Long exposure of the sky during the Geminids meteor shower in 2007. (Berkó Ernő)
The annual Geminids meteor shower will reach its peak of activity on the morning of Saturday, Dec. 14. Here's an opportunity to renew your childlike wonder and eagerness to catch a falling star.
What You’ll See
The best time for viewing is around 2 a.m., when the shower’s “radiant point” — the spot in the sky from where the meteors appear to emanate — is almost directly overhead.
The cold, often crystal-clear late Autumn morning skies can offer a good, dark backdrop to the fleeting streaks of meteors. Normally, you might spot up to 50 meteors an hour at the Geminids’ peak of activity.
This year, the waning Gibbous moon will be in the sky during prime meteor-watching time, so its light may drown out some of the fainter meteors. At 2 a.m., the moon will be positioned almost directly at the Geminids’ radiant point in the constellation Gemini, this shower’s namesake.
The moon won’t completely spoil the show, though; meteors can appear anywhere in the sky. Besides, the moon is beautiful to look at while you wait for the next meteor to streak by.
Where to See It
The best viewing location is a good, safe spot as far away as possible from large cities and the light pollution they produce. If the moon’s light can drown out the fainter meteors, so can the urban sky glow.
Around the Bay Area, good meteor-watching areas include Skyline Boulevard on the Peninsula, the Santa Cruz Mountains, and the more rural areas of Marin, Sonoma and Napa counties. Keep in mind that the closer you are to the ocean, the more vulnerable you are to foggy conditions.
In the East Bay, you could try viewing from Mount Diablo or the Sunol Regional Wilderness. Even though the gates to the parks close at sunset, you can pull over at spots along the roads that lead up to them.
In the South Bay, Henry Coe State Park is a stargazer’s favorite —and the gates stay open around the clock.
Be aware that the weather forecast as of Wednesday afternoon is calling for periods of light rain through Saturday. Dress warmly, bring hot beverages and something to sit or lie down on, and look up, taking in as much of the sky as you can. Then, wait. Meteors are fast. They vanish as quickly as they appear, and you never know where one will show up.
Occasionally an exceptionally bold and bright meteor will make an appearance. Depending on its composition and temperature, it may even look blue, orange or yellow. Seeing just one of these can make your early morning shower-viewing expedition worthwhile.
What is a Meteor Shower, and What Causes the Geminids?
A meteor is a tiny speck of rock or metal that burns up in Earth’s atmosphere, leaving behind a luminous trail of vaporized material that quickly cools and fades from view.
A meteor shower occurs when the Earth passes through a cloud of dust in space, typically left behind by a comet orbiting the sun. When the comet, composed mostly of ice, a sprinkling of dust, and maybe some rocky chunks passes close to the sun, it heats up, and some of the ice is vaporized. An eruption of gas and dust occurs, producing the comet’s familiar tail and leaving behind a trail of debris — mostly specks of rock and metal no bigger than your fingernail.
Earth moves along its orbit at a speed of 18 miles per second. When combined with the dust trail’s orbital motion, the collision between dust particles and the atmosphere is intense. Friction quickly superheats the tiny speck, and in a flash it’s history.
People generally see meteor showers only in the morning hours, because the morning skies face the direction Earth is moving through space. If that’s difficult to visualize, think about this: When a car speeding along the freeway plows through a swarm of flying insects, you only see bug streaks appear on the windshield.
Rock Comets Versus Regular Comets
While most meteor showers are caused by the dusty debris left behind by comets, the Geminids shower is different in that the object that produces its dust trail is not exactly a comet.
3200 Phaeton, the Geminids’ parent object, is a class of asteroid often called a “rock comet.” Orbiting the sun every 1.434 years, 3200 Phaeton passes within 13 million miles of the sun at its closest approach, about one-third the distance of Mercury from the sun.
Like a comet, and unlike a typical asteroid that is composed mostly of rock and metal, 3200 Phaeton exudes a trail of dust after an encounter with the sun heats it up.
Whether the dust is blown into space by the vaporization of volatile ice on or within this object; from the fracturing of rock caused by thermal expansion; or from a combination of both, the result is that 3200 Phaeton leaves a stream of dust in its wake that Earth plows through every December.
Meteor Showers Are Worth the Effort to See Them
Don’t let the cold, dark, sleepy morning hours scare you away from experiencing a light show like the Geminids meteor shower. It may take some planning, careful selection of clothing, dusting off the folding chairs you keep in the basement, and a bit of driving, but once you set up camp and see that first fiery spark dash through the sky, you’ll be glad you did it.
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