What galaxies can I see? 4.5 dob

[Manok101]

I was just wondering other than andromeda what galaxies can I see with my 4.5 inch dob?

[johnh]

Have a look at Andromedas 2 satellite galaxies which should be easy M32 and M110. There are quite a few others, M101 and M33 are big faceon so tricky but a low widefield power should give you a glimpse with averted vision as they are not well detached from surrounding sky. M81 should be easy but try M51, M63 and M94 in Canes. Galaxies with high surface brightness like M82 near M81, M94, M64, M77 perhaps M104 lower down near Corvus worth a try. Many of 9th mag will be very difficult but some may be seen with averted vision so give them a try - you will need good transparent skies. Virgo has some bright 9th mag elliptical galaxies like M49 + M87 and M86+M84 worth a look with averted vision. I am sure there are many more than these you should be able to see.

There are lots out there worth a try but 4.5" will limit you but there are sights out there then you may be interested in a 8/10" or a big 12" which is what lead me to the larger sizes but 4.5" scope is still useful as an introduction.

Enjoy, John.

[Doc]

Not many if you live under light polluted skies, the only galaxy you will see easy is M31. Under dark skies then quite a few will appear such as M51, M81/82, M49, M84/85.

[umadog]

NGC 253 (C65) - the silver coin galaxy. Bino object given suitable skies, although it's South and nearish the horizon. You should tell us how dark your skies are, however. That will make a great deal of difference with galaxies. With suitable skies you'll be able to see all the objects in the Messier catalogue and most from the Caldwell. So you should, given dark skies, also be able to see NGC 7331 (C30), NGC 891 (C23), for example. They'll be very faint, however. M82 has quite high surface brightness and so should cope with light pollution fairly well. I think M51 and M33 will be killed off for you in Mag 4.5 and worse skies. Definitely re-visit targets in darker skies. You'll see more.

[acey]

I was just wondering other than andromeda what galaxies can I see with my 4.5 inch dob?

It entirely depends on the darkness of the sky. In daytime you'll see none. If your night sky is dark enough for the Milky Way to be visible naked eye then you'll be able to see all the Messier galaxies and many NGC objects.

If M31 looks little more than a faint fuzzy blob through your scope then a light sky is hampering you. As mentioned, NGC253 is the next best to look for, if it rises high enough in your sky (from UK it never rises high but in southern US it does). M81/82 are also bright and easy.

If light pollution is a problem for galaxy viewing then larger aperture won't solve it. Better to take your small scope to a darker site. Unlike stars, galaxies aren't made brighter by a telescope, just bigger. If there isn't enough contrast against the sky then no aperture will make it visible. As I said, you can't see galaxies in daylight.

Incidentally, NGC 253 was discovered from Britain by Caroline Herschel using a 4" scope.

[mdstuart]

Of course it depends on the time of year...but from my observations.

In approximate order of difficulty

Brightest is M31

Then M81,

Then M82,M104,M32,M49,M64,M82,M94

A little more challenging M106,M51,M63,M77,NGC2901

Harder again M110,M33,M59,M65,M66,M87,NGC3521,NGC2403...

All of the above are visible in 80mm bionculars from a semi urban sky (mine north of Bristol)

However there are about 60 more which I would class as relatively easy with a 4.5 inch dob..

Enjoy!

Mark

[mdstuart]

Sorry I ment NGC 2903 not 2901...Its in Leo so rising after midnight at the moment but getting earlier by the day!

Mark

PS I have not managed NGC 253 mentioned above as its always low from the UK in the murk at my site

[acey]

I have not managed NGC 253 mentioned above as its always low from the UK in the murk at my site

I've viewed it with an 8" from UK and it wasn't hard, though the low altitude does compromise the view severely. But from more southern latitudes it's a splendid binocular object.

