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6 inch scope; what can I see


DanyalAG

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Hello everyone I'm a relative newbie to astronomy. I have a 6 inch dobsonian. Until now, I've seen all the planets, and some DSOs. My main goal is hunting DSOs; however. My question is what is the limit of objects or detail with this instrument. I have seen the dust lanes in andromeda, as well as M33 and NGC 604. I've also seen six of the moons of Saturn. The dimmest of which was around 12.8 mag. So here are some general questions:

1. Will I be able to see Pluto from like Bortle 1 skies.

2. Will I be able to see the Horsehead nebula.

3. Will I be able to see the spiral arms of galaxies.

4. Will I be able to see 3C 273

any help at all would be appreciated 

 

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1. Yes, easily. Pluto is magnitude 14.2 I think. Under Bortle 1 skies (I wish I had some of those!) your scope should have a limiting magnitude of 15.5 or better. (Note that you won't see moons of Saturn that are this faint, because of the glare from the planet.) But Pluto looks just like a star, so either you need a star chart that goes down to about magnitude 14.5 or you need to sketch the field on two different days and see which "star" moved.

2. Do you have a hydrogen-beta filter? If so, then probably yes from reasonably dark skies. It might be doable from a Bortle 1 site without a filter.

3. From Bortle 1 skies you should be able to see spiral arms in quite a few galaxies. But I reckon from Bortle 4 you might not be able to see any at all except perhaps hints of the ones in M51.

4. Yes this is magnitude 13 so much easier than Pluto. You should be able to see it even from suburban skies. From a Bortle 1 site you should be able to see the lensed quasar J014709+463037 (Andromeda's Parachute) which is much more distant than 3C 273.

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4 minutes ago, harrym said:

1. Yes, easily. Pluto is magnitude 14.2 I think. Under Bortle 1 skies (I wish I had some of those!) your scope should have a limiting magnitude of 15.5 or better. (Note that you won't see moons of Saturn that are this faint, because of the glare from the planet.) But Pluto looks just like a star, so either you need a star chart that goes down to about magnitude 14.5 or you need to sketch the field on two different days and see which "star" moved.

2. Do you have a hydrogen-beta filter? If so, then yes from reasonably dark skies. It might be doable from a Bortle 1 site without a filter.

3. From Bortle 1 skies you should be able to see spiral arms in quite a few galaxies. But I reckon from Bortle 4 you might not be able to see any at all except perhaps hints of the ones in M51.

4. Yes this is magnitude 13 so much easier than Pluto. You should be able to see it even from suburban skies. From a Bortle 1 site you should be able to see the lensed quasar J014709+463037 (Andromeda's Parachute) which is much further than 3C 273.

^^ good answer :thumbright:

Not much I can add. 

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I do not know where the mag 15.5 limit comes from exactly (although I know limiting magnitude calculators which give this limit), but much depends on whether you are a novice or an expert. Only the latter can possibly push a clean, 6" reflector with high reflective coatings to mag 15.5 under NELM 7 skies. Pluto may be harder than expected (even in my C8, which I have pushed to mag 14 under suburban skies). However, I should be able to spot 3C273 with a 6" scope, and spiral arms of various galaxies can be seen, if conditions are right

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1 hour ago, DanyalAG said:

1. Will I be able to see Pluto from like Bortle 1 skies.

2. Will I be able to see the Horsehead nebula.

3. Will I be able to see the spiral arms of galaxies.

4. Will I be able to see 3C 273

Waht do you expect to see as Pluto? It will be a very dim dot, possibly a slight green colour but not a "planet" type object just what could be easily missed or mistaken for a dim, distant star.

You will see the nebula the horse head is in but again the horse head is small, whether or not you can pick out the actual horse head bit I wouldn't like to say.

M33 should show an arm, M51 is a possible, M61, M81, M74 look possibilities. Much will depend on the optics of the scope.

3C 273, No idea. What is it?

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From my light polluted skies I have never seen M51, M33 or the Leo trio even though I have gone from a 6 inch to a 8 inch. In the 6 inch I have seen Uranus and Neptune the ice caps on Mars and the cassini division in Saturn's rings. I also saw the 4 stars in Trapezium of orion the ring nebula M57 in Vega and the great Cluster in hercules M13. There is many more objects I have viewed with the 6 inch there is plenty out there. 

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The limiting magnitude of a 6" telescope is around 12.5 - 13 and a bit, depending on your skies. (No idea where that 15.5 comes from - a 12" will struggle to see that). Pluto is around magnitude 14.4 at the moment, so it will be a very difficult object tending to impossible.

Having said that, I *have* seen Pluto through a 6" reflector. At the time I was in the middle of the Australian Outback with spectacular skies. It was still a very hard object to see and took a lot of averted vision work to confirm it. It was magnitude 13.8 at the time.

