Draconid Meteor Outburst - Comet Giacobini-Zinner

On October 8th Earth is going to plow through a stream of dust from Comet 21P/Giacobini-Zinner, and the result could be an outburst of Draconid meteors. "We're predicting as many as 750 meteors per hour," says Bill Cooke of NASA's Meteoroid Environment Office.

"The timing of the shower favors observers in the Middle East, north Africa and parts of Europe."

Every 6.6 years Comet Giacobini-Zinner swings through the inner solar system. With each visit, it lays down a narrow filament of dust, over time forming a network of filaments that Earth encounters every year in early October.

"Most years, we pass through gaps between filaments, maybe just grazing one or two as we go by," says Cooke. "Occasionally, though, we hit one nearly head on--and the fireworks begin."

2011 could be such a year. Forecasters at NASA and elsewhere agree that Earth is heading for three or more filaments on October 8th. Multiple encounters should produce a series of variable outbursts beginning around 1600 Universal Time (noon EDT) with the strongest activity between 1900 and 2100 UT (3:00 pm - 5:00 pm EDT).

Forecasters aren't sure how strong the display will be, mainly because the comet had a close encounter with Jupiter in the late 1880s. At that time, the giant planet's gravitational pull altered the comet's orbit and introduced some uncertainty into the location of filaments it has shed since then.

Competing models place the filaments in slightly different spots; as a result, estimated meteor rates range from dozens to hundreds per hour.

Comet Giacobini-Zinner, a fairly frequent visitor to the inner solar system, was captured by the Kitt Peak 0.9-meter telescope on Halloween Night 1998 (UT November 1st, from 02:07 to 03:40).

North is up with east to the left. Since the comet was moving across the sky fairly quickly, and since colour images are made by combining successive exposures through three different filters, a conventional combination would have either a streaked comet or a set of colored dots for each star.

To avoid this, the complete sequence of images, lasting over ninety minutes, was specially processed. All frames for one color were combined with filtering that removed the moving comet: this stars-only image was subtracted from each comet frame, and the comet frames were registered and summed with further filtering to remove any residuals.

The two images, with stars only and with comet only, were then added together to produce a single-color image in which neither the comet nor the stars was trailed. These three frames were then united in the final color picture, shown here.

Credit: N.A.Sharp/NOAO/AURA/NSF