Sunday, May 22, 2016
Issue #494, The Messier VII: The Greatest
Before we get to the Great Nebula, let’s talk about “how.” We’ve talked about why novices (or anybody else) might want to take on the Messier list, and we’ve talked about “what,” as in what sort of telescope to use on these deep sky wonders. Now we will address “how” as in “How do you look at ‘em?” What are some tricks and tips for seeing as much of these legendary objects as possible?
The most important thing you can do to improve the appearance of the Messiers, the galaxies and nebulae especially? Naturally, “Get thee to a dark site.” But what if you don’t have a dark site? Or want to observe more often than on once or twice a month runs at a club dark observing location? You can to some extent darken your backyard sky.
The easiest way to do that is with a trick many novices—and more than a few old hands—don’t know: increase magnification. The problem with seeing dimmer objects from the backyard is one of contrast. There is too little contrast between Messier object and the sky background in the eyepiece. The sky is nearly as bright—or as bright—as the M, and the deep sky object is rendered invisible or nearly so.
How do you fix that? Bump up the magnification. Increasing power spreads out the background skyglow, making it less intense. It will also dim the Messier, but often it still provides increased contrast and improves the view. Sometimes a lot. Experiment with a variety of magnifications on each object, but what you want is a power that dims the background but still leaves sufficient space around the object. If you kick up the power so much that the DSO fills the field, there will, again, be a lack of contrast. There will not be enough dark sky around the object to provide contrast.
Another way to darken the sky is to use Light Pollution Reduction (LPR) filters. I have an in-depth article on the subject of deep sky filters coming up in the August issue of Sky & Telescope, so I will refer you to that. Here, I’ll just say filters can make the difference between seeing and not seeing dimmer nebulae.
The next two tips have to do with physiology of the human eye and brain. The most important of the two is called “averted vision.” You’ll find that when you look off to the side of a faint object, look away from it instead of directly at it, you see dimmer features. That’s because looking off to the side of an object brings the eye’s dim light receptors, the rods, which are located around the retina’s periphery, into play.
At first it may feel odd or awkward to look away from the quarry instead of directly at it, but with a little practice you’ll get used to that. Under some circumstances, averted vision may allow you to see two or even more magnitudes dimmer than looking straight at the target and employing only the eye’s cones, the bright-light color receptors.
Jiggling the scope won’t give as much of a gain as averted vision, but it will still yield some improvement. The human eye-brain has an easier time seeing moving objects than stationary ones. That is probably evolution at work. Being able to see moving objects well—like a stalking leopard—would be a survival mechanism. So, tap the scope tube lightly, introducing some vibration, and you may be able to bring home details that were formerly invisible.
What can improve the performance of your eyes even more, perhaps, than the two previous techniques? Allowing them to become as dark adapted as possible, allowing your eyes’ irises to open up as much as possible. Yes, the sky is bright from the backyard, but if your eyes could obtain some dark adaptation, you would see more. What prevents that isn’t really the bright sky so much as it is ambient light, light from nearby sources. Your porch light, the neighbor’s yard light, etc.
What you want to do is rig up some means of shielding yourself and your telescope from intrusive ambient lights you can’t shut off. You can build light shields to shade the scope—I used to construct muslin covered stage flats for that purpose—or you can go simpler and more portable with a sheet of black cloth. A square of black nylon draped over your head can work wonders. What do you do to retain your night vision when you aren’t at the eyepiece? You could try Orion’s silly-looking red-tinted goggles, but cheaper and perhaps more effective might be an eye-patch from the drug store.
Finally, keep that bad ambient light out of the telescope. Most refractors and catadioptric telescopes have dew shields sufficient to keep ambient light out of the optical system. Newtonians are another matter. Modern fast Newts typically don’t have much tube ahead of the secondary mirror, so rig up a tube extension of black material of some kind—plastic, cardboard, whatever—to keep stray light off the secondary mirror.
