Coming Attraction: Geminid Meteor Shower 2011

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It’s the finale of this year’s meteor showers: The Geminids will start appearing on Dec. 7 and should reach peak activity around the 13th and 14th. This shower could put on a display of up to 100+ meteors (shooting stars) per hour under good viewing conditions.

However, conditions this year are not ideal with the presence of a waning gibbous Moon (which will be up from mid-evening until morning). But seeing meteors every few minutes is quite possible. Geminid meteors are often slow and bright with persistent coloured trails which can linger for a while after the meteor has burned up.

There is something unusual about the Geminid meteor shower, as normally meteor showers are caused by the Earth ploughing through the debris streams created by comets and their tails. But the object that created the specific stream of debris associated with the Geminids is not a dusty icy comet, but a rocky asteroid called Phaethon 3200.

Phaethon 3200 belongs to a group of asteroids whose orbit cross the Earth’s. It turns out to be an unusual member of that group: Not only does it pass closer to the Sun than the others but it also has a different colour, suggesting a different composition to most asteroids.

Credit: Adrian West

One of the curious things about the Geminid particles is that they are more solid than meteoroids known to come from comets. This is good for meteor watchers; giving us brighter meteors.

Observations by astronomers over decades have shown that meteor rates have increased as we reach denser parts of the stream.

It is not known exactly when the asteroid was deflected into its current orbit, but if it was originally a comet it would have taken a long time for all the ices to have been lost. However, it is possible that it may have been a stony asteroid with pockets of ice.

We are unsure of the origins and appearance of Phaethon 3200, but its orbit has left us with a unique legacy every December, with little steaks of light known as the Geminid meteor shower.

You will only need your eyes to watch the meteor shower, you do not need telescopes binoculars etc, but you will need to be patient and comfortable. See this handy guide on how to observe meteors

During a meteor shower, meteors originate from a point in the sky called the radiant and this gives rise to the showers name e.g. The Geminids radiant is in Gemini, Perseids radiant is in Perseus etc.

Don’t be mislead by thinking you have to look in a particular part of or direction of the sky, as meteors will appear anywhere and will do so at random. You will notice that if you trace back their path or trajectory it will bring you to the meteor showers radiant. The exception to this rule is when you see a sporadic or rogue meteor.

Tell your friends, tell your familly and tell everyone to look up and join in with the Geminid meteorwatch on the 12th to the 14th December 2011. Use the #meteorwatch hashtag on twitter and visit meteorwatch.org for tips and guides on how to see and enjoy the Geminids and other meteor showers.

Credit: Wally Pacholka

Does a “Rock Comet” Generate the Geminids?

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Many annual meteor showers have parent bodies identified. For example, the Perseids are ejecta from the comet, Swift-Tuttle and the Leonids from Tempel-Tuttle. Most known parent bodies are active comets, but one exception is the Geminid meteor shower that peaks in mid December. The parent for this shower is 3200 Phaethon. Observations of this object have shown it to be largely inactive pegging it as either a dead comet or an asteroid. But on June 20, 2009, shortly after perihelion, 3200 Phaethon brightened by over two magnitudes indicating this object may not be as dead as previously considered. A new paper considers the causes of the brightening and concludes that it could be a new mechanism leading to what the authors deem a “rock comet”.

David Jewett and Jing Li of UCLA, the authors of this new paper, consider several potential causes. Due to the size of 3200 Phaethon, they suggest that a collision is unlikely. One clue to the reason for the sudden change in brightness was a close link of a half of a day to a brightening in the solar corona. Given a typical solar wind speed and the distance of 3200 Phaethon at the time, this would put the Geminid parent just at the right range to be feeling the effects of the increase. However, the authors conclude that this cannot be directly responsible by imparting sufficient energy on the surface of the object to cause it to fluoresce due to an insufficient solar wind flux at that distance.

Instead, Jewett and Li consider more indirect explanations. Due to the temperature at 3200 Phaethon’s perihelion (0.14 AU) the presence of ices and other volatile gasses frozen solid and then blasting away as often happens in comets was ruled out as they would have been depleted on earlier orbits. However, the blow from the increased solar wind may have been sufficient to blow off loosely bound dust particles. While this is plausible, the authors note that the amount of mass lost if this were the case would be a paltry 2.5 x 108 kg. While it’s possible that this may have been the cause of this single brightening, this amount of mass loss to the overall stream of particles responsible for the Geminid shower would be insufficient to sustain the stream and similar losses would have to occur ~10 times per orbit of the body. Since this has not been observed, it is unlikely that this event was tied to the production of the meteors. Additionally, it is somewhat unlikely that it could even be the event for this sole case since repeated perihelions would slowly deplete the reservoir of available dust until the body was left with only a bare surface. Unlike active comets which continually free dust to be ejected through sublimation of ice, 3200 Phaethon has no such process. Or does it?

