Star attraction: The brightest star clusters in the sky shine throughout summer

摘要

SUMMER NIGHTS in Australia have a lot going for them. First, they're generally warm enough to allow you to explore the night sky in your shirt sleeves. And second, you get a reasonable span of darkness in which to do it. Spare a thought for skywatchers in the latitudes of northern Europe and Canada, whose summer nights are bathed in perpetual twilight. In Australia, however, there are four hours of complete darkness even during Tasmania's shortest night. Darwin has more than twice that. This is justas well, since the night sky of the Australian high summer is perhaps the most spectacular of the year. While the Milky Way itself is not as bright as it is in the winter months (since we are now looking away from — rather than towards — the centre ofour Milky Way Galaxy), it comes with a brilliant sprinkling of foreground stars that includes the three brightest in the entire sky. They are Sirius, Canopus (both almost overhead) and Alpha Centauri (the brighter of the two pointers to the Southern Cross).