Asteroid 2012 DA14: Observing Prospects and How to See It

2012-DA14
Image credit: NASA/JPL-CALTech

Mark your calendars: this Friday, February 15, 2013, is the close flyby of Near Earth Asteroid 2012 DA14, passing just 27,630 kilometers (17,168 miles) from the surface of the Earth. About 50 meters (164 feet) in size, 2012 DA14 and its close shave marks the the first time there has been passage of an asteroid this close that we’ve known a year beforehand. Yes, it passes within the ring of geosynchronous satellites girdling the Earth. No, there’s no danger, either to said satellites or the Earth, so Bruce Willis can stay home for this one.  But right behind those inquiries, the question we most frequently get is… how can I see it?

The orbital path of asteroid 2012  DA14 as seen face on (top) & near edge on (bottom). (Credit: JPL Small Body Database Browser).
The orbital path of asteroid 2012 DA14 as seen face on (top) & near edge on (bottom). (Credit: JPL Small Body Database Browser).

The great news is that an advanced observer can indeed catch 2012 DA14 on its close pass the night of February 15th… with a little skill and luck. Now for the bad news; the asteroid won’t be visible without binoculars or a telescope, and North America will largely miss out.

2012 DA14 will be really moving across the sky on closest approach, covering 0.8° per minute, or the diameter of a Full Moon every 45 seconds!  With its passage closer to the Earth than the ring of geosynchronous satellites, it’s worth treating the passage of the asteroid as a satellite and hunting it down accordingly. Catching and watching such a pass can be an unforgettable experience; not many objects in the sky show such swift motion in real time. In fact, 2012 DA14 will span the celestial sphere from declination -60° to +60° in just 4 hours!  Needless to say, its passage through the Earth’s gravity well will alter its orbit considerably; most planetarium software programs do not account for this and thus will introduce a large error for a heliocentric object. Compounding the dilemma is the large amount of parallactic shift of such a nearby object. As viewed from the span of the Earth, 2012 DA14 will have a parallax of ~20° at greatest approach!

The path of asteroid 2012 DA14 through the celestial sphere on February 15th. (Created by Author).
The path of asteroid 2012 DA14 through the celestial sphere on February 15th. (Created by Author).

But two sites on the web can help you with the search. One is Heavens-Above,  which currently has a link on its main page to custom generate sky charts for specific locations for 2012 DA14 (make sure you’re logged in as a registered user and your observing location is set correctly). Another option is to generate an ephemeris customized for your location from the JPL Solar System Dynamics Horizons Web-Interface.

Asteroid 2012 DA14 is approaching the planet Earth from “down under,” and moving almost exactly parallel to the 12 hour line in right ascension. In fact, it’ll cross very near the equinoctial point in Virgo (one of the two points where the celestial equator and the ecliptic cross) shortly after its closest approach on Friday, February 15th at 19:25UT. The asteroid will be at the local zenith (straight overhead) for observers in the pre-dawn hours located in western Indonesia at closest approach. Australia and eastern Asia will have a shot at seeing the asteroid as it whizzes through the sky in the early morning hours of February 16th local. Observers in western Asia, Africa and Europe will see the asteroid lower to the east on the night of the 15th. Note that 2012 DA14 juuuuuust misses Earth’s shadow (see strip chart) at closest approach. The shadow of our fair planet is ~20° across at the distance of the geosynchronous satellites; had it passed about a month later, we would have seen an “asteroid eclipse!” In fact, “eclipse season” for geosynchronous satellites occurs right around the equinoxes and is only a month away.

The “banana strip chart” shows the path of 2012 DA14 from the time it reaches a magnitude brighter than +10 at 17:40UT until it dips back down below it at 22:10UT on the same night. It also shows the width of uncertainty for its position due to the aforementioned 20° of parallax, and the points that it enters and departs the distance sphere of the geosynchronous satellites. Keep in mind, these satellites still orbit roughly hundred times higher than the International Space Station!

A good search strategy to catch 2012 DA14 is to actually to treat it like you’re hunting for a faint satellite. Find the time that it’s crossing a set declination and begin scanning with binoculars in right ascension back and forth until you “ambush” your astronomical prey moving slowly against the starry background. If using a telescope, use the lowest power and widest field of view that the instrument will allow. We’ve used this technique in the past to sweep up Near Earth Asteroids 2005 YU55 and 99942 Apophis and routinely use it to hunt for satellites fainter than naked eye visibility. At closest approach, asteroid 2012 DA14 will shine at around +8th magnitude as it crosses the Bowl of Virgo northward past Denebola in the constellation Leo.

Recent measurements early this month conducted by astronomers at the Las Campanas observatory in Chile refined the orbit of 2012 DA14, placing its February 15th passage just 45 kilometres closer to Earth than previously calculated but still well outside the threat zone. Campaigns are underway to refine measurements of its orbit even further on this pass. We won’t get another close pass of 2012 DA14 until February 16th, 2046 when the asteroid misses us at about twice the distance of the Moon. An impact has been ruled out for this century. Predictions get less certain the further you project them into time, and 2012 DA14 will definitely be a space rock worth keeping tabs on!     

Mercury’s False Moon: The Mercury/Mars Planetary Conjunction this Weekend

Mercury and Mars on February 8, 2013. See how close they'll be? Image credit: Stellarium.

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The history of astronomy is littered with astronomical objects in the solar system that have fallen to the wayside. These include fleeting sightings of Venusian moons, inter-mercurial planets, and even secondary moons of the Earth.

