April 29, 2014 – The Amazing Sky

The southern Milky Way is populated by the sky’s best clusters of stars.

Here are three of the southern sky’s best star clusters, in portraits I took earlier this month from Australia.

At top, my main image takes in a great contrasting pair of star clusters. Both lie in the constellation of Puppis, once part of the ship Argo Navis.

At left is the stunningly rich NGC 2477, so packed with stars it almost ranks as a globular cluster, not one of the sparser open clusters. At least that’s the impression it gives in the eyepiece. But instead of containing hundreds of thousands of stars, as do globulars, NGC 2477 “only” has 300 stellar members. They are just very tightly packed in one of the richest open star clusters in the sky. If it had been farther north NGC 2477 would certainly rate as one of the top 100 sky sights, and carry some memorable name after a fanciful resemblance to who knows what! Instead, it carries but a catalog number.

Next to it, at right, is NGC 2451, more typical of open clusters. It has a central bright star, this one naked eye, surrounded by 40 or so lesser stars of contrasting colour and brightness. The two clusters make a great side-by-side comparison in any low-power telescope.

Much farther along the southern Milky Way is this rich open cluster (above), NGC 6067, in Norma, itself embedded in one of the richest star clouds of the southern Milky Way, the Norma Star Cloud. Here you are gazing for 6800 light years toward the cluster which shines suspended against the background of the even more distant inner arms of our spiral galaxy.

So NGC 6067 looks a little like an island of blue stars amid the dust-reddened background of more distant stars in the Milky Way — an island in a sea of stars.