The novel proposition is that this object may have an unusual mechanism by which to continually generate and liberate dust particles of the size of the Geminids. The authors propose that the heating at perihelion causes portions of the rock to decompose. This process is greatly enhanced if the rock has water molecules bonded to it and lab experiments have shown that this can lead to violent fracturing. Such processes, if present, could easily lead to the production of new dust particles that would be liberated during close approach to the sun. This would make this object a “rock comet” in which the properties of a comet’s dust ejection via gasses would be carried out by rocks.

To confirm this hypothesis, future observations would be needed to search for subsequent brightening at perihelion. Similarly, it should be expected that such a process may make a faint cometary tail with only a dust component that may be visible as well, although the lack of any such detection so far, despite studies looking for cometary tails, casts some doubt on this process.

Join the World in Looking for Geminids This Weekend with #MeteorWatch

Amateur astronomers around the world will be watching for what is predicted to be one of the year’s best meteor showers, the Geminids. Join in and make it a global experience with another #Meteorwatch on Twitter. #Meteorwatch, which occurred during the Perseid meteor shower in mid-August, is a social media astronomical event that was a big hit among Twitterers. But there’s lots of ways to join in, not only on Twitter. Everyone is welcome whether they are an astronomer or just have an interest in the night sky. The aim is to get as many people to look up as possible and maybe see meteors or even some fireballs for the first time.
Continue reading “Join the World in Looking for Geminids This Weekend with #MeteorWatch”

Tips for Viewing the Geminid Meteor Shower

Occurring every year in mid-December, the Geminid meteor shower is commonly referred to as the most reliable meteor shower of the year. That is, it almost always puts on a great show!

The Geminid meteor shower is sure to be a stunning show this year, as the Moon will not be visible at night, so its glow will not impede your meteor viewing ability. In addition, the Geminids’ radiant is favorably positioned for most viewers at this time of year. In order to see the most meteors, I suggest the following tips:

  • The Geminid meteor shower has a very broad maximum peak. Because of this, the night on which you view the meteors isn’t critical. You will of course, see more meteors on the peak nights. This year the Geminid meteor shower’s peak is the night of December 13th-14th, 2009.
  • The best time to view a meteor shower is in the late night to early morning hours. The best time to view a meteor shower typically begins around 2 AM. This is because as the Earth rotates toward dawn, the forward velocity of the planet adds to the linear velocity of the surface and atmosphere. This has the effect of “sweeping up” more meteors.
  • If you’re not normally awake at 2 AM, like many people, simply go to sleep very early and set an alarm clock to wake you up to view the meteor shower. Trust me on this point, it is definitely worth it.
  • The Geminid meteor shower’s radiant is right near the twin bright stars Castor and Pollux in Gemini. Click the image at top right to see a map (thanks to Stellarium). The trick, however, isn’t to look towards the radiant, but to keep your eyes on the whole sky. While it’s impossible to look at the whole sky, just keep your eyes scanning and alert. This increases your chances of seeing a fleeting meteor or one out of the corner of your eye.
  • Darkness is key to proper meteor shower viewing. If you live in a city or other light polluted area, try going to a dark sky site to truly experience a meteor shower. You might be surprised how close a dark sky site is to you! Here are some tips on finding a dark sky near you.
  • Dress warm! The cold December air will seem extra cold, since you’ll be sitting outside, inactive for the most part. I also have some tips on cold-weather astronomy at Visual Astronomy. If you are too cold, go inside for a bit! Your safety is not worth seeing some meteors!
  • Keep comfortable, too! I’ve found the best way to watch meteor showers is either laying down in a sleeping bag, or on an Adirondack or other reclining lawn chair. This allows you to keep your eyes on the sky without straining your neck!
  • Keep safe! If you’re traveling to an unknown or unfamiliar area to watch the meteor shower, don’t travel alone! Take a buddy with you. Not only is this great for safety, but meteor showers should be a social event, and are fun to share with a friend!
  • Green lasers are great for pointing out celestial objects. I use one to point out objects to people, and it works much better than trying to point with your hand. Just be careful with it and do not use a laser more powerful than 5 mW.
  • Finally, if you’re feeling ambitious, take pictures! This is a real challenge, but if you’re up to it, it’s a very rewarding challenge. You’ll need a tripod and a camera that can take long exposures. Set your exposure for somewhere around 30 seconds and let it record the whole sky. If a meteor crosses the field of view, it will be captured, and you can keep it forever!

So using these tips, you can get the most out of your Geminid viewing experience!