[Manok101]

I dont know how to figure out my limiting magnitude, but I can see the bright constellations just fine like, orion, canis major, the charioteer(can't spell the real name for the life of me), taurus, and gemini, but cant see cancer leo, lynx with my eyes, however with my telescope I can see nearly all constellations depending on time of night.

[umadog]

Here's the geeky science bit.

To clarify what acey says: a telescope will make all objects brighter; both stars and galaxies. It must because they all emit photons and a bigger collector always gathers more photons. Apparent brightness increases with photons collected. Naturally, increasing aperture increases a galaxy's apparent brightness. However, what acey is getting at is that galaxies are diffuse objects with low surface brightness whereas stars are point sources with high surface brightness. Therefore, under light polluted skies it is easy for the sky background to approach or exceed the light from a faint galaxy. When this happens no telescope will ever reveal it to you because it has been over-powered by the sky glow. In other words, there is not sufficient contrast between the galaxy and the surrounding sky for your eye to see it. Although note that with a better detector, such as a long exposure CCD camera, the galaxy will once more be visible. The signal to noise constraints of the detector determine at what point the galaxy will cease to be visible. During the day the sky glow is so great that one can, of course, no longer see the stars; they are now over-powered too and for exactly the same reason as the galaxy was by light pollution. With an ideal detector (which does not exist!) the stars would be visible during daylight.

To put all that another way: a telescope makes everything brighter, including the sky itself. Therefore, whilst it increases brightness globally, it can't increase object-sky contrast. It's contrast that's required for you to see stuff. Note that there is a perceptual improvement in contrast for brighter objects at higher powers as the exit pupil becomes smaller but this is probably because the image becomes globally dimer, making the sky darker. This latter effect, and also everything else outlined above, is ultimately related to something called the Weber's Law http://en.wikipedia.org/wiki/Weber%E2%80%93Fechner_law

Weber's law is ultimately the reason why the stars aren't visible during the day.

[acey]

Yes, to clarify what I was saying: by "brightness" I mean surface brightness, which is the relevant parameter in relation to viewing galaxies (as opposed to integrated magnitude). Stars are effectively point sources, galaxies are extended objects. Magnification doesn't (significantly) increase the size of (effective) point sources but does increase the size of extended objects, thus reducing their surface brightness.

Specifically, for a telescope of aperture A, and eye-pupil diameter p, we can define the light grasp G = (A/d)**2. When a galaxy is magnified in a telescope by a factor m, the total (integrated) brightness of its image is multiplied by G, while its area is multiplied by m**2. Hence its surface brightness is multiplied by G/m**2. But the lowest useable magnification is (A/d), hence the surface brightness is multiplied by a number less than or equal to one. The telescope makes extended objects larger but no brighter (in the sense of surface brightness); the advantage of aperture is that it minimises the amount of dimming (i.e. reduction of surface brightness).

Contrast remains unchanged by magnification (because object and sky are dimmed equally) but the human eye perceives faint objects best if they are around half a degree in apparent angular size. A telescope enables us to magnify galaxies (or details in them) until they reach this sort of size. A large aperture scope enables higher magnification with less loss of surface brightness; hence small, faint details become more apparent. But all of that is assuming that there is sufficient contrast of object against sky to begin with: the scope can't change that.

Or to put it very simply (again): you can't see galaxies in daytime, no matter what aperture you use. So, to the question, "What galaxies can I see with a 4.5" scope?", the answer is: "It depends how dark the sky is."

[mdstuart]

To work out your limiting magnitude...look at Pleides M45 the bright cluster to the E early in the evening and draw the stars you can see..

Then compare with ..

http://www.arksky.org/images/pleiades.jpg

My 110mm TAL was 11.8 my 250mm scope is about 14.0

Mark

[Capricorn]

Seems that your scope should have a limiting magnitude = 12.4, resolving power = 1.0 arc seconds.

Here are the messier galaxies that are rated as Mag 10 or brighter. Assumed that the limiting Mag is a little optimistic.

