Your calendar-challenged weather blogger has an apology to make. In Sunday's Maryland Weather blog post, I listed Tuesday night/Wednesday morning as the peak of the annual Geminid meteor shower.
The actual peak, it's finally dawned on me, is Monday night/Tuesday morning. My bad. I read "midnight Tuesday" in my astronomical calendar as the hour when Tuesday ends, not the one where it begins.
Anyway. I'm owning up to my error now so that anyone hardy enough to brave the bitter cold tonight can get out there in time to see the Geminid shower at its best.
That is, of course, assuming the skies clear in time. Tuesday/Wednesday actually promises better seeing conditions for Central Maryland. And meteor counts will still be pretty high, although not at Monday/Tuesday morning's peak. Rhiannon Blaauw, at NASA's Meteoroid Environment Office, in Huntsville, Ala., said meteor rates Tuesday/Wednesday night should be 30 to 50 an hour between 1 a.m. and 3 a,n, under dark skies.
Here's more on the event, below. Again, my apologies.
The Geminids at their peak can generate more than 80 meteors an hour or more for observers who can get away from the light pollution of the urban corridor.
And they have a great story to tell.
Astronomers have linked the annual Geminid shower to one of the solar system's oddballs – an object discovered in 1983 and named 3200 Phaethon. It was ther first time since the Geminid shower - the year's most intense shower - was first described in the 1800s that anyone had identified their source.
Phaethon's orbit made it seem to be an asteroid — a three-mile-wide chunk of rocky debris from the construction of the solar system 4.5 billion years ago. It appears to have emerged from the main asteroid belt, between the orbits of Mars and Jupiter, scientists said. Its color matched other asteroids, and it didn't show a comet's tail when it approached the inner solar system.
But even so, debris tossed off along Phaethon's path as it circles the sun seems to be responsible for the annual Geminid meteor shower. Rocky asteroids aren't supposed to do that.
Other meteor showers have been linked to icy comets — frozen snowballs from the outer reaches of the solar system that toss off gas and dust as they near the sun. Annual meteor showers occur as the Earth, on its own orbit around the sun, intersects and passes through that comet dust.
Even more curious, astronomers traced the debris in the Geminid stream back to Phaethon at a point in its orbit when it passed inside the orbit of Mercury - very close to the sun.
Scientists using NASA's STEREO spacecraft last year spotted Phaethon just 15 solar diameters from the sun. And while they watched, Phaethon brightened. Scientists at UCLA surmised that its surface rocks were being broken up by the sun's heat and radiation — a possible mechanism for creating the debris that causes the Geminid shower.
There are still problems with the hypothesis. Others argue Phaethon is a husk of a comet that lost all its ices during previous encounters with the sun.
This business of main belt asteroids that unexpectedly light up and toss off debris has become a "real hot topic," said Keith Noll, an astronomer at the Space Telescope Science Institute in Baltimore. "People have realized that there are objects that look like ordinary asteroids, yet they become active like comets, although at a low level."
Scientists would now like to know whether these objects are comets from far beyond the planets that got "implanted" in the asteroid belt, Noll said. "Or, have they always had this stuff underneath? And what does it take to turn them on?"
He said astronomers learned over the weekend about another object, called 596 Schelia, previously thought to have been an asteroid, that has had an "outburst," perhaps one like Phaethon's.
"This may be just part of a general process of these things that's going on all the time," Noll said.
Still other scientists will monitor the Geminids tonight as they impact the Earth's atmosphere and the moon. Using all-sky cameras and telescopes trained on the moon, they will try to quantify the meteors that manned spacecraft, satellites and future outposts on the moon might encounter.
Anyone venturing out tonight for the shower should look for the darkest skies they can find – well away from the urban corridor. The moon will set around midnight, leaving what should be a clear, dark, crisp winter sky for meteor viewing.
As each bit of Phaethon's rocky debris strikes the Earth's atmosphere at 35 km per second, its friction heats up the air molecules and causes them to glow, creating a bright streak across the sky. Some meteors may leave persistent trails.
You can look anywhere in the sky, but the true Geminids will appear to radiate from the constellation Gemini, rising in the east in late evening.
The best time to look is between midnight and dawn's first light. Aside from very warm clothes, a hot beverage, sleeping bags or blankets, no special equipment is needed.
"It's just really fun to get out in the middle of the night, go out in the freezing cold," Noll said. "It's an experience you're not likely to forget, even if you don't see any meteors ... The winter sky is gorgeous when it's clear."
If your skies are cloudy, or it's just too cold, you can follow the Geminids beginning at 11 p.m. Monday tonight at www.nasa.gov/connect/chat/geminids2010.html You can also go to http://fireballs.ndc.nasa.gov/ and watch the sky over the Marshall Space Flight Center in Huntsville, live as the Geminids come in.