the Moon to return to the same phase (i.e. New to New, Full to Full, etc). An average synodic period is 29 days, 12 hours, and 44 minutes 2.9 seconds long, although perturbations can make the actual period range between 29.18 and 29.93 days. For this unique quirk of our calendar to occur, any of the aforementioned  phases needs to  first fall on January 30 or 31st; as you can see, the window for this to happen is narrower still on a leap year, when February has 29 days!

Just how rare is this occurrence? Well, the last February missing a Moon phase was in 1999, and the last Leap year missing one was 1940… the next year containing a February missing a Moon phase is 2014, and the next leap year won’t be until 2052 A.D.!