Check the rear of a reflector, too. The primary cell may have some openings—a good thing where cool down is concerned—which can admit light reflected up from the ground. Rig up a cardboard baffle you can tape or Velcro over the rear of the tube to keep ambient light out of that end of the OTA when cool down is done.
With this arsenal of observing hints and kinks in hand, let’s tackle the next group…
M42 The Great Nebula
And great it most assuredly is. Along with the top globular star clusters of summer, M13 and M5, this is probably the greatest, most spectacular Messier of them all. This HII region, this emission nebula, shines with an integrated magnitude of 4.0, so, despite a size of at least 1-degree 30’ x 1-degree, it is seriously bright. It is, in fact, easily visible naked eye even in the city as the slightly fuzzy middle star in Orion’s sword.
Finding? Since it's a naked eye object, once you know what that fuzzy star represents you’ve found it. As I discovered when I was a little bitty kid with a 4-inch Palomar Junior Newtonian. I was hoping to get a copy of Norton’s Star Atlas “soon” so I could begin seeing deep sky wonders, but to my delight one cold December night, I found star charts are not needed for all Ms. I got curious about that funny star in Orion’s sword, pointed my little telescope to it, and there—OHMYGOD—was the Orion Nebula in my 1-inch war surplus optics Kellner eyepiece.
I won’t reiterate the descriptions of M42 found in a thousand books. I’ll just point out a couple of particulars I don’t hear much about. Yes, the nebulosity is great. Yes, there’s the Trapezium and the other fascinating stars enwrapped in that nebulosity. But what I tend to look at/for more than those things these days are the dust lanes and the nebula’s color.
Up the magnification and start exploring the area of the “fish’s mouth,” the dark bay in the nebula near M43, the companion nebula. This area is criss-crossed by many brownish (in images, anyway), dusty tendrils, and tracing them out in the eyepiece can be a fascinating pastime.
Color? Oh, yeah, I know the party line, “M42 may occasionally appear faintly green in medium aperture telescopes, and large aperture reflectors can sometimes show brown tinges that represent the nebula’s pinks and reds.” That’s true under normal circumstances, but on special nights, and I am not quite sure exactly what makes some nights special, M42 can literally appear stoplight green. Not faint green, but bright green. In an 8-inch or even smaller telescope.
How about trying Light Pollution Reduction filters on M42? I never use them much on Orion. Even in light polluted backyards it holds up well thanks to its brightness, and I prefer its look without an OIII or UHC filter. One of those may be of use when you are seeking fainter details, however. Start with the UHC.
M43, M42’s little buddy, is a smaller comma-shaped patch of nebulosity surrounding the magnitude 6.75 variable star Nu Orionis. M43 subtends 20.0’ x 15.0’ and glows at magnitude 9.0 (that’s the value usually given, but the central area is brighter than that). Not only is M43 interesting in and of itself; it’s a good indicator of the quality of your sky. If you can make out the comma shape easily in a medium aperture scope, you’ve got a good night ahead of you.
What’s to see here, about 10.0’ northeast of the main Orion Nebula? Quite a bit beyond the nebula’s basic shape. Under good skies with a magnification of 250-300x, there are plenty of details available. This, as above, is the area of dusty clouds, and you’ll see them encroaching on the south-southeastern edge of the nebula. You’ll also see the comma’s edges are wispy and complex and deserving of considerable attention. Like the main nebula, I’ve never thought that an LPR filter of any type improved the appearance of M43.
Ah, yes, the good, old Beehive, one of two Messier open star clusters in Cancer. M44, AKA “Praesepe” (“manger”), is a bright one, glowing with a combined magnitude of 3.10. Alas, it is also a large one, extending 1-degree 10’. That makes it proper fodder for big binoculars or a richest field telescope, not something like an f/10 C8. You need considerably more than 1-degree of field to make this one look good, you need a couple of degrees in order to put some empty space around the cluster’s stars.
