Lionising the Leonids

ASSUMING the weather gods are cooperative, just before dawn on November 18, skywatchers across Otago will enjoy the peak of the Leonid meteor shower.

With new moon occurring early on November 19, moonlight will not be a problem, so viewing conditions should be just about perfect if you want to observe a plethora of shooting stars.

The Leonids (so called because during the active period of the shower, bright fastmoving meteors appear to originate from the constellation of Leo the Lion) is one of the most celebrated meteor showers. This is because, for very brief periods in the past (for example in 1833, 1866, 1966, 1999, and 2001), there have been extraordinary outbursts, called storms, during which many thousands of meteors were observed over the course of a few hours.

I hasten to add that astronomers are not predicting a meteor storm this year; during the peak period of the shower somewhere between 10 and 15 meteors should be seen for every hour you observe.

Studies have revealed that the extreme outbursts of Leonid activity are seen when the shower’s parent object, a comet called TempelTuttle, makes its closest approach to the sun. Comet TempelTuttle is a periodic comet which takes 33 years to orbit the sun, which is why there appears to be a

33year cycle of Leonid meteor storms.

In fact, it is not quite as simple as that, and it turns out that some years, even though the comet is near the sun, a storm isn’t seen. Astronomers have found out that storms are not created by ‘‘fresh’’ material released when the comet is close to the sun, but rather debris from earlier returns, which also happens to be most dense at the same time.

Unfortunately, Earth won’t encounter any dense clouds of comet debris until 2099, so it may be some time before we witness another great Leonid meteor storm.

As our chart shows, the radiant point for the Leonid shower is low in the northeast sky in the hours before dawn. Find yourself a deck chair, wrap up warm and enjoy the show!