Look Up Tonight! The Draconids Meteor Shower Peaks After Sunset
Look up tonight, October 7, and you might notice the sky filled with shooting stars—or you might not notice anything at all. Them's the breaks with the Draconids meteor shower, which peaks tonight after sunset, washed out slightly by a waxing crescent moon.
It wasn't always that way. In 1933, the shower was alarmingly powerful, with meteors falling "as thickly as the flakes of snow in a snow storm," and counts reported from around the world reaching 100 to 480 per minute.
Things have died down a bit since then as the Earth has crossed into less-dense fields of debris from comet Giacobini-Zinner, the source of the Draconids. Under good conditions, you might see 10 or so meteors per hour. Not exactly a "snow storm," but if you catch 10 good meteors—dust- and sand-sized particles from the comet's debris field smashing into our atmosphere and burning away—it should be well worth the wait.
You may not be familiar with Giacobini-Zinner, a lump of ice, dirt, and rock sailing through the solar system, but it means much more to humankind than the annual October meteor shower it gives us.
Giacobini-Zinner is the first cometary tail through which planetary scientists and engineers ever flew a spacecraft. This feat was the result of opportunity, creativity, trajectory witchcraft, and a willingness to act first and ask permission later.
What happened was this. Launched in 1978, the International Sun/Earth Explorer 3 (ISEE-3) spacecraft was designed to measure space weather. It was sent to the "L1 point" between the Sun and the Earth—a point exactly between the Earth and the Sun at which the two bodies have their gravitational pulls nullified and an object can thus be suspended. An object at that point thus has an orbital period identical to that of Earth. ISEE-3 was, in a sense, a space buoy whose scientific payload was chosen to measure space weather and the interactions of solar winds and the Earth's magnetosphere.
After completion of its mission in 1982, scientists and engineers proposed doing the same thing for solar winds and a cometary atmosphere. The spacecraft was not designed for this, and the maneuvers required to target and cross through a comet's plasma tail were a shade shy of impossible. Here is what the maneuvers required to complete this mission looked like:
Spaceflight isn't generally like something you might see on Star Trek. Intercept courses are almost never a straight line. You don't say, "Let's go to comet Giacobini-Zinner," fire thrusters, and move from point A to point B. Instead, the precious little fuel carried on these spacecraft, coupled with the physics challenges of gravitational attractions of bodies in space, mean that to reach a destination, you have to use little fuel and catch rides on the gravity of other bodies. These "orbital assists" allow a spacecraft to move along with virtually no fuel expended, while being accelerated simultaneously to ludicrous speeds along some precise, adjusted azimuth. Do this enough times to enough bodies and you can go just about anywhere.
There are maneuvers and there are maneuvers, and the Johns Hopkins University Applied Physics Laboratory's Bob Farquhar—the "grandmaster of celestial maneuvers"—could design maneuvers that had spacecraft arrive not only at staggeringly precise points in space, but even plan to have those arrivals take place on some particular day. (He liked to plan trajectories so that major space encounters would be achieved on days such as his wife's birthday, or his wedding anniversary.) Farquhar was responsible for the ISEE-3 plan. His elaborate maneuvers—none of which the spacecraft was designed to achieve, for a mission it was not designed to accomplish—took the spacecraft through the comet's plasma tail on September 11, 1985, making it the first spacecraft to ever do such a thing.
Farquhar then upped the ante by sending the spacecraft to comet Halley, which it rendezvoused with in March 1986. ISEE-3 then became the first spacecraft to fly through the tails of two comets. Again, this spacecraft was designed to do neither of these things. The fact that it did both is a testament to Farquhar's genius.
That's why Giacobini-Zinner is historically important and its burning-up debris worth consideration tonight, even if the dark sky won't exactly teem with meteors. The good news is that unlike many meteor showers, you don't have to stay up until midnight or later to see the main event. The Draconids shower comes alive just after nightfall. If you're unable to escape the light pollution or just don't feel like dealing with the mosquitoes, you can also watch a presentation of the meteor shower on Slooh at 8 p.m. EDT, where observatories in the Canary Islands, the UK, and Canada will be watching on your behalf. In addition to live commentary on the history and origin of the meteor shower, astronomers will offer a lesson on astrophotography and explain how you can use your DSLR to take meteor shower photographs of your very own.