While none of these observations ever amounted to true discoveries, this weekend gives observers and astrophotographers a unique chance to “mimic” a spurious discovery that has dotted astronomical lore: a visual “pseudo-moon” for the planet Mercury. This “moon illusion” will occur on February 8, 2013 during the closest conjunction of two naked eye planets in 2013. February offers a chance to see the fleeting Mercury in the sky, and this conjunction with Mars will provide the opportunity to see how Mercury would look in the night sky if it had a moon!

Mercury has been suspected of having moons before. On March 29th 1974, the Mariner 10 spacecraft became the first mission to image the innermost world up close. Mariner 10 mapped 40-45% of Mercury on 3 successive passes, revealing a pock-marked world not that different than our own Moon. But Mariner 10 also detected something more: brief anomalies in the ultra-violet spectrum suggestive of a moon with a 3 day period. For a very brief time, Mercury was thought to have a moon of its own, and NASA nearly made a press release to this effect. The spectroscopic binary 31 Crateris is now suspect in the anomalous readings. Still, the Mariner 10 observation made researchers realize the observations in the extreme UV were possible over interstellar distances.

The planet Mercury as seen by NASA's Messenger spacecraft (Credit: NASA/JPL).
The planet Mercury as seen by NASA's MESSENGER spacecraft (Credit: NASA/JHUAPL).

Today, NASA has a permanent emissary orbiting Mercury with its MESSENGER spacecraft. MESSENGER first entered orbit around Mercury on March 18th, 2011 after a series of trajectory changing flybys. MESSENGER has filled in the map of the remainder of Mercury’s surface, with no signs of the anomalous “moon.” Interestingly, MESSENGER was also on the lookout for “Vulcanoids” (tiny asteroids interior to Mercury’s orbit; sorry, Mr. Spock) while enroute to its final orbital insertion. NASA even released an April Fool’s Day prank of a fake “discovery” of a Mercurial moon dubbed Caduceus in 2012.

But MESSENGER has made some fascinating true to life discoveries, such as sampling Mercury’s tenuous exosphere & the possibility of ice at its permanently shadowed poles. Lots of new features have been mapped and named on Mercury, following the convention of naming features after famous deceased artists, musicians and authors set forth by the International Astronomical Union. It’s amazing to think that we had no detailed views at the entire surface of Mercury until the 1970’s, although some ground-based professional observatories and even skilled amateurs are now doing just that.

Fast forward to this weekend. Mercury is just beginning its first apparition of six in 2013 this week and is currently visible low in the dusk sky after sunset to the west. Mercury reaches greatest eastern elongation on February 16th at 18.1° from the Sun. Interestingly, that’s very close to the shortest elongation that can occur. Mercury’s orbit is eccentric enough that greatest elongation as seen from the Earth can vary from 17.9° to 27.8°. This month’s elongation happens within only 5 hours of Mercury reaching perihelion at 46 million kilometers from the Sun. This means that Mercury won’t peak above the dusk horizon for mid-northern latitude observers quite as high as it will during the next evening apparition of the planet in June.

Mercury Mars
caption =”Looking west 30 minutes after sunset on Feb. 8th from latitude 30° north.

 

This appearance of Mercury does, however, have some things going for it. First off, the ecliptic sits at a favorable viewing angle, roughly perpendicular to the western horizon at dusk for mid- to high northern latitude observers. This gives Mercury a bit of a “boost” out of the weeds. Secondly, Mercury is a full magnitude (2.512 times) brighter when it reaches maximum elongation near perihelion than aphelion, such as its next appearance in the dawn sky on March 31st of this year. Mercury will reach magnitude -0.5, versus +0.5 in late March.

To see Mercury, find a site with a western horizon free of ground clutter and start sweeping the horizon with binoculars about 15 minutes after local sunset. See a reddish dot just above Mercury? That’s the planet Mars, shining about 7 times fainter than -1.0 magnitude Mercury at magnitude +1.2. Mercury is fast approaching a conjunction with Mars; the two will be only 15’ apart (half the average width of a Full Moon) on the evening of February 8th at 17:00 Universal Time!

If you ever wondered how Mercury would appear with a moon, now is a good time to take a look! Again, binoculars are the best optical tool for the job. Can you see both with the naked eye? Can you place both in the same low power field of view with a telescope? You’ll only have a 15-30 minute window (depending on latitude) to snare the pairing before they follow the setting Sun below the horizon. Photographing the pair will be tricky, though not impossible, as they present a very low contrast against the bright background twilight sky.

Cass_Obs_13_Feb_5_6
caption =”Mercury (lower center) & Mars (upper center) imaged by Mike Weasner on February 5th.

 

Don’t expect to see detail on Mercury or Mars telescopically; Mercury only appears 5.8” across on the 8th, while Mars is 4” in apparent size. Mars disappears from view later this month to reach solar conjunction on April 18th 2013. The waxing crescent Moon just 1 day after New joins the pair on the evenings of February 10th and 11th.

Now for the “Wow” factor of what you’re seeing. The conjunction of Mars and Mercury only appears close; in reality, they are over 180 million kilometers apart. Mercury is 1.15 Astronomical Units (A.U.s)/178 million kilometers from us on February 8th, while Mars is nearly at its farthest from us at 2.31 A.U.s/358 million kilometers distant. It’s splendid to think that with Curiosity and friends operating on Mars and Messenger orbiting Mercury, we now have permanent robotic “eyes” on and around both!

Credits: Simulation created by the author using Starry Night.

Mercury & Mars courtesy of Mike Weasner and the Cassiopeia Observatory. Used with permission.