M31---- Andromeda Galaxy ------- Andromeda --- 3.5

M33 --- Triangulum Galaxy -------- Triangulum --- 7.0

M51 --- Whirlpool Galaxy ---------- Canes Venatici --- 8.0

M63 --- Sunflower Galaxy --------- Canes Venatici --- 8.5

M81---- Bode's Galaxy ------------- Ursa Major --- 8.5

M83 --- Southern Pinwheel Gxy ---- Hydra --- 8.5

M101--- Pinwheel Galaxy ----------- Ursa Major --- 8.5

M64 --- Black Eye Galaxy ---------- Coma Berenices --- 9.0

M82 --- Cigar Galaxy ---------------- Ursa Major --- 9.5

M94 ---------------------------------- Canaes Venatici --- 9.5

M104 -- Sombrero Galaxy ---------- Virgo --- 9.5

M106 --------------------------------- Canes Venatici --- 9.5

M32 ---------------------------------- Andromeda --- 10.0

M49 ---------------------------------- Virgo --- 10.0

M66 ----------------------------------- Leo --- 10.0

M110 ---------------------------------- Andromeda --- 10.0

[acey]

Leo I is mag 11 and I've never yet managed it with a 12". On the other hand, there are galaxies with integrated magnitude 15 that I've seen without difficulty. As I said, the important thing for galaxies is surface brightness (of object and sky), not magnitude.

[Capricorn]

Acey, agreed surface brightness is better.

Please supply a suitable list for Manok of them to observe.

I simply found the easiest one I could.

Will make use of your list myself as it will be useful.

[acey]

A list is not helpful, because surface brightness varies across the object. The cores of galaxies reach surface brightnesses of 16 mag/square-arcsecond or brighter, while the outer parts can be fainter than 24 mag/square-arcsecond. Taking an average surface brightness across the whole galaxy is therefore of limited use.

Detailed mapping of surface brightness has only been done for certain galaxies. However, in 1975 the astronomer Arakelian compiled a list of "high surface brightness galaxies" drawn from the Morphological Galaxy Catalog, using particular criteria. There are about 600 objects in the list, some of them well known (e.g. M32) but most very small and therefore beyond the reach of small scopes.

The list is here:

Your NED Search Results

In practice you've just got to give things a try. In a dark sky the whole Messier list is within reach of a 4" scope, in a bright sky it's not.

[mdstuart]

Hence my list earlier which was based on visual observations...

Mark

[LukeSkywatcher]

I have seen the triplet in Leo with a pair of 20X90 bins. They were faint but very galaxy in appearance. So a 4.5" scope will show those.

[mdstuart]

Paul

Yes M95/96 and NGC 3628 are in my "60 more" list I noted. They are tougher than M65/66. In fact I would say NGC 3628 is very tough unless you have dark skies as it has a low surface brightness.

A lovely Triple!

Mark

[mdstuart]

Here is my lastest list of galaxies viewed and still to view. Anything listed with a visual scale of 2 or higher will be visible in the 4.5 inch scope!

https://spreadsheets.google.com/ccc?key=0AjYp5nWTbPIidDlJUDhDLWRTdlBNVUVCaWZiNmxoeEE&hl=en

Mark

[Manok101]

Will I be disappointed if I get a bigger scope? or will not even a 10" dob help?

[acey]

Manok101: How dark is your sky? (And what's your latitude?)

Mark: your list is very interesting and useful, but also needs to be interpreted appropriately. Ranking DSOs by visibility has been done since the time of William Herschel: he graded more than 2000 galaxies as "bright", "faint" or "very faint", calling them class I,II or III. His son John further developed this as the ranking that went on to be used in the NGC. So on the face of it I ought to be able to look in the NGC and use the brightness ratings there as a guide for viewing. In practice this doesn't work out.

