The Ursids

The Ursids are a December meteor shower. They get their name from the position of their radiant, which is in Ursa Minor. The closest major star to the radiant is Beta Ursae Minoris (Kochab), but I was wondering if I could come up with a more accurate position.

After searching around for a bit, I found a pretty good post which gives loads of historical calculations of the Ursids' radiants, and I plotted these all onto a chart for comparison:

[Ursids Radiants map]

The observations appear to centre somewhere between Vanysek (RA 217.8°, Dec 76.7°) and Jodrell2 (RA 207.1°, Dec 77.6°). Ceplecha used photographic plots and is rather close to the centre of the combined observations too. Note that Hoff5 and Jodrell1, 3, and 4 are classed by the IAU as being in Camelopardalis rather than Ursa Minor. Hoff2 is extremely close to the border with Draco.

The KML source is UrsidsRadiants.kml, which can be used for plotting into Google Sky. The chart above is from Google Sky, with some post processing in Gimp to swap the colours around (red for the azimuthal grid? ugh!). Sorry that it's a bit fuzzy. I don't know how to plot things in Stellarium, if it's even possible, which generally gives a clearer chart.

Calculating when the meteors will appear is kinda tricky since they often come only in a very narrow window around the maximum, but it's generally on 22nd December.

Sean B. Palmer