Sunday, June 19, 2011

A very beginner’s guide to M6 and M7

As the title says, it’s a super beginner guide, perfect for you who got your first telescope when the Summer constellations swings by and you’re bored of pointing to the Moon and Saturn and Jupiter. (This assumes that you know how to turn the knobs already). Now it’s high time you finally grow up and search for the true astronomer’s treasure – the Deep Sky Objects. In this case, M6 and M7 are both open star clusters. You can read more about open star clusters and their significance at

Well then,

First off it’s M7. The trick here is partly contributed by my friend Tan Simpson. As in any guides that I’ll churn out soon (hopefully) most of them will be based on starhopping. All pics by Stellarium, a free star chart software that you SHOULD get here -


1. Find the constellation Scorpio. It can be easily identified by the red star Antares at the centre, and after you spotted it, simply glance at your star chart or stellarium and then look back at the sky and play connect the dots in your head.

2. Now zoom in to the tail of the Scorpion, there is two *quite* close stars there. No they are not double stars, a double star is much closer.


3. There. As the picture suggests, just make out an imaginary line and use the finderscope to navigate your way to M7. If you live in a fairly polluted area M7 might not appear in your finderscope, otherwise it is visible as a faint patch of light (magnitude 3.3) Therefore the two stars circled in red are for distance reference. 

4. Identification of M7. I use the shape of the centre of this star cluster.


It’s not something random, it’s a Chinese character 不 that means ‘no’. Okay it’s random, but this is gonna help you into finding your next target.

Well then, pause for a while and gaze at this beautiful star cluster, discovered by Ptolemy in 130 AD and described as ‘the nebula that always followed Scorpio’s tail’. Obviously it is not a nebula, but telescope observations didn’t take place until the 1600’s. And Charles Messier made it his 7th celestial object of comet wannabes.

Well then, let’s move on.

5. Now you follow the path where 不 is pointing to. This is a little bit tricky as M6 is not directly straight to the line. Or rather, you use this line which is the in-between of the two lines in bold.


I used the finderscope to navigate through this and got lucky to see M6 in the finderscope itself. Usually M6 is not as bright because it’s a magnitude 4.2. Bear in mind that magnitude is calculated on a logarithm function, implying that a mag 4 is about 10 times darker than a mag 3.

6. Identify M6 a.k.a. the Butterfly cluster

This you can’t go wrong.


The “Butterfly cluster” is named so because it resembles a butterfly. See the two butterfly wings spreading out? This is what I see under 24x magnification. Another notable thing is the red star BM Scorpii that really contrasts his blue neighbourhood. BM Scorpii is also a variable star (a star which brightness changes), the range changes within magnitude 5.5 to 7.0.


Now this is also my first two Messier objects, so essentially we’re learning together :P My next target is the densely populated Sagittarius region, hopefully I can make out more comprehensive guides to the Deep Sky Objects! 

Any suggestions and improvements, do not hesitate to comment too!

Clear Skies!

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