October 19, 2017

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 ½° 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.!

The Passage of Asteroid 2005 YU55 & How to See It.

Image of a crescent 2005 YU55 constructed using Arecibo radar on its 2010 passage.

(Credit: NASA/Cornell/Arecibo).

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.

Passage of of 2005 YU55 near Altair from 06:03PM-06:12PM EST. (Note: may be up to a degree off center for different geographic locations).

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!


November 2011: Life in the Astro-Blogosphere.

A “Warhol Moon!” (Photo mosaic by Author).

Wow, can you believe that 2011 is coming to a close? It seems that it was only yesterday that we where installing Windows 98 and fretting about Y2K, and now we have a decade plus of the 21st century under our belts… this month brings a pair of launches headed towards the Red Planet, a partial solar eclipse for distant lands, and a Tweetup for one of the aforementioned launches: [Read more...]

14.05.11: Finding NASA’s NEEMO.

“Aqua-nauts” at work on NEEMO. (Credit: NASA).

A mission to a Near-Earth Asteroid will be unlike any other that NASA has undertaken to date. Gravity will be negligible, and astronauts will have to work in an unknown environment far from Earth. To this end, NASA has begun set-up earlier this week of an exciting new project off of the Florida Keys. [Read more...]

09.04.11: 2010 SO16-A World in a Bizzaro Orbit.

A horseshoe orbit. (Credit: NASA).

Ever wondered what local space would be like if the Earth had more than one moon? Well, it turns out that we do have several natural interlopers; sort of. Recently, researchers A.A. Christou and D. J. Asher of Armagh Observatory in Northern Ireland reported on the discovery of a unique Near-Earth Asteroid (NEA): 2010 SO16, a 200-400 meter space rock locked in a horse-shoe orbit with Earth. [Read more...]

27.04.10-Does Planetary Gravity “Stir up” Asteroids?

(Credit: Hayabusa/JAXA).

(Credit: Hayabusa/JAXA).

 The bizzare world of Itokawa as seen from Hayabusa.

   Asteroids are probably the most intriguing bodies in our solar system. More than just errant chucks of rock, these tiny worlds may hold the key to early planetary accretion. Several mysteries about these bodies persist; are they single slabs of rock, or loosely held together rubble piles? The question may be more than just an academic one, especially if we want to move one of these celestial missiles headed our way. Now, researcher Rick Binzel of MIT has noted a curious factor about many Near Earth Asteroids (NEA’s); nearly all which have experienced close passages near the Earth have seemed to undergo a spectral change. Specifically, the study looked at simulations of the orbits of 95 NEAs. Most are of the S-type, showing a reddish, sun burnt spectrum indicative of solar wind blasting for several million years. About 20, however, show a Q-type resurfacing, as if they had been “freshened up” somehow. Q-type asteroids are of the same spectral class as ordinary chondrite meteorites found on Earth, and are almost never observed in the main asteroid belt. Tracing back their orbits, all 20 show evidence of passages closer to the Earth than our Moon sometime in their history. Scientist Pierre Vernazza of the European Space Agency estimates that asteroids can be reddened by solar wind exposure in about one million years. Looking at asteroids such as 25143 Itokawa imaged by the Japanese Space Agencies’ Hayabusa spacecraft, one can easily imagine such a loose collection of rock experiencing massive landslides as it passes the massive Earth. Such an event may even splinter the main body, as happened to comet Shoemaker-Levy 9 in 1992 when it was torn apart and ultimately impacted Jupiter. And we have an unprecedented opportunity to study an NEA in 2029, when asteroid 99942 Apophis swings by Earth at a distance of about 20,000 miles above our surface. “My vision is that we would have (Apophis) all wired up and monitored so that we can listen to it creak and groan as it flies by,” says Binzel. Knowing what kind of shifting terrain they face might also be of vital importance to future visiting astronauts. A mission to such a body was stated by president Obama in a recent address given at the Kennedy Space Center. Clearly, these bodies are of unparalleled interest… all eyes will be on the Australian desert on June 13th of this year as Hayabusa returns to Earth. Did it successfully grab a sample of an NEA? Researchers won’t know for sure until they have the sample return canister in hand!