Comets are like cats

“December sees a visitor to our skies in the form of Comet 46P/Wirtanen,” writes Ken Kennedy of the Dundee Astronomical Society. “This comet was discovered in 1948 and makes a 5.4 year orbit of the sun.

“The nucleus, or head, of the comet is not particularly big but as it arrives at its closest point to the sun on this occasion it will only be around seven million miles from earth. It may sound a lot, but this is the closest it has been for many years.

“Comet Wirtanen was the original target for the Rosetta spacecraft which, because of launch delays, was sent to explore Comet Churyumov-Gerasimenko. The good news for us in the northern hemisphere is that Wirtanen will be well placed in the constellation of Taurus around its closest approach on December 16. It will be at its highest point almost due south at around 10pm so will be ideally placed for observation.

“Now for the news that may be good or bad. I once heard Patrick Moore quote the comet hunter David Levey’s assertion that ‘comets are like cats: they have tails and do precisely what they want’. This is true in relation to trying to predict how bright a comet will be.

“The estimate given for Comet Wirtanen makes it as bright as the least bright star of the Plough around the 16th and it may even be brighter – or fainter. Whichever way it goes it will be worth having a look. Don’t forget your binoculars!

“As comets are the source of many of the meteors flashing across our skies it is appropriate to continue our highlights of December with one of the finest meteor showers of the year.

“The Geminid meteor shower seems to originate from an asteroid known as 3200 Phaethon but there is a suspicion that it may be an ‘extinct’ comet. The meteor shower may be seen from December 8-17, but will be at its most active on the night of the 13/14th.

“If conditions are clear this is one meteor shower not to miss as the number of meteors per hour may reach 100, many of which are slow and bright. As always, look for these in the darkest part of the sky in your area.

“Mercury may be seen low in the south-east for a few days around December 15 when it rises about two hours before the sun. Venus will be very bright in the south south-east morning sky rising four hours before the sun.

“Mars is gradually becoming higher in the sky but is less bright than it was a month ago. Jupiter is poorly placed for observation during December. Saturn sets in the south-west at around 5pm and will be lost in twilight.

“The moon is new on the 7th, at first quarter on the 15th, full on the 22nd and at last quarter on December 29.”