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Back Garden Astronomy - Star Clusters
Back Garden Astronomy - Star Clusters

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

Groups of stars against the blackness of space, clusters make great observational targets for the amateur astronomer

M3 Globular Cluster by Doug Hubbell

M3 Globular Cluster by Doug Hubbell

When you gaze up at the night sky, it looks like a lot of stars are on their own. But a solitary-looking star may be a member of a vast group that's travelling through space as a unit. If we wind the clock back millions of years, we may find these stars forming in the same vast cloud of dust and gas.

Known as open clusters, these families of anywhere from a few dozen to a few thousand stars are created in the dusty spiral arms of our Galaxy. They travel together through space, but gentle tidal forces eventually cause the stars to move apart until they begin to merge into the general starry background.

There are many fine examples of newer and older clusters out there, perfect for looking at with binoculars. As a rule of thumb, you can pretty much assume that the younger the open cluster, the more compact it appears, since the stars haven't had much time to drift apart.

There is another variety of star cluster out there: the globular cluster. These are much bigger than the open sort, consisting of hundreds of thousands or millions of generally reddish, older stars. Whereas open clusters are found and made within the plane of our Galaxy, globular clusters form a halo around it and their creation is much less well understood.

In terms of observing, this all means that the majority of open clusters are found in or close to that misty river of stars stretching across the sky, the Milky Way, while globular clusters are seen all over the sky. When looking at them with the naked eye you'll see only fuzzy patches, but a pair of binoculars will reveal some truly spectacular gems.

What To See: Deep Sky

Outstanding Open Clusters

M45
Constellation: Taurus
RA 03h 45m 48s, dec. +24 22' 00"
The Pleiades, or Seven Sisters, is one of the most splendid clusters in the night sky. With the naked eye, six stars of the cluster are easy to see, but counting up to 10 is possible. The cluster actually contains many hundreds of stars, and a decent pair of binoculars will be able to reveal many of them.

NGC 869 and NGC 884
Constellation: Perseus
RA 02h 19m 00s, dec. +57 09' 00
This is the 'Sword Handle', a wondrous double cluster with two star clusters sitting side by side. They are both 0.5 in diameter and are easily visible to the unaided eye. Try sweeping the area with binoculars — the hundreds of stars, set against the backdrop of the Milky Way, make for a fine sight.

M7
Constellation: Scorpius
RA 17h 53m 54s, dec. -34 49' 00"
Also known as the Ptolemy Cluster, this appears to be twice the size of the full Moon. To the eye, the 80 stars of the cluster appear as a bright clump in the Milky Way, but through binoculars the stars are resolved.

M35
Constellation: Gemini
RA 06h 08m 54s, dec. +24 20' 00"
This cluster contains upwards of 200 stars and can just be seen with the unaided eye on good clear nights. Binoculars bring out the brightest 20 or so stars, while the rest form a diffuse oval wash behind.

M44
Constellation: Cancer
RA 08h 40m 06s, dec. +19 59' 00"
Known as the Beehive Cluster, M44 contains hundreds of stars and can be seen as a misty patch with the naked eye. Binoculars are the best way to see M44: through them you'll see a dozen or so of its brightest stars.

Great Globulars

M13
Constellation: Hercules
RA 16h 41m 42s, dec. +36 28' 00"
Known as the Great Globular Cluster, this is the best of its kind in the northern hemisphere. From a dark site, M13 can just be seen with the unaided eye, but its bright, round form is a stunning sight through a pair of binoculars.

M5
Constellation: Serpens
RA 15h 18m 36s, dec. +02 05' 00"
This is thought to be one of the oldest of all globular clusters. It is easily found in binoculars and has a slightly oval-shaped appearance. What you'll see is a fuzzy blob, hinting at the vast number of stars it contains.

M22
Constellation: Sagittarius
RA 18h 36m 24s, dec. -23 54' 00"
One of the brightest globular clusters, M22 is easily visible with the unaided eye, and a great sight through binoculars. It's larger than M13, which is impressive, but its place in the Milky Way's river of stars makes this a real jewel in the crown.

M3
Constellation: Canes Venatici
RA 13h 42m 12s, dec. +28 23' 00"
This is another stunning globular cluster. It can just be seen with the unaided eye, but binoculars will reveal its bright, round shape that holds around 500,000 stars. 274 of these are known to be variable, the largest number in any known globular cluster.

M15
Constellation: Pegasus
RA 21h 30m 00s, dec. +12 10' 00"
Looking like a slightly more compact M13, this densely packed object is an ideal target for binoculars. It appears as a round smudge with quite a compact central region, giving this distant star cluster a real sense of depth.

Copyright Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

Details
Date Taken: 10/07/2016
Author: BBC Sky at Night Magazine
Category: Astronomy

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