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Easy spiral galaxies?


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So far I have struggled against my local LP to find M33, M51, M101 and failed. I've not tried M33 with the same energy as the other two but my failure with them has left me feeling that the LP may be against me until I get to a dark sky site. Is it worth persevering with or are spiral galaxies not worth considering from anywhere urban (M31 excepted)?

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Hi Andrew

You've picked some toughies there. Face on spirals are tough as the light tends to be more spread out than their edge on cousins.

Out of those three M51 is the easiest having the highest surface brightness. The other two are really tough from sites with any LP. But make no mistake M51 isn't straightforward from LP skies.

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M31 and M33 are listed as the brightest, although that is magnitude not surface brightness, after that it looks like M81 in Ursa Major.which is brighter then M51 or M101.

They are all dim and all, except M31, small.

Worth looking at the Wiki page and clicking on Type to get all Spiral Galaxies grouped and checking their brightness and the image of them as you want one that is face one and displays the spiral best.

Wiki List

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As said, they are all pretty challenging except from under dark skies.

Have you tried M81/82? When abut higher in the sky they are easier i find because they are more compact so offer better contrast against the sky background.

Stu

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My 10" newtonian would show the spiral structure of M51 under really dark skies. It would not quite manage this from my moderately light polluted back garden though. With a 12" scope under the same dark skies the spiral structure was better defined and with a 20" from the same site it was really "in your face" :smiley:

M51 seems to have about the most visually accessible spiral structure of any galaxy that I can think of but I'd be happy to hear that there are ones where it's a little more obvious :smiley:

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Thanks guys and thanks for the Wiki link - it's really useful.

I'll have a look for M81 and 82 but, as with M51 and M101, they are currently too close my neighbour's house (although they were a way away when I started looking for them) - I'll have to wait for the skies to turn a little more before trying again.

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Face-on spirals are almost always hard, because you are looking at a thin layer of stars (a couple of thousand light years, tops :D). Besides, M101 and M51 are rather low in the sky, which does not help either. M74 is higher is the sky at the moment, but is a notoriously tough one as well.

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Additionally, spirals contain a lot of dust and gas (more than is found in ellipticals) which absorb starlight, hence spirals tend to have lower surface-brightness than ellipticals; comparable in fact to the surface brightness of our own galaxy, the Milky Way, which is of course a spiral. And since a telescope cannot increase the surface brightness of a target object, this means that in general, to get a good view of a spiral galaxy, you really want the Milyk Way to be visible to the naked eye. Otherwise what you tend to see is only the brightest central region, which in many spirals is effectively a mini-elliptical.

The easiest spirals tend to be ones with tightly wound arms and a large central bulge (Sa types) and the hardest tend to be ones with widely spread arms and little or no central bulge (Sc), though these are often the most photogenic, being the classic "grand design" spirals. M33 and M101 are Sc. Galaxies seen at an oblique angle can also be easier, though edge-on spirals can be difficult because there's so little of them to see (NGC 891 and NGC 4565 are showpiece examples).

M81 is type Sb, with arms wound moderately tightly and a prominent central region, and is also comparatively close - and is seen at an oblique angle. All of which make it the next best bet after M31 (another Sb).

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I have never seen spiral structure from my semi urban back yard even with my 11" SCT - and it is quite dark where I live - the sky is a mag 5.5 sky I'd say. I took this scope to the middle of nowehere and could just about pick it out in M51 and M81 but only by averted vision.

To easily see spiral structure with straight on visuals (i.e. not averted vision) you need very black skies, the likes of which are rare in the UK or a giant instrument.

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Hi Andrew

You've picked some toughies there. Face on spirals are tough as the light tends to be more spread out than their edge on cousins.

Out of those three M51 is the easiest having the highest surface brightness. The other two are really tough from sites with any LP. But make no mistake M51 isn't straightforward from LP skies.

Others with a high SB are M81 and M82 in Ursa Major, M64 in Coma Berenices (rises quite late at the moment), M94 in Canes Venatici, M65 and M66 in Leo. Virgo has quite a few too if you are prepared to be up before dawn.

