Big, Bright & Beautiful in October
By Max Gardner AM
The meridian at 10 pm in October has fewer objects than most months, but does boast the largest bright planetary nebula and one of the finest globular clusters. This month we can really take our time and study the field at leisure, so let us get out under the stars and look around. Don't forget to give your eyes up to half an hour to dark-adapt before seeking out the fainter objects.
As the northern section of the meridian is very short of bright objects, we might steal a march on next month and look a little to the east of the north point. Here, in the constellation of Andromeda, about fifteen degrees above the horison, and plainly visible to the naked eye as a softly glowing patch, lies on the third brightest galaxy in the sky - the mighty Andromeda Galaxy or M31. It is so big that it looks best in lowest power in almost any scope. In fact, I prefer the view of it through binoculars, which show the enormous extent of the galaxy, with its massive central core, extensive disk and the dark dust lane. On a really good night you might even spot a dark lane on either side of the core. More power will show areas of bright knotting and nebulosity at either end of the disk. Remember, we are looking at a galaxy even larger than our Milky Way, and over two million light years distant! Notice also the two small companion galaxies. The one on the northern side is M110, with the other, M32, closer to the core and on the other side of the disk. Quite a remarkable sight.
At about the same elevation above the horison, still in Andromeda but back almost on the meridian, we find NGC 7662 an 8th magnitude planetary nebula. This has a distinctly blue disk and revels in the name "The Blue Snowball". More power will show some softness of the edge of the disk, even a faint ring further out from the disk. If you ever attend a star party in the U.S.A, you can expect to be shown M31 and the Blue Snowball pretty often - they are amongst the northern hemisphere's most popular objects.
Moving up the sky (south) we cross the broad expanse of the constellation of Pegasus, which has many galaxies but few bright enough for our purposes. However, just three degrees due south of the 2nd magnitude star Alpha Pegasus lies NGC 7479, an 11th magnitude spiral galaxy. It is only of interest to larger apertures, but my observing notes say: "It has a long slim disk with a long oval bar. At the south end, the disk curves back into a ring around the whole galaxy. An interesting shape."
Further south, we enter the constellation of Aquarius. Almost on the southern border we encounter what is unquestionably the largest planetary nebula accessible to most amateur scopes - the mighty "Helix Nebula", or NGC 7293. Its visual magnitude is quoted as 7.3, but this is somewhat misleading as it appears much fainter, being a very large object indeed. Smaller scopes may be hard pressed to spot it, but persevere as it is very rewarding. Its approximate position is at the western apex of an almost equilateral triangle based on the stars Delta Aquarii and Fomalhaut (Alpha Piscis Austrinis) The Helix is named for the stunning annular ring-shape of the body. The inner areas of the ring glow very faintly and show several stars to larger apertures. One of these is the 13th magnitude progenitor of the nebula, or the "central star". Larger scopes will show wonderfully delicate spiral structure in the ring, with much variation in brightness. An O-111 filter will enhance the contrast and show even greater detail. Truly the Helix is an exciting object to find.
Almost at the zenith is the western end of the constellation of Sculptor, which has a feast of fine galaxies waiting for us next month. For tonight we shall seek only one target, the large but rather dim 9th magnitude galaxy NGC 7793 which lies in an area of sky devoid of prominent stars. It is not plotted in Sky Atlas 2000, but appears in the Herald Bobroff Astroatlas. My notes of this object say: "A huge, low brightness, face-on spiral. It is an M33-type galaxy with a large but faint core. Spiral arms and other structure are faint but clear." Definitely one for larger apertures, but give it a try.
Past the zenith we move south into the prominent constellation of Grus with it's unmistakable flying fish shape. Grus is a storehouse of galaxies and a very happy hunting ground for larger apertures. Smaller scopes will find many faint fuzzies grouped together in interesting collections, but most are too faint for this article. However, the spectacular "Trio in Grus" are worth tracking down. Comprising three quite bright, elongated galaxies, NGC 7582, NGC 7590 and NGC 75999 close enough for all to be within a single eyepiece field, this is one of the high points in this constellation. The Trio can be found close to the belly of the fish, almost on the border with the constellation of Phoenix. My observing notes of these galaxies say: "7582 is very elongated with a long, slender disk, large bulge and a round core. Dust, knots and structure can be seen along the disk. 7590 is elongated with a small bar and obvious mottling and structure in a thick disk, which is brighter on the west end, closest to 7582. There is a bright star on the other end of the disk. 7599 is an excellent elongated galaxy. It has a thick irregular disk with small, dim bar, offset to the north-west. There is structure throughout, especially on the north-east end, but no core is visible. A star appears on the north edge of the disk".
Our final object for tonight is further south and east in the constellation of Tucana. It is located just on the western side of the small hazy patch which is The Smaller Magellanic Cloud (SMC). Easily visible to the naked eye at almost 4th magnitude, this object was originally mistaken for a star and given the stellar designation 47 Tuc. Now, often known by that name, it is recognised as the superb globular cluster NGC 104. A wonderful sight in any scope, to my mind it provides the greatest spectacle of all the globulars. It resolves into tens of thousands of tiny stars that form a wonderfully wide, almost circular edge. As you move to the centre, the star density increases sharply, eventually compressing and forming a surprisingly small, but still resolved core. Often there appear to be fine dark lanes running through the disk, but this is almost certainly a contrast effect from patterns of bright stars against the fainter background stars. Many of the stars show orange and yellowish hues, making the whole object seem alive with colour, which is most unusual with globular clusters. You would have to be a pretty jaded observer not to get an enormous lift from seeing this magnificent object.
Next month we shall explore the treasures of the SMC. See you then.
H.B. = Herald Bobroff Atlas Chart No.
SA 2000 = Sky Atlas 2000.0 Chart No.
Mag = Visual Magnitude (Brightness)
Dia = Apparent Diameter (arc mins)