Observing Nebulae Season by Season
Many fine nebulae are visible even in small telescopes.
Deep-Sky Wonders, a month-by-month selection of those columns, was published in 1999 and is available from Sky Publishing. The following seasonal guide to a variety of nebulae consists of excerpts from the book.
The Beauty of Orion
The Orion Nebula (M42) has inspired more adjectives than any other deep-sky object. None, however, do real justice to this great mass of swirling, pale green, chaotic gas. Even “overpowering” is a most inadequate word when the nebula is seen in a really dark sky. Intertwined with the Sword on the Hunter’s Belt, M42 requires no charts or setting circles (see the photograph on the previous page). There’s no need for a finder, either, since you can simply sight along the edge of the telescope tube to bring the nebula into view. (For more on the Orion Nebula see the article "A Pair of Nice Nebulae.")
But recognizing the dark blotch B33 is another matter. Scattered light from 2nd-magnitude Zeta foils many attempts to find the Horsehead, since the two are separated by only ½°. Another reason that many searches fail is that observers are looking for the wrong-sized object. When I have seen it with telescopes between 10 and 16 inches in aperture, my first reaction has always been how tiny it is! Knowing just where to look for it is half the battle. The Horsehead is only 5' across. Amateurs accustomed to seeing it on large-scale photographs end up looking for an object that is much too big.
The Crab Nebula and Other Winter Treats
One object that everyone should enjoy is M76, an unusual planetary nebula on the edge of a dense part of the Milky Way. Often called the Little Dumbbell because it resembles the more-familiar Dumbbell Nebula (M27), to me it always looks more like a dog biscuit. The nebula has a reputation of being hard to find, so here's how best to find it. Start with Phi (φ) Persei. This star and a dimmer one just to the south form a pointer, with Phi at the head, that directs the observer to a diamond of faint stars, within which M76 is dimly perceptible.
With a small aperture or in indifferent sky conditions, M76 shows only a dim irregular oval with ragged edges. But one night, with an 8-inch reflector in the hills north of the Golden Gate in San Francisco, M76 was a most exciting object. High magnifications brought out an intricate network of turbulent celestial clouds.
A Spring Rosette and the Ghost of Jupiter
The Rosette is one of the few deep-sky objects better seen with a telescope's finder than with the main instrument. With large binoculars and good observing conditions, the Rosette may appear as a formless aura of soft light encircling a cluster. But equipped with a proper filter, just about any telescope will show it.
There is a fine planetary nebula in Hydra, NGC 3242. It is located about 2° south and slightly west of the 4th-magnitude star Mu (μ) Hydrae. It's sometimes called the Ghost of Jupiter because it's similar in size and color to the planet Jupiter. The total light of NGC 3242 roughly equals that of an 8th-magnitude star. With a disk only 0.5' in diameter, the surface brightness of this planetary is quite high, averaging about 10 times greater than the Ring Nebula in Lyra. I looked at it with my 5-inch Apogee telescope and a 20x eyepiece. It appeared slightly oval but without the pointed ends so prominent in photographs of the object. I also examined NGC 3242 with a Lumicon UHC nebula filter. The results were impressive.
Two Great Summer Planetaries
I have probably looked at the Ring Nebula with a greater variety of telescopes than I have at any other heavenly subject. One of my best views came with the 12-inch f/17 Porter turret telescope on Breezy Hill in Springfield, Vermont, the site of the annual Stellafane convention. At 200x the ring was bright, slightly elongated, and of uniform luminosity. An increase to 600x changed the picture dramatically. No longer was the smoke ring evenly bright. Instead, two sides of the ring were made up of curved and twisted streamers. The oval now had pointed ends, and the central region was full of turbulent detail.
I don't believe many observers see the dumbbell shape without having a bad wrench to the imagination. With my 4-inch Clark refractor, a quick look reveals the planetary as two cones with their apexes in contact. After finding the best eyepiece for the evening's sky conditions, and by using averted vision, I usually see the faint nebulosity between the brighter parts of the cones. By gently rocking the telescope back and forth which sets the planetary in motion and helps the eye capture the faintest extensions of light I found the end result is a full circle of light, just as one would expect of a planetary. The luminosity of the interior varies greatly, but the circular outline remains firmly fixed. (For more about the Dumbbell Nebula, see "A Pair of Nice Nebulae.")
More Summer Sights
Close to the southern edge of the Big Dipper's Bowl is the remarkable planetary nebula M97, popularly known as the Owl. M97 is no problem for 4-inch telescopes, and I have easily seen it in 15 x 65 binoculars. The two dark spots that form the Owl's "eyes" are more challenging, but under good skies they might be within range of a 4-inch telescope. The nebula measures only 3', and if it isn't seen at once, let your eye wander aimlessly over the field of view until the disk springs into view.
In Ophiuchus is the globular cluster M9. It's near the northeast edge of a remarkable dark nebula, Barnard 64, less than ½° west of it. With my 4-inch Clark refractor or 5-inch Apogee telescope the dark nebula is easily seen. Most dark nebulae are difficult to "see," but here the rich background is rather uniform, and it's interesting to compare the star densities northeast and southeast of M9. Try powers of about 100x. (To discover more dark nebulae, see the article "Seeking Summer's Dark Nebulae.")
Three Challenging Autumn Nebulae
Actually, NGC 7000 is difficult to see in most telescopes. With a 5-inch Moonwatch Apogee telescope you should know beforehand what it looks like, and the nebula is downright challenging in a 6-inch f/4. However, a few years ago it was brilliant when I saw it in an 11.4-inch Wright telescope.
The most famous celestial sights have been passed down to us throughout the centuries. There are some objects which, in a sense, belong to the modern amateur. One such object is the Veil Nebula in Cygnus, a broken bubble of luminous gas some 2° in diameter. Although ignored by generations of telescope users, in the last 30 years the Veil has progressed from a difficult test object to a reasonable target for anything from binoculars to the largest amateur telescopes. It's an excellent nebula for training the eye, perhaps the most important observing "accessory," to help us get the most out of the telescope we're using.
Both the east and west arms of this loop are easy in my 20 x 125 Japanese military binoculars. In a 12-inch f/5 telescope the Veil Nebula in Cygnus is beautiful, and so bright that one notes it even when sweeping. But in a 5-inch f/5 the Veil is visible only with difficulty to keen eyes.
The planetary nebula NGC 7293, also known as the Helix Nebula lies in Aquarius about a third of the way from Upsilon (υ) Aquarii to 47. It has a total magnitude of about 6, but its large apparent diameter nearly half that of the Moon spreads the light out and makes it a difficult object visually. I recently saw the Helix Nebula with the 4-inch Clark refractor and was certain that it was glimpsed in a 2-inch finder. Years ago I suggested that readers send me their observations of the Helix Nebula. The bulk of my correspondents indicated that the Helix was more readily seen in binoculars and finders than in telescopes.