Analysis of Herschel's rankings shows many discrepancies and anomalies: he even accidentally classified some objects more than once, assigning them to different brightness classes. It's easy to see why this can happen. Factors afflicting any attempt to list DSOs by brightness include:

1. Surface brightness versus size, in relation to aperture and sky brightness. At a very dark site I may be able to see M33 with the naked eye, but can't see M81 with the naked eye. In a suburban back garden with a telescope I may be able to see M81 easily but M33 not at all.

2. Declination and latitude. An object seen low in the sky is greatly dimmed. You mention that you can't manage NGC 253, but for a more southerly observer it will be one of the easiest objects in the sky.

3. Local conditions. Transparency varies from night to night, hour to hour, and from one part of the sky to another.

4. Subjective factors. It gets harder when we're tired.

All of these factors affected William Herschel's list and every list that followed, including the NGC, and presumably your own (as well as my own rankings which I make in the course of my observations). I think it's very valuable for people to gather data on DSO visibility, but I also think it's easy for beginners to be misled into thinking there is some kind of objective ranking that will tell them what they can or cannot see. Attempts to model this mathematically have been made, the most sophisticated being the work of Roger Clark, who gives a very big list of DSOs in his excellent book (sadly out of print), Visual Astronomy Of The Deep Sky. As well as his own observations he offers visibility ratings for various apertures and sky conditions based on his theoretical model.

Clark's work has been very influential and much admired, but it does not really offer the perfect guide to visibility that everyone seems to want. Every observer will find their own ranking, based on their location, sky brightness, equipment used and visual acuity. I applaud anyone who compiles and shares such data, but will always urge caution in the interpretation.

Clark's list of what he considers the "most interesting" DSOs (611 objects) is here:

http://www.clarkvision.com/visastro/appendix-e.html

It includes surface brightness and contrast data. This needs to be carefully intepreted because, as I mentioned previously, surface brightness is not constant across the whole of an object. In the end there's only one way to know if a given object will be visible through a given scope from a given location, and that's to try it for yourself.

What we can, however, say with a degree of confidence, is that if the sky is bright (such that the Milky Way is not visible to the naked eye), then galaxies will always be somewhat underwhelming, with any aperture. But if the sky is truly dark then increasing aperture will show an ever increasing amount of detail. As Clark says in his book (p244): "For deep-sky work, a 4-inch telescope in the country will beat a 16-inch in the city."

[SiriusB]

Will I be disappointed if I get a bigger scope? or will not even a 10" dob help?

That does depend rather on how dark your skies are.Galaxies can be rather elusive creatures.

I'd persevere with your 4.5" for a while- maybe take it out into the country to see what improvement you get, as suggested previously?.

I've seen a good few galaxies with an 80mm from the back yard- persistance is the key, what you can't see one night may show up another night when conditions are more favourable.

Try different magnifications- this can make or break on some objects.

Ultimately if galaxy hunting is for you, a larger telescope (8"plus) would be advantageous- but time spent exploring the limits of what you can see with the 4.5" would be time well spent & the experience pay you back richly should you decide to get something larger in the future. IMHO.

[mdstuart]

Acey

Very much agree with your last post. I have Clarks book....

I have found that the NGC data of vB and vf etc is often very much adrift from what I have found at the eyepiece.

The fun for me is hunting and finding these galaxies! I do enjoy though categorising them. My list will be very much affected by angle of viewing, weather, how long I have been outside to get dark adapted etc etc so my list is just as non-objective but hey its all my own work.

Regards

Mark

[mdstuart]

Acey

I plotted my brightness rating against Clarkes surface brightness calc and there is some correlation between the two but it is limited.

Quite facinating. He lists M32 and NGC 3396 as the same surface brightness of 20.7. I list M32 as a very bright rating 3 with NGC 3396 as a very faint <0.5..

Now I appreciate that NGC 3396 is much smaller but even at the power of 154x as in his noted whatever measure you use M32 is MUCH brighter visually than NGC 3396.

Perhaps I will have to come up with a Mark Stuart Mathematical formula and write a book???

Mark