Crab Nebula

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Crab Nebula

Postby Aratus » Tue Nov 29, 2016 11:42 pm

Clear night skies at last, but freezing temperatures to go with it. From 10pm onwards the sky became very transparent. Just the sort of conditions to go hunting for the dimmer Messier objects. The Crab Nebula (M1) was one of those objects that hid from me for decades. It has a low surface brightness that easily disguises itself. It isn't particularly large either. It wasn't until I obtained an 8" 'goto' telescope 12 years ago than I finally cornered it. It isn't very impressive - a grey oval that's all - but it is the remnant of a super nova.
On this occasion I tweaked the tracking and took some 45 sec exposures. The next day I stacked 8 of them, and pulled out some detail. You get some idea of the structure which reminded The Earl of Rosse in the 1840s of a crab. His telescope was 30 times bigger than mine in area! The wonders of modern technology! :)

Image

This is using a 6.3 focal reducer.
I use an 11" Celestron SCT (CPC 1100) on an equatorial wedge, housed in a 2.2m Pulsar observatory. I use a ZWO ASI1600MC and Canon 500D for imaging.
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Re: Crab Nebula

Postby Gfamily2 » Wed Nov 30, 2016 10:30 am

Aratus wrote:Clear night skies at last, but freezing temperatures to go with it. From 10pm onwards the sky became very transparent. Just the sort of conditions to go hunting for the dimmer Messier objects. The Crab Nebula (M1) was one of those objects that hid from me for decades. It has a low surface brightness that easily disguises itself. It isn't particularly large either. It wasn't until I obtained an 8" 'goto' telescope 12 years ago than I finally cornered it. It isn't very impressive - a grey oval that's all - but it is the remnant of a super nova.
On this occasion I tweaked the tracking and took some 45 sec exposures. The next day I stacked 8 of them, and pulled out some detail. You get some idea of the structure which reminded The Earl of Rosse in the 1840s of a crab. His telescope was 30 times bigger than mine in area! The wonders of modern technology! :)

Image

This is using a 6.3 focal reducer.

That's a very nice image
I tried to set up for observing, but we had a lot of high level haze which gave a fairly 'brown' sky. In addition, my alignment wasn't great, so it was all a bit disappointing.

If you want a 'fun fact', the Hubble Ultra Deep Field image approximately corresponds to an area of the sky that would fit between the two stars roughly half way down the Crab Nebula.

Another fun fact is that astronomers used the Chandra space telescope to take an X-ray 'image' of the atmosphere of Titan when Saturn's moon transited the Crab Nebula in 2003.
Scopes: Meade 8" SCT, Skywatcher 127mm Mak, Raffle winner of SW ST80
For imaging: Pentax K5, Asda webcam, Star Adventurer (new toy)
For companionship: Mid Cheshire Astronomical Group.
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Re: Crab Nebula

Postby andrewscomputers » Wed Nov 30, 2016 4:14 pm

Hi Aratus a good image I have always tried to find it but I failed,but I did use my camera again on M34 and did manage to get about fifteen stars in view.I managed to cut the chip noise by enabling the dark frame correction and just getting the stars.
Thks
Andy
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Re: Crab Nebula

Postby Aratus » Wed Nov 30, 2016 6:32 pm

Gfamily2 wrote:I tried to set up for observing, but we had a lot of high level haze which gave a fairly 'brown' sky. In addition, my alignment wasn't great, so it was all a bit disappointing.


It was like that for me last night. The sky was clear enough but a high level haze washed out any deep sky objects. It would probably have given good views of planets though - if there had been any to see.

andrewscomputers wrote:Hi Aratus a good image I have always tried to find it but I failed,but I did use my camera again on M34 and did manage to get about fifteen stars in view.I managed to cut the chip noise by enabling the dark frame correction and just getting the stars.
Thks
Andy

What kind of exposure times are you using? You will need 5 to 30 seconds to get a useful number of stars.

My 8" SCT can pick up the Crab every time, but I never did see it in my 6" reflector, although I should have been able to. The Canon doesn’t seem very sensitive to its light, but my old Meade DSI used to give very bright images of it, albeit not at a good resolution.
I use an 11" Celestron SCT (CPC 1100) on an equatorial wedge, housed in a 2.2m Pulsar observatory. I use a ZWO ASI1600MC and Canon 500D for imaging.
Aratus
 
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Joined: Tue Jan 12, 2016 2:17 pm
Location: East Lincolnshire

Re: Crab Nebula

Postby andrewscomputers » Wed Nov 30, 2016 6:51 pm

Hi Aratus thanks for the advice I will try again as it is still a steep learning curve with the camera.I now my gain was fully up and the exposure was short to get the image in focus,I did use a focal reducer.I now the club I go too everyone that does imaging uses a Refractor and not a reflector,so I think I have chosen the hardest task in my scope.
Thanks
Andy
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Re: Crab Nebula

Postby Aratus » Fri Dec 02, 2016 1:53 pm

A short exposure won't improve the focus, although having too large an exposure will cause stars to 'bloom' and look large. That can make it harder to focus. Put the gain on about 3/4 and use the exposure control until you have a grey sky. Then focus until the stars are as small as possible. Then put the gain down to 1/2. Then experiment with exposures starting with 10 seconds and go up by 5 each time.

Just remember that people often justify their own choice of equipment so take recomendations with a pinch of salt! Refractors have an edge with planetary images, that's true, but while they are messing around with their 'keyhole' telescopes trying to find and fit an object into their narrow field of view, you can do much better with your reflector.

If you want an easy object to start with go for something like the Orion Nebula. It is bright, easy to find, and it is easy to get stunning detail. A reflector will do far better than an average refractor on that object.
I use an 11" Celestron SCT (CPC 1100) on an equatorial wedge, housed in a 2.2m Pulsar observatory. I use a ZWO ASI1600MC and Canon 500D for imaging.
Aratus
 
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Joined: Tue Jan 12, 2016 2:17 pm
Location: East Lincolnshire

Re: Crab Nebula

Postby andrewscomputers » Fri Dec 02, 2016 7:26 pm

Hi Aratus thanks for the advice,I will have a go at m42 when the skies are clear again.I did see the M42 the other night in the trapezium with the four stars and the nebula surrounding them with my 0111 filter.I have just managed to work out all the constellations and where to find the messier objects.
Thanks
Andy
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