If you can see the dim constellation Cancer the Crab, you are in like Flynn when it comes to finding. M44 lies in the middle of the triangle formed by Eta, Gamma, and Delta Cancri. If these stars are difficult to make out, it’s still easy enough to locate the target. Just point the telescope in the general area where the center of Cancer is or should be, and your 50mm finder should reveal the cluster without a fuss. In fact, it’s easy to see naked eye from medium dark sites on transparent evenings. In the olden days, people gauged the weather by the appearance of the Beehive. If it was easy to see, nice days were ahead. If not, storms were coming.
When you are on the correct spot, a 6 – 8-inch RFT will show a loose group of about 40 – 50 suns arranged in a slightly oval shape. 70 – 80mm binoculars will real maybe half that number. To me, M44 always looks slightly yellowish, which is understandable given the group’s fairly advanced age (for a galactic cluster). It is rife with red giants.
Don’t put that RFT or binoculars away. The next one is another big one, M45, the famous Pleiades, the Seven Sisters, the daughters of Atlas. Just about everybody has seen this huge (1-degree 50’) and bright (magnitude 1.2) galactic (open) cluster. Almost all my freshman astronomy students know it, though they usually think what they’ve seen is the Little Dipper thanks to the group’s brighter members forming a slightly squished dipper asterism.
Since you won’t have to hunt M45, you can give this group plenty of telescope time. In my old StarBlast RFT or my even older Short Tube 80 refractor, the Pleiads were simply stunning. Even an 80mm telescope brings in hordes of dimmer suns in addition to the bright sapphires that are visible naked eye. There’s something to be seen here in addition to cluster stars as well: reflection nebulosity.
The nebulosity, which is brightest around the cluster star Merope, thus giving it its name, “The Merope Nebula,” is extensive, but it is also dim in the way only reflection nebulosity can be. It’s easy to image, as in my picture above, taken with an 80mm APO last autumn, but seeing traces of it visually requires a dark site and good transparency. Even then, it’s hard to be sure whether you’re seeing the nebulosity or not. The time-honored analogy is “baby’s breath on a mirror” and that is true in spades. By the way, the Merope Nebula does not represent the remains of the cloud that formed the star cluster; it’s just an area of dust and gas the group is currently moving through.
Y’all know I love bonus objects, deep sky objects with another deep sky object close at hand. In this case, really close at hand. M46 is a nice enough open cluster, mind you. 50+ stars are visible in an 8-inch as a rich group 20.0’ across shining with a combined magnitude of 6.10. On the other hand, the cluster is in an obscure constellation (for novices), Puppis, and is a smidge low for more northerly observers at a declination of -14. There’s that bonus, though, and that makes M46 over the top wonderful.
First you have to find M46. As always, the most efficacious method is just to punch in M-0-4-6 on the hand control. Can’t do that? It forms a long triangle with Eta Monocerotis and Sirius, and you really won’t need much more guidance than that. Under slightly putrid skies it still shows up as a smudge in a 50mm finder. Just don’t confuse it with M47, which is only 1-degree 20’ to the northwest. If the cluster in the eyepiece has a wide range of star brightnesses, with a couple of really prominent ones, you are on M47, not M46.
The cluster itself is a nice one, a basically round and rich group that can show as many as a hundred stars to a 12-inch telescope. There’s a small range in star brightness, most of them being of magnitudes 7 – 9, and that gives the group a substantial, solid looking form; it is well detached from the background. It’s little NGC 2438 that is the prize here, however.
NGC 2438 is a small, 1’10” planetary nebula that looks like a perfect miniature of the big ring, M57. While it’s somewhat dim at magnitude 11.7, the small diameter keeps it easy for small aperture telescopes. I’ve been able to prise it out with an 80mm refractor at 150x. If you’re having trouble finding it, keep your eye peeled for a "funny-looking" double star 5’ north of the cluster's center. The double looks funny because the planetary nebula is involved with it.
M47 is good, fine, alright, but to tell you the truth, I’d seldom look at it if it weren’t for nearby M46. It’s an OK, cluster, but just OK. Because of the large brightness range of its stars—there are several magnitude 4 – 5 suns in the field—it just doesn’t look as nice to me as M46. The brightness range makes it appear sparser than it actually is, and it is less rich than M47 to begin with.
