Image of a crescent 2005 YU55 constructed using Arecibo radar on its 2010 passage.
A large Near Earth Asteroid (NEA) makes an approach this week closer than our Moon, and with a little luck and skill, you may just be able to spy it. The object in question is 2005 YU55, an Apollo asteroid about 400 meters in diameter. Discovered in 2005 from the Steward observatory in Arizona, this asteroid is on a 446 day orbit that takes it to a perihelion passage just inside the orbit of Venus at 0.65 Astronomical Units (A.U.) and very near the orbit of Mars at an aphelion of 1.63 A.U. This sets this asteroid up for several close planetary encounters, one of which will occur Tuesday, November 8th as 2005 YU55 passes within 80% of the Earth-Moon distance. The last time an asteroid this large passed our fair planet was the passage of 2010 XC15 in 1976 at 50% the distance to the Moon, but as its name indicates, it hadn’t been discovered yet, and hence that particular passage went unobserved!
Despite all the hoopla that being generated around 2005 YU55, there is no chance that it will hit the Earth (or the Moon) on this pass or any in the foreseeable future. 2005 YU55 was rated a “1” on the Torino scale in 2010, marking it as an Earth crosser “that poses no unusual level of danger.” Several campaigns are planned to observe the passage of the asteroid, including plans to once again map it with the radar from Arecibo and Goldstone, as was done previous on the more distant April 2010 pass.
But YOU landed on this page because you want to see the asteroid as it whizzes by with your own eyes, right? That’s the question we get the most frequently, right behind “Will it hit us?” Visually tracking a Near-Earth asteroid can be thrilling to watch; for example, I’ve actually seen 4179 Toutatis years ago show discernable movement after tracking it for a few moments in the eyepiece!
Wide field finder of 2005 YU55 from sunset until 8:30PM EST.
(Graphics created by Author using Starry Night & Paint).
But first, the bad news; 2005 YU55 won’t break a visual magnitude of +10; you’ll need a good sized telescope and dark skies to track it. Strike #2; the Moon will be only two days away from Full on the night of the 8th, and the faint asteroid will be headed in its general (but non-impacting) direction in the sky….
But all is not lost. Closest approach to Earth occurs at 11:29 UTC/06:29 EST at about 202,000 miles distant, placing it high to the south west for observers on the US Eastern Seaboard. (Don’t forget to “fall back” to Standard time on Sunday, November 6th; you wouldn’t want to miss seeing the asteroid because of an anachronistic convention, but I digress..) At its closest approach, 2005 YU55 will glide along at one degree every 7 minutes, easily noticeable after a few minutes of observation at low power. I plan to target selected areas with my GOTO mount, sketch the field, then watch for changes. I may also take some wide-field piggyback stills with the DSLR, but mostly, this one will just be fun to watch. The asteroid will pass through the constellations Aquila, Delphinus, and Pegasus as it heads westward. Interestingly, 2005 YU55 passes within a degree of Altair centered on 6:07:30PM EST only 27 minutes after local sunset, and also makes a very close pass of the star Epsilon Delphini during closest approach. These both make good visual “anchors” to aim your scope at during the appointed time and watch. Keep in mind, the charts provided are rough and “Tampa Bay-centric…” on an approach as close as this one, two factors muddle the precise prediction coordinates of the asteroid; one is the fact the gravitational field of the Earth will change the orbit of 2005 YU55 slightly, and two is that the position will change due to the position of the observer on the Earth and the effect of parallactic shift. Many prediction programs assume the Earthly vantage as a mere point in space, fine for positioning deep sky objects but not so hot for ones passing near the planet. A good place to get updated coordinates is JPL Horizons website which lets you generate an accurate ephemeris for your exact longitude latitude and elevation.
As noted, 2005 YU55 will pass our Moon at 8 AM Universal Time on November 9th at a distance only marginally closer than it did the Earth, at 140,000 miles. Interestingly, it also transited Sun on November 3rd as seen from the Moon, but would have appeared <1” in size, a tough target for any would-be lunar-based observer. It next close predicted passage of the Earth won’t be until 2056 at nearly 3 times the distance. The next known large asteroid to make a close pass our planet is 2001 WN5 passing 154,000 miles distant in 2028. Later the next year, 2005 YU55 will have a close (180,000 mile) passage of Venus, again altering its orbit slightly for future apparitions.
Studying NEO’s such as 2005 YU55 is a worthwhile endeavor, as we may be mounting a manned mission to one in the coming decades. These would serve as prime “stepping stones” (pun intended) to get us back out into the solar system, and of course, it’s always handy to know just how well these things are put together, should we need to deflect one. Their formation and composition may also provide clues to the formation of the primordial solar system. This Tuesday, make an effort to get out with that backyard light bucket that your neighbors think is a canon and show them this interloper passing through our Earth-Moon neighborhood!