Exploring the Milky Way

Exploring the Milky Way

(The August sky)

On warm summer nights far from the lights of the city, the sky is dominated by an awe inspiring band of light stretching across the sky – our own galaxy, which we call the Milky Way. The Milky Way reveals more detail to the casual observer than other galaxies do through the world’s most powerful telescopes – yet surprisingly few star atlases and observers’ handbooks devote more than a short amount of space to it. And no maps seem to exist that can give much help to the binocular user or astronomy enthusiast with a portable telescope. In short, the Milky Way has been ignored by observing books and charts. You’ll find however, if you take the time to look, that the Milky Way is an extremely rewarding subject for study with a very wide range of instruments – from your own dark adapted eyes, to binoculars, small telescopes, and richest field telescopes. It is an exhaustible source of objects foe viewing with even the largest telescopes.

The first thing you notice when you look carefully at the Milky Way is that it is by no means a simple object. It has variations in brightness, dark spots, bright spots, places where there are too many stars to count – and other places where there are no stars at all! We couldn’t expect it to be simple, of course; it’s a whole galaxy spread out before us, with all the detail and complexity, you’d find in a swarm of 100 billion stars.

Galaxy Rising. The obvious is sometimes false, the unexpected is sometimes true. We have come from the Cosmos and we were born ultimately of the stars and now for while inhabiting a world called Earth, we have begun our long voyage home.

When the Milky Way rises in the northern hemisphere it comes up almost parallel to the horizon. Cygnus and Cassiopeia rise first; then Aquila, Scutum and the claws of Scorpius, and finally the rich brilliant central regions of the galaxy in Sagittarius. By August, it’s high in the sky by the time darkness falls, and the southern parts in Scorpius and Sagittarius cross the meridian just after the end of twilight. By midnight the brilliant starclouds of Cygnus pass through the zenith. For campers, vacationers and city dwellers (perhaps getting a rare chance to be out of the city and under clear, dark country skies). August is the time to observe the Milky Way.

We’ll begin of the galaxy in the south, not because it’s brighter and contains more objects, but it is somehow fitting to start near the center of the galaxy. For the benefit of those living in the northern states, we’ll only go as far as 35 degrees declination.

For visual observers and binocular users, Sagittarius’ teapot forms a valuable starting point, much as the Big Dipper does for the north circumpolar stars. Looking south, the handle of the teapot (on the left) is composed of four stars, while the spout (on the right) contains three stars. Looking above the spout, you’ll see a puff of celestial “steam” about five degrees long. This is the richest and most brilliant starcloud in the Milky Way, known as the Great Sagittarius Starcloud. From northern latitudes it may not look as bright as some of the starclouds in Cygnus, but from latitudes where it passes overhead (and it isn’t dimmed by the atmosphere), it is brighter. Surrounding it are darker areas where the light from stars is absorbed by dust lying along the plane of the galaxy. The Great Sagittarius Starcloud shines through a “hole” in the dust. In fact, if the dust wasn’t there absorbing light, the entire Milky Way would shine more brightly than this starcloud does now.

If you use binoculars – or even just your eyes if they’re sharp – you’ll have already noticed the Lagoon nebula (M-8), located only a few degrees north of the starcloud. The Lagoon is a cluster of stars surrounded with a delicate glow of haziness – actually an H – II region where hydrogen fluoresces in the intense ultraviolet glare of the newly born star cluster in its center. Just a bit farther north, and quite a bit fainter, is the Trifid nebula (so called because it is divided into three parts) and a tiny open star cluster, M-21. But let’s not get carried away indicating specific sights: these fields are so rich that the slightest shake of bump of the telescope will bring new objects into the field.

Let’s start again from the spout of the teapot. This time let’s begin at the star where the spout joins the pot (Delta). Swing past the tip of the spout (Gamma) and about twice as far again; there, a bright open cluster (M-6) will be waiting for you. Nearby are four or five smaller and fainter clusters, easily seen in a small telescope or richest field telescope. Swing south and east a few degrees, and M-7, a really brilliant naked eye cluster, will dazzle you. In a big telescope, both M-6 and M-7 fill the whole field, as the Pleiades do in binoculars.

Where in the area is the exact galactic center located? In visible light there is nothing to mark it, although it can be “seen” in the radio and infrared that penetrate the galactic dust lying between us and the center: the spot is actually about two degrees west of the tip of the teapot’s spout. What a sight it would be if we could see it!

