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Bruce BettsDecember 13, 2018

Go Out and See the Geminid Meteor Shower

The Geminid meteor shower peaks tonight, 13/14 December.  The Geminids are usually the best meteor shower of the year, producing 100 or more meteors per hour seen from a dark site. So take some time to go out and stare at the sky. 

Geminid Meteor

Bruce Betts

Geminid Meteor
Example of a meteor streaking across the sky, in this case a Geminid meteor from December 2013 passing close by Polaris (the North Star).

Meteors and Meteor Showers

Meteors are streaks of light in the sky caused by space stuff (a technical term) burning up as it hits the upper atmosphere of the Earth at very high speeds (tens of kilometers per second).  That space stuff usually consists of small dust and sand-sized dirt and rocks.  Even these small things can cause streaks of light you can see from the ground at night.  As an approximation, the bigger the dirt that hits, the brighter the light. 

Any night of the year, if you watch the sky from a dark site, you may see 10 or so meteors per hour.  But there are meteor showers at certain times of year that make it much more likely you’ll see a meteor.  Meteor showers occur when the Earth passes through the debris shed by a comet sometime in the past.  The next year, Earth will pass through the debris orbit again on about the same date. 

Two of the best meteor showers of the year are the Perseids, which peak around 12 or 13 August and the Geminids, that peak near 13/14 December.  The Perseids often get more press because they occur during the warmer (for the Northern Hemisphere) Summer.  But, the Geminids typically produce more meteors. 

Meteor showers are named after the constellation that contains the radiant of the shower. The radiant is where the meteors appear to emanate from: if you draw a line back along the meteors, all of the lines will meet at a point. So, Geminid meteors all seem to come from a point in the constellation Gemini. The radiant is an effect of us (Earth) moving through the debris.  The debris hits in parallel lines, but perspective causes us to see the meteors as all seeming to originate from the radiant.  

Watching Meteor Showers

All you need to watch meteors are your eyes, no clouds, and patience.  Go out, get comfortable and stare at the sky.  Typically the best time to see a meteor shower is between midnight and pre-dawn because that is when you are on the leading side of the Earth, so the side of Earth slamming into debris rather than the debris having to catch up to the Earth (like more rain hitting your front windshield than you back when driving).  Details of best meteor shower observing depend on moonlight and the timing and placement of the radiant in the sky. 

You don’t have to stare in the direction of the radiant, in fact meteors will appear longer away from the radiant.  Ideal is often said to be 45 degrees away from the radiant, but probably more important is to find the darkest place you can, don’t have a light in your eyes (in fact, let your eyes adjust to the dark for many minutes), and look at the darkest patch of sky you can.

The 2018 Geminid Meteor Shower

The 2018 Geminids peak on the night of 13 December through the morning of the 14th.  Unlike other comet-produced meteor showers, the Geminids are caused by debris from strange asteroid called 3200 Phaethon.  It may be a former comet, and is sometimes referred to as a rock comet.  But in any case, it sheds material when it comes close, very close, to the Sun in its 524-day orbit.  Random Space Fact: Phaethon’s orbit brings it closer to the Sun than any other named asteroid, with a perihelion of 20.9 million km, less than half of Mercury’s closest point to the Sun.

On the night of the 2018 Geminids peak, the Moon is nearing first quarter and sets around 22:30 local time.  Visibility will be better after that, but you can observe sooner; just try to preserve your night vision by keeping your back to the Moon.  Though meteors will be visible all night, the peak will likely fall around 0200 local time when the radiant is high overhead.  One advantage of evening viewing is though you will see fewer meteors, you may see some Earthgrazers – long meteors burning up very high in the atmosphere.  Later meteors hit more head on and appear shorter.

Note that though peak meteor counts from a dark side can be over 100 per hour, light pollution will cut that number drastically.  If you can’t head to a dark site, try looking in the darkest part of your sky and you will likely still be rewarded with some meteors, particularly if you are patient.  But what if it is cloudy on the peak night?  Try the next night. There will be fewer meteors, but still far more than normal.

Go out, look up at the night sky and have fun!

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Bruce Betts

Chief Scientist / LightSail Program Manager for The Planetary Society
Read more articles by Bruce Betts

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