If you can locate M46, you can locate M47. In your 50mm finder, it will be the cluster to the northwest, and will look brighter given its magnitude of 4.40 coupled with a modest size of 25.0’. Still not sure? It is the group that appears more resolved in a 50mm finder.
When you are on M47, you’ll note it’s basically shapeless, but that the bright stars at its center form a dipper shaped asterism, sort of like a miniature Pleiades or an M39. The view is similar in 8 to 12-inch telescopes, with about 30 dimmer stars being visible in addition to a dozen or so brighter members.
Hydra’s M48 is similar to M46 in that its stars have a fairly narrow range of brightness. It is somewhat brighter than M46, with an integrated magnitude of 5.8, but is not nearly as rich in my 8-inch. Still, not bad, not bad at all. What most novices will find challenging about this one is not looking at it but looking for it.
If you don’t have goto or digital setting circles, the best bet is to use a half degree long line of three stars aligned northwest/southeast as a signpost. 1 Hydrae, C Hydrae, and 2 Hydrae are located 4-degrees 15’ northeast of Zeta Monocerotis, are in the magnitude 4.5 – 5.5 range, and stand out well in a finderscope. M48 is 3-degrees 15’ northwest of the three stars and should show up without a hassle in a 50mm finder.
In the eyepiece, you’ll see a scattered, strongly elongated group of about 30 stars. It would be pretty ho-hum if not for the line of bright(er) members that crosses the center of the group. That line of stars, and a couple of arcs of suns also involved in the cluster at least make it somewhat interesting.
Now for something entirely different to end on, a Virgo galaxy, M49. It is bright and impressive for a galaxy, having a magnitude of 8.3 and a size of 10.0’, just right to be easily scarfed up by a 4-inch or even smaller telescope. No, there’s not a lot of detail to be seen, but it is a galaxy that is easy to run down from the backyard. The only problem is how to run it down.
M49 lies in the galaxy-rich wonderland, the “Realm of the Nebulae” between the arms of Virgo. The only saving grace here is that it lies well to the south of the densest area. There are numerous NGCs nearby but no adjacent bright Messier galaxies to confuse you. Still, it’s not easy the first time you undertake to navigate the Virgo Cluster with finder scope and chart. What I used to do before computers was “galaxy hop.” I’d use a wide-field Erfle or, later, a Nagler eyepiece, begin at the Star Vindemiatrix, and literally hop from one galaxy to the next, using them as steppingstones to my destination.
When you are finally there, however you get there, don’t be too disappointed. What will be in the field is something that looks a lot like an unresolved globular cluster. A bright core and a hazy, round outer envelope. The better the sky, the bigger the envelope. This is a Hubble Type E2 galaxy, an elliptical galaxy, so there is simply not much detail beyond that to be seen. There are some nearby small 13th magnitude galaxies that can be visible in 12-inch and larger telescopes, and there are a couple of magnitude 13 range stars close by—nope, sorry, you have not discovered a supernova—but that is it.
And here we are approaching the halfway point in the list already. That is reason enough to put on the brakes. These objects are made to be savored. I won’t dash through them when writing about them, and you shouldn’t dash through them when viewing them, especially for the first time.
For me works бест - Observing Hood. That is Google search https://www.google.ru/search?q=observing+hood&newwindow=1&client=safari&rls=en&biw=1280&bih=659&source=lnms&sa=X&ved=0ahUKEwi0nNTgmu7MAhXqFZoKHbEyDgIQ_AUIBigA&dpr=2#newwindow=1&q=The+Observing+Hood+(%E2%80%9CMonk%E2%80%9D+hood+style)
The hood allows you to see much more without increasing the aperture of the telescope.
The hood allows you to see much more without increasing the aperture of the telescope.
Phyllis kindly sent me a copy of DSP 7, and I'll be doing a review of it sometime in the next several week. But it looks great thus far.Post a Comment