Comet 21P/Giacobini-Zinner and the Draconid meteor shower
WHEN: As described, with the Draconids peaking on 8/9 October
Time is running out to grab a view of comet 21P/GiacobiniZinner. It reached mag. +7.0 last month as it tracked through Auriga and south through Gemini and into Monoceros. It was at perihelion on 10 September following a favourable close pass of Earth at a similar time, coming as near as 0.39AU or 58 million km of us.
21P is now fading as it continues south and October is your last chance to catch it for this tour before it slips below the UK’s horizon.
At 01:00 BST (00:00 UT) on 1 October, mag. +7.6 Giacobini-Zinner will be a couple of degrees south and slightly west of mag. +4.5, 18 Monocerotis. Over the following days, it continues south, passing through eastern Canis Major. On the morning of 9 October it should be around mag. +8.1 and will be 3° east of mag. +4.1 Theta (e) Canis Majoris.
Having dimmed slightly to mag. +8.4 by the morning of 13 October, the comet is in the region pointed to by extending a line from Mirzam (Beta (`) Canis Majoris) to Sirius (Alpha (_) Canis Majoris) for about the same distance again.
Tracking further south and riding along the back of the Great Dog, the comet continues to dim. By the end of October, at magnitude +9.5, it is located close to Eta (d), Tau (o) and Omega (t) Canis Majoris, which form the Great Dog’s tail. This region never gets high above the horizon as seen from the UK and represents the period when the comet will probably be lost from view.
As comets are quite fuzzy in appearance, the presence of a bright Moon affects visibility. Fortunately, the Moon will be out of the way for a large part of the month, permitting decent, dark sky views from 4-22 October.
In addition to the presence of 21P in our skies, its recent perihelion passage and close pass of Earth raises the question about whether it may enhance the Draconid meteor shower. This occurs when Earth passes through dust strewn around 21P’s orbit.
Certainly, short-lived storm level activity was seen in 1933 and 1946 with lower yet significant outbursts over other years close to the parent comet’s perihelion. ZHRs (Zenithal Hourly Rates) ranged from 20-500 or more meteors per hour over short periods.
This year, the peak of activity is expected on the night of 8/9 October. The enhancement to the Draconids’ normal 10 meteors per hour ZHR is expected to be quite subtle, perhaps raising it to something in the range of 15-50. As ever with meteor showers, it’s your observations that help refine these predictions and there’s always the chance that something unexpected may happen.