I have a scope with similar light grasp in semi-rural skies and have seen well over a hundred galaxies. Granted many of them are very feint smudges. To pick targets I look at both magnitude and surface brightness. Galaxies like M101 are notoriously difficult given their bright over all light emission, due to the fact that the light is spread out over a large area.

Happy hunting!

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To put your self imposed challenge into historical perspective the first known observation of spiral structure was that of Lord Rosse in 1845, using a 72 inch reflector (though with speculum metal mirror.) It's a safe bet, therefore, that spiral structure is hard to see and that M51 is probably your best bet!

We have a 20 inch and a very dark site but spiral structure in M51, M101 and M33 can be pretty clear or not very clear at all depending on the night and, above all, the elevation of the object. When high in a clear, moonless sky the spiral structure is easy for experienced observers and sometimes easy for beginners too, certainly in M51. I never saw M101 in the UK (though it certainly can be seen) but on holiday in Spain the core was downright bright in a 120 achromat. I now pick it up in a 50mm finderscope, though only just.

Olly

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M101 and M33 can be easy in a 10x50 binocular, but only when they are high in the sky, which M101 isn't at the moment. If an object is 60* above the horizon, you are already looking through twice as much atmosphere, and it's associated crud, as you are when it is at the zenith. Above all, you need a transparent sky, with as little light pollution as possible. M33 can sometimes be seen with the unaided eye (I've only managed this once with direct vision, but I had it last month with averted). I was out with a 10x42 a few nights ago, and was surprised at how easy M63 is when it is reasonably high(never tried it before); it "grows" with averted vision.

M81/82 have had a mention: when you next observe them, try this wonderful demonstration of averted vision: get them both in the same field of view, look in the direction of M82, and watch how M81 grows and its core brightens. Then look at M81 and see how the mottling on M82 sort of "shimmers" into view.

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If an object is 60* above the horizon, you are already looking through twice as much atmosphere, and it's associated crud, as you are when it is at the zenith.

No, if an object has a zenith angle of 60 degrees, i.e. is 30 degrees above horizon, then the air mass is twice what it is at zenith. At 60 degrees above horizon the zenith angle is 30 degrees and the coefficient is sec(30) = 1.15, i.e. you're looking through 15% more crud. But you're right, the nearer it is to zenith the better the view.

After first seeing spiral structure in M51, observers using the 72 inch Leviathan at Birr Castle made a visual search for other examples, and in 1850 Rosse declared a number of galaxies to be of spiral form. For the modern observer seeking visible spiral structure these are probably the best ones to start with. A paper by Dewhirst and Hoskin (link below) gives 16 galaxies listed in Rosse's paper as spirals; one is actually elliptical, one is Sa, one is SBc and the rest are all Sb or Sc. Messier spirals in the list are 51, 58, 63, 74, 77, 88, 96, 99, 100. It is no accident that b- and c-type spirals predominate; these have the most widely extended arms.

http://articles.adsa...000259.000.html

In 1861 another Rosse paper attributed spiral structure to a larger number of objects, also listed by Dewhirst and Hoskin (link below). A few are not in fact galaxies at all, but most are, and once again Sb and Sc types predominate.

http://articles.adsa...000261.000.html

Given that these were the first to be discovered, it is probably fair to say that these are among the "easiest" spirals.

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No, if an object has a zenith angle of 60 degrees, ....

Aaargh! You are quite correct. (Brain-fuddle on rewriting something that was originally correct, but clumsy, and doing it badly; also a missing "the" in "above (the) horizon" and a bloomin' grocer's apostrophe in "it's" -- I think I'll crawl back into my pit.....)
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Have a look at East midlands Stargazers as they have a dark site near Belper and will point you in the right direction.

Indeedy. At the Ambergate Cricket ground so it's a stones throw from Belper. Not had chance to get there myself yet, one day I will!

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Thanks for such a useful and informative set of answers. Excellent!

I never quite get the time to join EMS - between work and family obligations the chance of being free on the same night as a meeting is a massive long shot. Mind you, if i could pay my dues and have access to the dark site then i'd probably join up. Cheers

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I have seen hints of spiral structure in M51 and M33 using a 10" on good dark nights. Only hints mind. I haven't seen structure with my 6" but at least M51 is quite an easy target once you know where to look and have seen it before.

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