The May Moon Meets Venus and Mercury, at dusk en route to eclipse season and more.
Wonder where all the solar system action is hiding? While the dusk sky may seem devoid of planets (save for Mars), that’s all about to change this evening. The watch-phrase for astronomy in May 2021 is to ‘follow the Moon’ as it makes several spectacular planetary passes, then kicks off the first eclipse season of the year.
Incoming: The Earth-Moon system has company tonight.
The Asteroid: Near Earth Asteroid 2010 WC9 is back. Discovered by the Catalina Sky Survey outside Tucson, Arizona on November 30th, 2010, this asteroid was lost after a brief 10 day observation window and was not recovered until just earlier this month. About 71 meters in size, 2010 WC9 is one of the largest asteroids to pass us closer than the Earth-Moon distance.
2010 WC9 poses no threat to the Earth. About the size of the Statue of Liberty from the ground level to her crown, the asteroid is over three times bigger than the one that exploded over Chelyabinsk, Russia on the morning of February 15th, 2013.
The Pass: 2010 WC9 passes just 0.5 times the Earth-Moon distance (126,500 miles or 203,500 kilometers) on Tuesday, May 15th at 22:05 UT/6:05 PM EDT. That’s only roughly five times the distance of satellites in geosynchronous orbit. The asteroid is also a relative fast mover, whizzing by at over 12 kilometers per second. An Apollo-type asteroid, 2010 WC9 orbits the Sun once every 409 days, ranging from a perihelion of 0.78 astronomical units (AU) outside the orbit of Venus out to 1.38 AU, just inside the orbit of Mars. This is the closest passage of the asteroid by the Earth for this century.
Observing: This one grabbed our attention when it cropped up on the Space Weather page for close asteroid passes this past weekend: a large, fast mover passing close to the Earth is a true rarity. At closest approach, 2010 WC9 will be moving at 0.22 degrees (that’s 13 arcminutes, about half the span of a Full Moon) per minute through the constellation Pavo the Peacock shining at magnitude +10, making it a good telescopic object for observers based in South Africa as it heads over the South Pole.
North American and European observers get their best look at the asteroid tonight into early tomorrow morning while it’s still twice the distance of the Moon, shining at 13th magnitude and moving southward through the constellation Ophiuchus and across the ecliptic plane.
The best strategy to ambush the space rock is to simply aim a low power field of view at the right coordinates at the right time (see below), and watch. You should be able to see the asteroid moving slowly against the starry background, in real time.
Keep in mind, the charts we made here are geocentric, assuming you’re observing from the center of the Earth. Parallax comes into play on a close asteroid pass, and the Earth’s gravity will deflect 2010 WC9’s orbit considerably. Your best bet for generating a refined track for the asteroid is to use NASA JPL’s Horizons web interface to generate Right Ascension/Declination coordinates for the 2010 WC9 for your location.
How do you ‘lose an asteroid?” Often, an initial observation arc for a distant asteroid is too short to pin down a refined orbit. We have a blind spot sunward, for example, and fast moving asteroids can also be difficult to track across rich star fields and movement from one celestial hemisphere to the next. Recovery of 2010 WC9 earlier this month now gives us a solid seven year observation arc to peg its orbit down to a high accuracy.
Clouded out, or live in the wrong hemisphere? Slooh will carry an observing session for 2010 WC9 starting tonight at 24:00 UT/ 8:00 PM EDT. The Northholt Branch Observatories in London, England will also stream the pass live via Facebook tonight. Check their page for a start time.
There’s no word yet if Arecibo radar plans to ping 2010 WC9 over the coming days, but if they do, so expect to see an animation soon.
Don’t miss tonight’s passage of 2010 WC9 near the Earth, either in person or online.
47 Tucanae… the Coal Sack… Magellanic Clouds large and small… sure, it can be argued that the southern hemisphere sky has got all the “good stuff.” We’ve journeyed below the equator half a dozen times ourselves and we always make it a point to carry our trusty Canon 15x 45 image stabilized binocs – or track someone down with a serious ‘scope – even when astronomy isn’t the main focus of our particular away mission.
