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 Constellation Guide ORION

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Posts : 116
Join date : 2011-08-23

PostSubject: Constellation Guide ORION   Fri Aug 26, 2011 5:15 pm

Orion - The Mighty Hunter

Pronounced "Oh - Rye - Un"

Where to find the constellation

Constellation Chart

The great hunter Orion - visible from late Autumn to early Spring, as the constellation sweeps across from South-East to South-West - is home to some of the finest deep-sky targets for astrophotographers, and visual observers alike.

M42, the Great Orion nebula, is many people's favourite DSO of all. A huge cloud of dust and gas, about 100 light-years across, and 1500 light-years away from us, is collapsing under it's own gravity, to form new stars.

The core of this stellar nursery is known as the Trapezium, because of the 4 bright (and many other not-so-bright) stars, which are the main light source of the rest of the nebula. Several million years from now, the majority of the gas will have either been used up (collapsed into new star-systems) or blown away by the stellar winds created by these new stars.

Several other nebulae reside in Orion, as well as open clusters, the red Supergiant star Betelgeuse, the famous (but difficult to spot) 'Horsehead nebula', and the nearby 'Flame', as well as the multi-coloured, multiple star Sigma Orionis.

M42 area of Orion

The huge star forming region sits amid several other treats for the visual observer

Collectively, this line of objects, extending down from Orion's belt, represent his sword.

Immediately above M42, is M43, a small 'breakaway' part of M42, situated around the 7th magnitude star 'Nu Orionis'

Above that is ngc1977, the Running Man nebula - so called because of the dark patch n the middle, which gives the appearance of a running figure - and above that is a 4.2 magnitude open cluster, ngc1981

To me - ngc1981 looks a little bit like a dot-to-dot drawing of a small crown- maybe Orion has a 'crown' logo on the handle of his sword?

Below M42 is another open cluster, enveloped in a very faint nebulosity - ngc1980, centred around the bright star Nair Al Saif.

Of these objects - the stars, and clusters are easy to see in an amateur scope - but the nebulosity of NGCs 1977, and 1980, is very difficult to spot visually

M42 and surrounds - Image by James

As you can see, the running man nebula (at the top) is MUCH dimmer than M42

The Trapezium

A group of new-born stars at the heart of the Orion nebula

4 are visible in most amateur scopes at high power - with a good quality refractor, I've also been able to detect a couple more.


Small emission nebula, located up the side of the Orion constellation

Difficult in scopes under 6", if you have any ligh-pollution - but becomes much easier to spot under a dark sky.

Near the top of this pic, you can also see the smaller, and slightly dimmer, ngc2071

Horsehead and Flame area

This image (in Hydrogen-alpha) by Andy (labelled by me) shows the
immediate area around the two nebulae, and their relative positions
compared to each other, and the surrounding bright stars.

Horsehead nebula

Image by Andy - The Horsehead (also known as Barnard 33 - B33) is a patch of dark dust, as seen against the background of the brighter diffuse nebula IC434

IC434 is VERY faint, so detecting the Horsehead visually is a REAL challenge - pretty much the 'Holy-Grail' of visual observing -
combination of large aperture, great sky, filter, and good 'averted vision' technique, is needed to even stand a chance of marginal detection.

Also best to keep the glare from Alnitak outside of your field of view.

Flame nebula

Image by James - Located right beside Alnitak - another very faint nebula - although no as difficult visually as the Horsehead.

Another one that benefits from keeping Alnitak outside of the field of view


Red supergiant star - about 425 light-years away - this star has used up all of it's hydrogen fuel, and is now fusing heavier elements - the outer shell has grown so bloated that if it were in the centrte of our solar-system, all the planets out as far as Jupiter, would be within it's distended outer layers.

It is already in the carbon-burning stage of it's life cycle, so it is expected to explode in a type 2 supernova, in a thousand years or so - when this happens, it is expected to be about as bright as the Moon, and visible in daylight, for a few months.

Collinder 70 (Cr70)

Huge, very distended open cluster - situated around the stars of Orion's belt - most of the stars in this area - a circle roughly the same
diameter as the width of the 'belt', and centred on the belt's middle star Alnilam - are members of the cluster.

Collinder 69 (Cr69)

Another large open cluster - although not as large as Cr70 - centred around the star 'Miessa' which marks the hunter's head.

Sigma Orionis

A multiple star, just below the left-hand belt star (Alnitak) and quite close to the Horsehead.

4th Magnitude white primary - with 7th mag red star, 13 arcsec to it's East - and a 7th mag blue star, 42 arcsec east - there's also a 10th mag white star, 11 arsec over to the West of the primary

Orion NGCs (with magnitudes) - from my own "1200 Northern NGCs" list

For those with 'GoTo' or a good chart

1662 - OC - 6.4

1684 - Gal - 12

1691 - Gal - 12

1973 - Neb - 7

1975 - Neb - 7

1976 - Neb - 4 (M42 - Orion nebula)

1977 - Neb - 7 (Running Man nebula)

1980 - OC with Neb - 2.5

1981 - OC - 4.2

1982 - Neb - 9 (M43)

2022 - PN - 12.8

2024 - Neb (Flame nebula)

2068 - Neb - 8 (M78)

2071 - Neb - 9

2169 - OC - 5.9

2175 - OC - 6.8

2194 - OC - 8.5
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PostSubject: Re: Constellation Guide ORION   Fri Aug 26, 2011 5:43 pm

Excellent job!!! WOW, I didn't realize that Orion was so full of stuff - I know I will be using this guide....

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PostSubject: Re: Constellation Guide ORION   Fri Aug 26, 2011 5:43 pm

There's an enormous complex of gas and dust in Orion. It sits on the edge of a huge bubble, blown outward by an ancient supernova. That's what makes all these cool things to look at.

The Horsehead nebula is a nearly impossible target visually
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PostSubject: Re: Constellation Guide ORION   Fri Aug 26, 2011 5:44 pm

astro_alan wrote:
The Horsehead nebula is a nearly impossible target visually

I was in two minds about including the Horsehead in this guide.

But because it's so well-known, beginners do ask obout it fairly often, and you end up explaining over and over again, how hard it is to detect visually - so in the end, I decided to include it, then try to convey just how difficult it is to give yourself even a very slim chance of seeing it.

Never seen it myself either - but we live in hope....

(hence the term 'visual Holy Grail') Very Happy
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PostSubject: Re: Constellation Guide ORION   Fri Aug 26, 2011 5:45 pm

That was very interesting as I was out last night with my new bino's (purchased from Lidl) looking up at Orion and trying to find my way around the various stars etc. This guide will really help.
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PostSubject: Re: Constellation Guide ORION   Fri Aug 26, 2011 5:47 pm

Thanks for a great guide.
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PostSubject: Re: Constellation Guide ORION   Fri Aug 26, 2011 5:47 pm

One of my favourite constellations. I only use bins for sky watching as it is a new hobby and Orion always reminds me of an explosion with the four main stars around the belt shooting out! It kind of leaps out at you. Well I think it is quite impressive......
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PostSubject: Re: Constellation Guide ORION   Fri Aug 26, 2011 5:48 pm

Thanks for this information it is fantastic, just the sort of thing I can print off and take out with me. There is so much to help get the best from each constellation. Wish I hadn't bothered with a goto mount now as no need with this sort of detail available! Much better than any book I've seen - would make a great book though. Very Happy
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