Quadrant’s kids

The meteor shower that is in progress tonight may not be as easily seen as it was last year, but it’s always worth talking about.

The peak of these Quadrantids is predicted for January 5 at around 2 hours Universal Time, which is 2 AM in Britain but 9 PM on Jan. 4 in eastern North America and 6 PM on the west coast – though Quadrantid meteors in lesser numbers may show themselves in a few preceding and following nights.

The bad news, as so often with meteor showers, is the Moon. Last year, of the three annual showers that in our time can be called the major ones – the Quadrantids of January, the Perseids of August, and the Geminids of December – the Quadrantids coincided with New Moon, the other two with Full Moons. This year it’s just the other way around. The Quadrantids’ radiant is northerly enough to be in the sky just about all night, but with it in the sky just about all night is the glare of the Moon (at its exactly Full position on Jan. 5 at 5 UT.).

An interesting but awkward thing about the Quadrantids is their name – awkward because you have to get into an explanation of it at the outset of discussing the meteors of a year. It would be easier if they didn’t exist and the year started with some Herculids or Pegasids! “Sons of a quadrant.” How can you be the son of a quadrant, and what anyway is a quadrant? (We might try to adapt Edward Lear’s nonsense poem “Who or why or where or what / Is the Akhond of Swat? Does he sit or stand or squat?” but it’s difficult to find rhymes for “quadrant.”) The Leonids are so called, “children of Leo,” because they shoot away from a radiant point in Leo, likewise the Perseids are “children of Perseus,” but there is no Quadrant constellation. But there was one once, in what is now northern Bo├Âtes, invented by Lalande in 1795 and later disused. It was one of several newfangled constellations of the Age of Enlightenment that commemorated scientific instruments; a few are still used, mostly in the deep south of the sky – Octans the octant, Microscopium, Reticulum the (optical) net. None of the other disused constellations have their names kept alive in the form of meteor-shower names.

The full name of the constellation was Quadrans Muralis, the wall quadrant. A quadrant was an astronomical instrument for measuring angular height, and a wall quadrant was a large fixed version of it. This illustration shows the ancient astronomer Ptolemy using a quadrant apparently to measure the altitude of the Moon.

PtolemyQuadrant

Yes, it is worth going out for at least a few minutes as near as you can to the time of the Quadrantids’ peak. There could be as many as three “shooting stars” a minute whose paths trace back to near the Big Dipper, so a few of them may be bright enough to be noticed through the moonlight.

2 thoughts on “Quadrant’s kids”

  1. Oops indeed. I was writing on Jan 4 and said the meteors would be “tonight” (correct) but then went and added 1. The Quadrantid peak was one calendar day later than in 2014, not two.

  2. Oops! The 2015 Quadrantid peak was actually scheduled for 02h UT on January 4 (so on the European night of January 3 to 4), not the 4th to 5th, Guy!

    As the sky was clear here in NE England for me on Jan 3/4, and despite the Moon (not to mention the cold and frost…), I had a few ten to twenty minute sky-gazing sessions just to see what was happening. Unfortunately, with the brilliant Moon and a light haze, the sky limiting magnitude was only +4.8 to +4.9, so in a total of seventy minutes scattered across the night from 22:20 to 02:05 UT, I saw just five meteors, only two of those identifiable as Quadrantids.

    However, as the pair of Quadrantids happened between 01:45 and 02:05, it would be possible to extrapolate them out to a computed Zenithal Hourly Rate of somewhere between 60-100. This is of course a hugely unreliable estimate, due in large part to the high correction factor needed to try to allow for the bright moonlight. Which is naturally why as observers and analysts we prefer dark, clear skies for meteor watching!

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