But did you know that you can glimpse one of the jewels of the southern hemisphere sky from mid-northern latitudes in May and June?
We’re talking about Omega Centauri in the constellation Centaurus. At a declination of -47 degrees south, it clears 5 degrees above the horizon as seen from around 37 degrees north, which corresponds to the latitudes of Richmond Virginia, Wichita Kansas and Sacramento, California in the United States and Seville Spain, Adana Turkey and Seoul South Korea worldwide.
In fact, it would be a fun project to see just how far north you could spot Omega Centauri from… located at right ascension 13 hours 26 minutes and declination -47 29’, Omega Centauri would theoretically juuusst clear the southern horizon at 52 degrees north, well into Canada… but has anyone caught sight of it that far north?
There’s evidence that Ptolemy knew of and recorded Omega Centauri in his Almagest as far back as 150 A.D. It was erroneously misidentified as a star over the centuries, hence the “Omega” designation. It was also too low in the southern sky to be included Charles Messier’s Paris-based catalog of deep sky objects, though it would’ve easily have made the cut had it been located farther north. Omega Centauri was first described by Edmond Halley in 1677 and made its catalog debut in 1746 when astronomer Jean-Philippe de Cheseaux listed it along with 21 other southern sky nebulae.
Shining at magnitude +4, Omega Centauri actually covers a section of sky slightly larger than the apparent size of a Full Moon and is an easy naked eye object from the southern hemisphere. From south of the equator we can easily pick out Omega Centauri from a dark sky site. On a recent trip to the Florida Keys, we could easily detect Omega Centauri riding high to the south over the Straits of Florida at local midnight. In fact, Arthur Upgreen muses in his fantastic book Many Skies just what Florida skies would look like if Omega Centauri were much closer to Earth, filling up the southern horizon scene.
Now for the wow factor of what you’re seeing. The largest of the 150-odd known globular clusters associated with our Milky Way Galaxy, Omega Centauri is almost 16,000 light years distant and weighs in at an estimated 4 million solar masses. Globular clusters are ancient structures and Omega Centauri contains millions of Population II stars dating from an age of about 12 billion years ago. The density at the core of the cluster is equal to a star per every 1/10th of a light year apart, and any planets orbiting said stars would host truly dazzling skies.
The bright star Spica (Alpha Virginis) in the constellation of Virgo the Virgin makes a good guide to find Omega Centauri from the northern hemisphere, as both have nearly the same right ascension to within 10 arc minutes of each other. Both currently transit the southern meridian at around 11:00 AM local in late May, and Omega Centauri lies just 35 degrees — about 3 ½ hand widths held at arm’s length — south of Spica.
And speaking of Centaurus, the constellation was also recently host to a naked eye nova last year as well. Nova Cen 2013 topped out at magnitude +3.3, though it was placed much farther south than Omega Centauri.
Another unique target in the constellation Centaurus is known as Przybylski’s Star. A seemingly nondescript +8th magnitude star, Przybylski’s Star has some peculiar spectral properties of rare trace elements. It also sits near the same declination as Omega Centauri at -46 43’ and has a right ascension of 11 hours 38’.
Finally, there’s another southern hemisphere treat peeking just above the southern horizon on late May and June evenings… look about 13 degrees to the lower right of Omega Centauri at around 10:30 PM local in late May, and you might just spy Gacrux (Gamma Crucis), the +1.6 magnitude star that makes up the “head” of the constellation Crux, the Southern Cross. This tough to spot target just tops out at 5 degrees above the southern horizon from here in Tampa Bay, Florida, beckoning northern hemisphere observers on these sultry May and June evenings to the jewels that lie just beyond the horizon to the south.
An often ignored meteor shower may offer fine prospects for viewing this weekend.