Another object that’s easy to find is the globular cluster M-22. The top of the teapot’s lid is marked by Lambda; a bit to the north and east you’ll find the globular. It’s a knot of about 100,000 stars, resolvable in a six inch telescope under good conditions; with binoculars is a fuzzy ball. M-22 is one of the biggest and brightest globulars in this part of the sky, but if you use a chart you can easily find many more including M-54, M-55, M-69, M-70 and M-28, along with lots of NGC objects.

Skipping over to Scorpius, let’s start at the obvious place – the red giant star Antares. Another globular cluster, M-4, found 1- ½ degrees to the west, is bright and easily resolved in a six inch scope. About midway between M-4 and Antares, and a bit to the north, is the much more difficult globular NGC – 6144. You shouldn’t have any trouble seeing it with a tree inch of larger aperture if sly conditions are good. North of Scorpius, spread through the dark expanses of Ophiuchus and Serpens, are quite a few globular clusters, including bright ones like M-5 and many smaller, fainter ones. But there we are getting farther from the Milky Way.

As you return from Scorpius toward the plane of the galaxy, you’ll notice a complex, patchy area far too complicated to describe accurately. This area of stars and starless patches is marked by dark nebulae of astounding complexity. Long dark lanes run from the area near Antares across about 15 degrees of sky into northern Sagittarius. This dust complex is not far from the Earth (as galactic distances go). It spreads along the inner edge of the sun’s spiral arm, seemingly stretched along the direction of galactic rotation. Whether it really does so or not, it certainly looks that way.

Just about 10 degrees north, along the galactic plane from the Great Sagittarius Starcloud , is the Lasser, or small, Sagittarius Starcloud. The open cluster M-24 is embedded in this cloud so that the cluster is hard to see against the starry background. On photographs, the Lesser Starcloud sometimes looks like a wide mouthed beast wearing dark glasses; hence it is also called the Google-eyed Monster (so much for nomenclature!). For degrees to the east is the brilliant open cluster M-25. Although it doesn’t have many stars, those it does contain are quite bright. Six degrees west is another open cluster, M-23. This much “smoother” cluster holds several hundred fairly bright stars. Direct your sight another degree north, and you’ll be looking at M-17, an open cluster bathed in nebulosity. This entire complex is called the Omega nebula. The nebula itself is a H-II region glowing primarily in the red light of hydrogen.

Another three degrees north is an open cluster with nebulosity: M-16, also known as the Eagle nebula. Both M-16 and M-17 are beautiful, softly glowing objects with sprinklings of stars in a six or eight inch telescope.

The fields we have crossed are filled with many more nebulae and clusters than mentioned. You can scan binoculars up and down this area and watch them go by. And it’s hardly possible to point a richest field telescope (or even a six inch at 40 power) at these areas of the Milky Way without having something interesting in the field.

When we look toward the center of the galaxy, lots of obscuring dust in our own spiral arm blocks the view in several places; but where that dust is thin, we can see right across a gap to the next spiral arm inward from ours. M-8, M-20, M-16 and M-17, for instance, all lie in that spiral arm (called the Sagittarius arm), while our sun lies in the Cygnus arm. As we look toward Cygnus (at right angles to the center of the galaxy), we’re looking down the length of our own arm at objects that generally lie closer to us. Just a quick visual scan of the Milky Way in Sagittarius compared to the Cygnus section will convince you that something is rather dramatically different. Where Sagittarius is complex, Cygnus is simple; where Sagittarius is full of incredible numbers of very faint stars, Cygnus has many more bright stars, and generally a smoother appearance.

The overwhelming naked eye feature that extends all the way from Scutum and Serpens Cauda up to Deneb in Cygnus is the Great Rift. Lying very close to the galactic plane, the rift is a huge lane of dust of dust obscuring everything lying beyond it. We see this remarkable dark cloud of dust against the starclouds of the galaxy that silhouette it on either side. Its length is nearly 1/6 of a full circle, spanning 60 degrees of sky. But in spite of its darkness, the Great Rift is brighter than the sky well away from the band of the Milky Way – an effect due mainly to the rich layer of stars between us and this dust band.

