The open cluster, M47

You've got a new telescope, and you've seen the Moon and something of the planets (yes, they're small), and you're wondering about what to look at next.

If you live in the city or the suburbs, you will probably already have found that nebulas and galaxies need telescopes with large apertures, such as a Dobsonian. They will also have to wait until you can get into the country (this was written while we were still locked down in Victoria).

Instead, have a look for star clusters. They're just stars, so you can see them through the city's haze. What's more, they're pretty, and all different. Generally, they come in two classes, open (meaning scattered) and globular (meaning a swarm). Closed clusters are normally pretty small, but open ones can be large or small.


This is my photo of an open cluster, M47. The poor thing doesn't seem to have a common name like a lot of them do. Here's how to find it:

At this time of year (April) if you go out after sunset you'll probably still be able to see Orion low in the west. You'll recognise the three "belt" stars, stacked vertically. They will get a bit dim as they get nearer to the horizon. Luckily, what we're after is well above them.

Use the three belt stars to find Sirius, which should be directly above the belt. If the weather is good, you'll be able to see Sirius quite easily: it's very bright.

From Sirius, turn about 45° right and move about a quarter of the distance you travelled from the belt stars. Use my Stellarium screenshot as a guide. Start your hunt here, using your finderscope.

I've also overlaid some circles that show what size M47 is likely to be, given your focal length and choice of eyepiece. Start with a wide-angle (low magnification) eyepiece like the 25mm, and once you find it, you might like to use the 10mm for a closer view. Personally, I prefer the 25mm as it gives you a better view of the cluster surrounded by space.

My photo was taken from a dark sky site, so it's likely to be better than what you'll see visually, but when you find it, it'll be a treat.

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