You can see some structure in some of the brightest galaxies, but this will be hard until you've had more practice. It takes a long time to learn to use a telescope to its full advantage - just keep looking and don't give up.

If you really want to see 3C-273, it's magnitude 12.8 and quite stellar, so given good skies and good dark adaptation, you should be in with a shot, but it just looks like a 13th magnitude star amongst many other 13th magnitude stars.

Good luck - let us know how you get along.

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I was thinking of upgrading to a 10", but now that you guys say things like mag. 15.5, I think I'll stick with my scope just fine. That magnitude limit( if I can reach it) will do everything I want to do. I'll just stick with this scope and practice with it.

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15.5 is based on the assumption of Bortle 1 skies, so NELM between 7.5 and 8, and high magnification. Under most circumstances 15.5 with a 6" is out of the question. 15.5 is close to the limit of the 12" refractor in Cambridge (NELM ~6). Experience does play a big part as well, especially with seeing those spiral arms.

How often can you get to Bortle 1 skies? Where do you intend to do most of your observing?

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I can get to Bortle 1 skies, as they're in plenty in Baluchistan. Also some places have elevation of around 1500 ft. The area is arid, which will give excellent seeing and transparency.

It's around a 8 to 12 hr drive, so yes it's doable. I've been there before. It's not exactly easily accessible, but yes it can be done.

And it seems like someone disagrees with your 15.5 magnitude of my scope. Could you clarify a bit, please?!?

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I agree 15.5 magnitude is unlikely, even with 8" and depending of the pollution. If you are new at this, you have 100 bright Messier objects to look at and a large amount of NGCs, some are fairly bright and interesting too.

I saw the spiral arms of the Whirlpool Galaxy once in a rural sky, where many DSOs are naked eye visible has well has some good details from the milky way, with 8" aperture.

http://www.twcac.org/Tutorials/limiting_magnitude_table.htm

 

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You can test it yourself with this image from @John try to locate the faint magnitude stars around the Ring Nebula. It will help you defining the limits of your instrument with the pollution factor. At my rural spot with 8" I can see 3 or 4 stars  of the very faint ones, close to the nebula.

64NvI34.png

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I think the people who are saying 13th magnitude weren't talking about Bortle 1 skies. From lots of Britain, for example, 13 is a realistic limiting magnitude for a 6" scope.

Whether you can actually see to 15.5 shouldn't really matter here. The important thing is that from those skies you will be able to see some details in galaxies and nebulae with a 6" scope that are essentially impossible to see with any scope from a light-polluted sky; on the other hand, even from a light-polluted site a large enough dobsonian will show magnitude 15.5 stars.

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22 minutes ago, DanyalAG said:

I can get to Bortle 1 skies, as they're in plenty in Baluchistan. Also some places have elevation of around 1500 ft. The area is arid, which will give excellent seeing and transparency.

It's around a 8 to 12 hr drive, so yes it's doable. I've been there before. It's not exactly easily accessible, but yes it can be done.

And it seems like someone disagrees with your 15.5 magnitude of my scope. Could you clarify a bit, please?!?

I'm not being funny but if I could get under anything like the skies your describing I would get the largest scope I could afford / store / move. I've had 6" scopes under dark UK skies and yes they perform well but nothing like the marvels a 12" will show.

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13 minutes ago, DanyalAG said:

Thanks for all the great information. Another question, has anyone ever pushed a 6 inch scope to these limits?!?

I guess it's possible to reach the limits of any instruments at a place where there is no artificial light pollution, a day with no moon, perfect transparency, good seeing with low atmospheric turbulence, a place like the mountains of Chile... :icon_biggrin:

I think a good quality 6" will show many interesting things the sky even in moderate conditions, for many years, could last a life time.

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8 minutes ago, spaceboy said:

I'm not being funny but if I could get under anything like the skies your describing I would get the largest scope I could afford / store / move. I've had 6" scopes under dark UK skies and yes they perform well but nothing like the marvels a 12" will show.

You're absolutely right. I couldn't agree more. In fact I actually wanted a 10" scope. But stock dobs that size are very large and clumsy and, based on several sources, wouldn't fit in a SUV( with room to spare) I also don't have the craftsmanship to turn it into a portable trusstube, and even then their hassle factor is a lot. I live in an apartment on the third floor, so I wanted sth that could be easily transported up and down the stairs. That's why I got the 6 inch. Maybe one day, if I have the craftsmanship to build a trusstube dob, I'll buy a 10 inch. But for now, the 6 inch will do just fine. Besides, to quote Patrick Moore; 

" Under reasonably dark skies , a 6 inch reflector is the most any observer will ever need. " : )

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1 hour ago, N3ptune said:

You can test it yourself with this image from @John try to locate the faint magnitude stars around the Ring Nebula. It will help you defining the limits of your instrument with the pollution factor. At my rural spot with 8" I can see 3 or 4 stars  of the very faint ones, close to the nebula.

64NvI34.png

oh i like this!!

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