Near the southern end of the Rift, cloth to the galactic plane, is a starcloud called the “gem of the Milky Way” by E.E. Barnard, pioneering photographer of the Milky Way. The Scutum Starcloud is brilliant, though not as bright as the Great Sagittarius Starcloud. But northern observers have a better view of it because it is higher in their sky. Tucked away along the starcloud’s northern edge is the impressively dense open cluster, M-11. Small telescopes can barely resolve this cluster, but a six or eight inch reveals hundreds upon hundreds of stars crowded into a tight little ball. On the southern edge of the Scutum Starcloud nestles another small cluster, M-26. It isn’t nearly as rich as M-11, but is still an easy mark for binoculars.

Moving north across the Great Rift, you’ll find several more large clusters in Aquila and Serpens embedded in a branch of the Milky Way that pushes out into the dark expanse of Ophiuchus. NGC-4756 and NGC-6709 are both easy to spot in a small telescope; the former sprawls across a full degree of sky.

As you follow the Great Rift north toward Cygnus, you’ll pass some dense dark nebulae when you reach the declination of Altair, the bright star in Aquila. Dark nebulae, however, are hard to see; even the slightest bit of moonlight or nearby town-light will blow them out. The Rift may have a side branch here because the western lobe of the Milky Way is missing entirely in Vulpecula, presumably obscured by the omnipresent dustlanes that lie along this stellar band.

But as we enter the constellation Cygnus, we encounter a stunning revival: the Cygnus Starcloud, a rich oval nearly 20 degrees long and six degrees wide. Here is one of the most fabulous fields in the sky for an RFT, this cloud can only be called mind boggling. The various over-layers of brilliant young blue stars are stellar associations – young star groups recently born and shining brilliantly against the deeper, uniform background of faint stars too numerous to count. On color photographs of this area, you can easily see this concentration of hot blue stars. Toward the northern end of the star-cloud, near Gamma Cygni, you may also detect faint wisps of nebulosity.

Hop over the Rift to the less spectacular eastern branch a bit south of Epsilon Cygni, and find the star 52 Cygni. Careful scrutiny of this field with a six inch telescope scope reveals the western arc of the Cygnus loop nebula. This supernova remnant is a faint wisp of nebula a degree long. More care is needed to see the other half of this loop of gas because there’s no guide star. A few degrees south, you can see NGC-6940 – a small oval cluster of stars.

The main thrust of the Great Rift it toward the Deneb, but it turns suddenly to the west, and a starry region lies in your path. The North America nebula (NGC-7000) lies in the region. The nebula itself is very hard to separate from the rich stellar under-layer which follows the same outlines. In an RFT you can certainly spot the nebula if the sky is clear and very dark, and many people can see the nebula in large binoculars. With your eye, you’ll see the stellar background, but probably not the nebula itself. A few degrees farther long the Milky Way in the cluster M-39, composed of a very few bright stars. It’s a good sight in binoculars, but is lost in most telescopic views of the area.

With M-39, we’ll end our tour of the summer Milky Way. Have we omitted any objects? Absolutely! The fields are so rich, and so many smaller, dimmer, and more subtle structures of dust, gas and stars lie waiting to be seen that the job can never be finished. Come back for another look – for many more looks – and don’t forget to bring your camera next time!

Binoculars will bring you close to the Milky Way, but without color. Human eyes are insensitive to color at the faint light levels typical of Milky Way objects –such as this view of M-8 (the Lagoon nebula) and parts of the nearby Sagittarius Starcloud. Visually, the nebula has a slight tinge of green, the brighter stars gleam with a touch of bluish color, and the star-clouds with a colorless pale glimmer.

(By Richard Berry, Astronomy)

The artist can render best the visual appearance of the Milky Way shown here stretching from Sagittarius to through Cepheus, encircling 1/3 of the sky. The combination of delicacy and detail, seen by the eye from a site of superb quality, is never captured on film. The key locates some of the major features that you can easily see by eye or with slight optical aid.  One of the richest parts of the Milky Way stretches from the tip of Scorpius’ tail to Scutum. M-6, M-8, M-20, M-16 and M-17 lie very close to the galactic plane, almost defining it. The Small Sagittarius Starcloud shows a “monastery” aspect in shades of delicate blue – the result of young hot stars in it. Note that along the galactic plane, dense obscuring dustclouds block our view of the galactic core. Galaxy Rising. Artwork by Adolf Schaller. Source of the image : omnicosm.com