The Eta Aquarid meteors provide a dependable display in early May. With a radiant very near a Y-shaped asterism in northern Aquarius, the Eta Aquarids are one of the very few major showers that provide a decent annual show for southern hemisphere residents.
This year, the peak of the Eta Aquarids as per the International Meteor Organization (IMO) comes on May 6th at 1:00 UT, or 9:00 PM EDT on May 5th. This favors European longitudes eastward on the morning of Monday, May 6th. The Eta Aquarid radiant rises just a few hours before dawn, providing optimal viewing in the same time frame.
Keep in mind, the shower is active from April 19th to May 28th. Predicting the arrival of the peak of a meteor shower can be an inexact science. North American observers may still see an early arrival of the Eta Aquarids on May 5th or even the morning of the 4th.
Could “the 4th be with us” at least in terms of meteor shower activity?
The Eta Aquarids are one of two annual meteor showers associated with that most famous of comets: 1P/Halley. The other shower associated with Halley’s Comet is the October Orionids. This makes it one of the very few periodic comets associated with two established annual meteor showers.
Like the Orionids, the Eta Aquarid meteors have one of the highest atmospheric velocities of any shower, at 66 kilometres per second. Expect short, swift meteors radiating from low in the southeast (or northeast if you’re based south of the equator) a few hours before local dawn.
This year’s ZHR is expected to reach 55. This year also offers outstanding prospects, because the Moon is only a 17% illuminated waning crescent just 4 days from New at the shower’s peak. There’s some thought in the meteor observing community that this shower experiences a cyclical peak every 12 years.
If this is indeed the case, we could be headed towards a mild lull in this shower around the 2014 to 2016 time frame. Performances from the Eta Aquarids over the past few years as per data from the IMO seem to bear this out, with a peak around 2009;
Still, 55 per hour is a respectable shower. Keep in mind, the ZHR stands for the “Zenithal Hourly Rate” and is an ideal number. This is the number of meteors an observer could expect to see under dark skies with no light pollution with the radiant directly overhead. Also, remember that no single observer can monitor the entire sky at once!
This is also one of the last big annual showers of the season until the Perseids in mid-August. The Gamma Delphinids (June 11th) and the June Bootids (Jun 27th and the June Lyrids (June 15th) are the only minor showers in June. July also sees another minor shower radiating from the constellation Aquarius, the Delta Aquarids which peak on July 30th. The daytime Arietids in June would put on a fine annual showing if they didn’t occur in… you guessed it… the daytime.
This weekend’s Eta Aquarids will put on a better display for the southern hemisphere, one of the very few showers for which this is true.
It’s a poorly understood mystery. Why does the northern celestial hemisphere seem to contain a majority of major meteor shower radiants? The Geminids, the Leonids, the Perseids, the Quadrantids… all of these showers approach the Earth from above the celestial equator, and even from above the ecliptic plane. The Eta Aquarids are one of the very few major showers that goes against this trend.
Is it all just a coincidence? Perhaps. Like total solar eclipses, meteor showers are as much a product of our position in time as well as space. New streams are shed as comets visit the inner solar system, some for the very first time. These older trails interact with and are dispersed by subsequent passages near planets. The 12 year fluctuation of the Eta Aquarids is thought to be related to the orbit of Jupiter which has a similar period.
For example, one meteor shower known as the Andromedids was prone to epic storm outbursts until the early 20th century. Now the stream is a mere trickle. Meteor showers evolve over time, and perhaps their seeming affinity for the northern hemisphere of our planet is a mere perception of our epoch. Maybe a future study could discern a bias due to the number of prograde versus retrograde cometary orbits, or perhaps statistical scrutiny could reveal that no such partiality actually exists.
All food for thought as you keep vigil these early May mornings for the meteoric “Drops from the Water Jar…” Be sure to post those meteor pics to the Universe Today’s Flickr forum, report those meteor counts to the International Meteor Organization, and tweet those fireball sightings to #Meteorwatch!