ELI ON EARTH: Geminids Come to East Lansing

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Monday, December 8, 2014, 12:23 am
Aron Sousa

Image of Geminid meteor courtesy of NASA

The 2014 viewing of the Geminids meteor shower will come to East Lansing this week, peaking on the night of Saturday, December 13. These meteor showers are usually best seen at 2-3 am in a dark area away from city lights. But on the peak night of December 13-14 this year, the waning half moon will rise around midnight, and after that point its light will compete with the meteor showers. So East Lansing residents will probably have better meteor viewing—and be better rested on Sunday—if they try to see the Geminids before the midnight appearance of the moon. (Those walking to and from the High School Collage Concert on Saturday night might look for meteors along the way.)

The meteors will be visible throughout the sky, and there will likely be 100 meteors per hour at the peak time. Watching a meteor shower is not complicated, but here are a few tips:

  • Get away from light pollution. Streetlights and other sources of light pollution may wash out the light from the meteors.
  • Watch for at least 20 minutes. Our eyes need to accommodate to the darkness and recharge the light-sensing proteins rhodopsin and retinal in the night vision rod cells of the retina. You can preserve your night vision by limiting use of artificial light to red light, which causes minimal depletion of rhodopsin in the retina, or by covering one eye with an eye patch and uncovering and using the patched eye when you want to see in the dark. (Disclosure: you will look like a pirate.)
  • Do not bother with binoculars or a telescope when viewing meteors; your eyes have a wider field of vision and survey a larger patch of the sky than telescopes or binoculars can.
  • Dress warmly, look at the sky, and have a little patience.

The Geminids get their name from the astronomical constellation Gemini, which rises in the east around sunset and is overhead at about midnight this time of year. Although the meteors may be visible anywhere in the sky, the path of movement of the meteors will trace back to the area of the Gemini constellation.

Meteors are bits of dust and rock that heat up and burn as they enter the earth’s upper atmosphere at speeds of more than 20,000 mph. Most meteors are thought to come from the debris that sprays off of comets as they heat up when passing the sun. When the earth passes through the debris stream of the comet, the debris hits the earth’s atmosphere, heats up, glows, and so becomes what we call meteors.

The Geminids come from the debris coming off of the asteroid 3200 Phaethon, an asteroid which orbits the sun every year and a half and passes closer to the sun than the planet Mercury before heading back out beyond Mars’s orbit. The Geminids are the only meteor shower linked to an asteroid rather than a comet. (Comets give off junk that produce a bright, visible tail, and asteroids do not.)

The quandary posed by the Geminids is that asteroids like 3200 Phaethon do not spray debris as they orbit the sun, so, how could the stuff that causes meteors be coming off this asteroid and becoming meteors? It may be that 3200 Phaethon, which orbits close to the sun frequently, may have long ago boiled off all of its water and other volatile components leaving a debris stream that the earth now passes through each December. If this is the case, 3200 Phaethon is a burned-out comet, and the debris from its days as a comet are still orbiting the sun.

While some meteor showers have been recorded for thousands of years, the Geminids were first noticed and written about in the middle of the 1800s. It appears that the orbit of the earth and the orbit of 3200 Phaethon’s debris did not cross paths until then. The Geminids have been intensifying since they were first seen and will continue to intensify for several more decades before beginning to wane.

The author is hoping for clear skies on Saturday, and will be walking to and from the Collage Concert.


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