2011 Perseid+Jupiter Credit: David Dickinsen
Sure, you’ve heard of the August Perseids that come blazing across the sky and are invariably trumpeted by the news as the “Meteor Shower of the Millennium!” on a yearly basis. Perhaps you’ve even heard of the Leonids, normally a feeble November shower prone to legendary outbursts roughly every 33 years. But have you ever heard of the October Draconids?
I’ll admit I hadn’t until the October 1998 issue of Sky & Telescope arrived on my doorstep. Or should I say tent-flap? You see, the last half of 1998 found me deployed with my U.S. Air Force squadron to Al Jaber, Kuwait. In those days, email (and spam) were still a hip “new thing,” giant washing-machine-like CRT monitors adorned many office desks, and we were involved with a cat-and-mouse game between Saddam and the U.N. Inspectors that eventually became the shooting war of Operation Desert Fox. A military base in the desert was also a fine place to do some causal astronomy. The Leonids put on a fine show that year approaching storm levels of 1,000 per hour from our longitude. I remember mentioning the Leonid meteors to one of our F-16 pilots, and they later briefed not to mistake the fireball flashes for Iraqi AAA (an important distinction!)
But the Draconids are a shower of a different breed. The progeny of Comet 21P/Giacobini-Ziner (Call the meteor shower by the even more obscure name of the Giacobinids if you want to be really cool/nerdy/pedantic) a short period comet in a 6.6 year orbit, this shower can be notoriously unpredictable and prone to short, quick out-bursts. Discovered on December 20th, 1900 by Michel Zinner, the comet was again recovered by Ernest Zinner two passages later on October 23rd 1913 from the Remeis Observatory in Hamburg Germany (hence the hyphenated name) and was 1st recognized as a potential source of Earth-intersecting meteors in 1915 by M. Davidson. In fact, Davidson correctly predicted a 1926 outburst that generated a zenithal Hourly Rate (ZHR) of about 17, and the hunt was on. The Draconids/Giacobinids really put on a memorable display in 1933 with a ZHR of 3,000-29,000 meteors (!) the same year as the historic Leonid outburst and one of the greatest meteor storms of the twentieth century. While the term “meteor storm” is a somewhat informal term, its generally applied to a shower with an observed rate of about 1,000 per hour. Lots can conspire to lower this ideal rate, such as terrestrial light pollution, the Moon (more on this in a minute), the fact that a sole observer can’t cover the entire sky, the fact that most of us don’t have the radiant directly overhead, the need to take breaks… well, you get the idea. Everything seems to conspire to get between you and your meteor watching experience. A shower with a ZHR of 100 is a pretty good show; you’ll maybe see a couple every 10 minutes. A ZHR of 10 is our cutoff for a “think about setting my alarm for 2AM” shower, and the general sporadic rate for the northern hemisphere hovers around a ZHR of 5 for a good part of the year. (It’s rumored that the astro-gods decreed that the northern hemisphere should get all the good meteor showers, while the southern gets all the good deep sky objects!) A ZHR of +1,000 means a meteor every several seconds, possibly several at once! In fact, observers of such showers have reported the “driving in a snow-storm effect” as the Earth plows through the meteor stream, a very retro-Star Trek illusion.
Draconids Credit: David Dickinsen
Since that landmark 1933 outburst put the Draconids on the map, their 6.6 year return has been fickle, to say the least. They were almost non-existent in 1939, only to dazzle again with a ZHR of 3,000 to 6,000 per hour in 1946. The shower is obscure enough that I would bet many historical outbursts have simply gone unreported, and it’s very probable that pre-discovery mentions of the obscure October shower are waiting to come to light. The shower went into a lull until 1985, when a ZHR of about 600-800 was observed, many by radar.
And the 1998 shower? Well, a respectable short quick outburst was indeed noted by Far East observers; a team led by Takema Hashimoto in Japan estimated rates approaching 500 per hour, as did several other teams. However, the Beijing Observatory to the west with a limiting magnitude of about +4 recorded a paltry 50-75 per hour, and by the time Europe turned into the stream the ZHR had already fell below 10. Clearly, any associated streams of meteoritic material associated with the Draconids are dense but compact and our interaction with it tends to be short-lived. The 1998 Draconids were also a bust from my Middle Eastern location, although the Leonids a little more than a month later more than made up for them. Likewise, the 2004 Draconids where a bust, but it’s never stopped me from looking for them every 6 to 7 years in early October, a Moby Dick to my astro-Ahab…
So, what about 2011? Well, first the good news. The Earth will indeed thread a path between two meteor streams shed by Giacobini-Ziner; an 1873-94 stream and a 1900 stream. Meteoriticists Jeremie Vaubaillion and Mikiya Soto estimate that that we may be in for a ZHR of 60 around 17:09 Universal Time on October 8th (the 1873-94 stream), followed by a stronger outburst of 600+ per hour at 19:57UT (the 1900 stream). This would strongly favor northern Europe, although anyone living in the northern hemisphere with clear skies is urged to watch 24 hours on either side of this prediction. The radiant of the Draconids lies at a northerly declination of +54° in the head of the constellation Draco, another bonus for northern observers. This means that unlike showers with radiants that have a more southern declination, there’s a chance to see meteor activity start to pick up slightly before midnite.
Now for the bad news… first off, the Moon reaches Full phase on October 11th, and thus will definitely play a role in diminishing the number of meteors observed. Also, the predicted area of northern Europe is statistically cloudy in early October, although they could be due for a reprieve. Lastly, no one knows how dense these pre-1900 streams are, as there’s no record of them! Also troubling is the fact that the hoped-for 1900 stream lies ahead and outside the stream path, an area that’s been historically a bust… the 1946, 1933, and 1985 outbursts were from areas behind and inside the stream.
Vaubaillion and the SETI Institute also plan to fly a Multi-Instrument Aircraft Campaign to observe the Draconids, a sure sign that folks in the know are taking the possibility of an outburst seriously. If Charlie Sheen and friends can stay out of the news for one weekend, there’s even a chance that news of the Draconids can be this month’s “storm of the century…”
But there’s one last reason that you should get out and watch for Draconids this weekend. In the October 2011 issue of Sky & Telescope, Peter Jenniskens of the SETI Institute notes that this may be the last predicted meteor storm until 2030…although when I look at the position of the projected 2018 Draconids sitting Sooooo close to the 1946 swarm, I wonder…
Finally, a curious note about the life span of this shower… professor K. Fox of Queen Mary College, England ran a simulation of the Draconid stream backward and forward suggesting that the current era of this shower started in 950 A.D., and by 2950 A.D., this shower will cease to occur! We can thank the planet Jupiter for shepherding comet 21P/Giacobini-Zinner into its current stunted orbit, and our current position in space and time allows us to observe this largely unknown and poorly understood shower.
So get out there, pour a favorite hot beverage of choice, and be sure to Tweet those sightings/musings to #meteorwatch… you just might see the storm of a lifetime. And be sure to remember the cardinal mantra of meteor observing; you won’t see any if you don’t try!
