Much of the meteor shower attention during December, and rightly so, is on the spectacular Geminids. The shower, which peaks on the night of 13/14 is a fantastic event; always reliable with many bright slow moving meteors trailing across the sky and rates in excess of 100 per hour. However, during December there is another shower worth looking out for - the Ursids. With the radiant located close to the North Pole Star, the Ursids are a Northern Hemisphere shower. They are much less dramatic than the Geminids with only about 10 meteors per hour visible. But on a few previous occasions the Ursids have shown significant bursts of intense activity and a re-occurrence may happen at any time. This year's Ursid peak occurs on December 22nd although the Moon will interfere.
The comet that sources and therefore responsible for the Ursid meteor shower is 8P/Tuttle (also known as Tuttle's Comet or Comet Tuttle). It has a period of 13.6 years and during the last perihelion on January 27, 2008 it was visible telescopically. The comet passed Earth at a distance of 0.25282 AU (37,821,000 km or 23,501,000 miles) on January 1, 2008 and anticipation was high that the 2007 and 2008 showers may produce much increased activity, but this was not to be. In the end only a small increase was noted.
The radiant for the Ursids meteors is located in the far northern constellation of Ursa Minor, "The Little Dipper". With a declination of +76 degrees, the Ursid radiant is circumpolar from most northern sites and conversely fails to rise from most southern sites. It is positioned just a few degrees northwest of Kochab (β UMi).
What to expect
The best two nights to look for the Ursids are on December 21/22 and 22/23. For this year's event, the 75% lit waning gibbous Moon will interfere. It rises in the early evening from mid northern latitude sites and remains visible for the remainder of the night. Normally the Ursids produce a ZHR (Zenithal Hourly Rate) of 10, although there have been at least two major outbursts in the past 70 years (1945 and 1986). During an outburst the ZHR can jump to at least 50, propelling the shower into the realms of some of the better annual meteor showers.
When observing annual meteors, they can streak through the sky many degrees from the actual radiant. Therefore it's best not to look directly at the radiant itself but a large surrounding area of sky. To confirm an Ursid, trace back the meteor and it will go all the way back to the radiant.
Ursids 2013 Data Table
|Meteor shower name||Ursids|
|Meteor shower abbreviation||URS|
|Radiant constellation||Ursa Minor|
|Activity||December 17th -> December 26th|
|Peak Date||December 22nd (14h UT)|
|RA (J2000)||14hr 28m|
|ZHR||10 (occasionally up to 50)|
|Notes||Compact stream with a small peak intensity window of a few hours, occasional burst in activity possible|
Comet 8P/Tuttle (at epoch October 1, 2007)
|Classification||Jupiter-family comet (NEO)|
|Discoverer||Horace Parnell Tuttle|
|Discovery date||January 5th, 1858|
|Semi-major axis (AU)||5.69986|
|Orbital period (years)||13.6086|
|Longitude of ascending node (degrees)||270.342|
|Last perihelion||January 27th, 2008|
|Next perihelion||September 5th, 2021|
|Notes||Also known as Tuttle's Comet or Comet Tuttle|