Comet 21P/Gi­a­cobini-Zin­ner and the Dra­conid me­teor shower

Sky at Night Magazine - - OCTOBER / THE SKY GUIDE -

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.

The path of 21P/Gi­a­cobini-Zin­ner for Oc­to­ber, be­fore it slips out of view over the horizon

Dra­conid me­te­ors ap­pear to orig­i­nate near Nu (i) Dra­co­nis

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