Through the smokehole

Winter shower par excellence: that’s what the Ursid meteors of December 22 are.

In time they arrive closest to the longest night of the year, and in space they come from near the north pole of the sky – only 12 degrees from it. So this radiant of theirs (the point from which they seem to shoot) is in our sky all night, though highest at dawn, when indeed it is about overhead. The Ursids’ trails are the likeliest to be entirely above the horizon.

It’s rather as if the celestial dome is an igloo and these sparks are coming in (instead of going out) through the smokehole. My simile is a little spoiled because igloos, unlike Navajo hogans, don’t have smokeholes, though some of them have ice-covered windows.

It’s a pity that the Ursids aren’t very abundant, and that few but Eskimo people may be hardy enough to be out of the igloo and looking skyward!

UrsidChart
The radiating lines indicate the radiant, but actual meteor trails are likely to be far away in other parts of the sky.

Ursa Minor, the Little Bear, also informally known as the Little Dipper, has only two brightish stars: the Pole Star (Alpha Ursae Minoris) at one end and Kokab (Beta UMi) at the other. Both are close to magnitude 2.0, Polaris a hair brighter, the exact values differing in various catalogues. The Ursid radiant is near Kokab; actually the position given is closer still to the fainter star just northwest of Kokab, but radiants are really patches of sky rather than exact points.

Everyone knows the Pole Star, few have heard of Kokab, though one distinction it has is that it’s the only star whose name means just “star.” Arabic has two words for “star”: najm (in Egypt nagm) and kawkab. Kokab is what the latter becomes in post-classical Arabic. Hebrew has the same word, becoming kokhabh or, if you like, kochav, meaning that the middle and final consonants became fricative. Belvoir, a Crusader castle that looks down from the eastern flank of Palestine onto the Jordan valley, is called in Hebrew Kokhav ha-Yarden, “star of the Jordan.”

I’ve remembered that I’m wrong: there is one other star called just “star,” and it is in the same constellation: Delta of Ursa Minor, next to the Pole Star and fainter than magnitude 4: it is said to have the name Yildun. Whoever gave it this name must have done so as a kind of nod to Kokab, and must have intended the Turkish word for “star”: yildiz, where the i’s should be dotless, representing the Turkish vowel that is at the back of the tongue.

To get back to the Ursid meteors, just in case you think of sallying from your igloo to see them: there is more about them (and the comet from which they derive) in the meteor section of the Astronomical Calendar. Their peak (only up to about 10 an hour) is predicted for about 20 Universal Time, which is 8 PM for Britain but 3 PM for eastern North America, so you may be seeing them after the peak (and they can straggle on till about Christmas day). The Moon is out of the way, being New today.

2 thoughts on “Through the smokehole”

  1. Interestingly, it seems the Ursids did produce another outburst this year, as first reported by the Canadian CMOR meteor radar based at London, Ontario. There’s a graphic showing the radiant detected with some comments by CMOR director Peter Brown on Spaceweather.com for December 24 and 25. Judging by this and the early reports arriving on the Meteorobs e-mail noticeboard, the event seemed to have peaked around 00h UT on December 23, perhaps lasting for an hour or so (elevated meteor counts seemed to have been present between very roughly 23h and 01h UT on Dec 22/23). The Zenithal Hourly Rates may have been circa 40-50 at best, and probably fairly briefly (maybe only half an hour) although this is just a first estimate. Some of the visual reports suggested the meteors were predominantly fainter than magnitude +3, though not all the sightings so far have agreed with this assessment.

    Meteor scientist Jérémie Vaubaillon had predicted a possible outburst around 00h40m UT on Dec 23 due to the dust laid down by the shower’s parent comet 8P Tuttle during its perihelion passage in 1392, although he was uncertain in advance if enough dust would have survived from then to make much of a display in 2014. Apparently it had!

  2. One’s got to be a bear to go out this time of year to look for meteors. If skies were clear, I’d be out there now, but alas, the drear and drizzle keep me in my warm apartment over a pot of lamb stew.

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