Here's something I'll strive to do with this blog every once in a while: provide you with suggestions for deep-sky observing. I'd like to suggest viewing some of my favorite objects, some of which are a little off-the-beaten-path. If you observe these objects, image them, or sketch them at the eyepiece, be sure to send us your material and we'll publish as much of it as we can in Astronomy or on our web page. Feel free to contact me at editor@astronomy.com.
Autumn deep-sky wonders
1. The Fornax Dwarf Galaxy and NGC 1049. Because its magnitude is 13.0 and its disk only 24" across, NGC 1049 appears as a pale spot of gray light in a 6-inch scope. When the seeing isn't terrifically steady, this cluster appears like an out-of-focus star or a small, colorless planetary nebula, although NGC 1049 is actually an enormous globular cluster located some 500,000 light-years away in a Local Group galaxy called the Fornax Dwarf Galaxy. Discovered at Harvard College Observatory in 1938, the Fornax dwarf is one of several tiny elliptical galaxies scattered throughout our Local Group. It is one of the smallest galaxies known, contains about 50 times as much mass as a typical Milky Way globular cluster, and measures only 6,000 light-years across. The Fornax dwarf has such a low surface brightness that it is beyond the reach of nearly all backyard telescopes. Yet, ironically, its brightest globular, NGC 1049, is readily visible in moderate-sized instruments.
2. Irregular galaxy IC 1613. Lying in the western part of Cetus is the large irregular galaxy IC 1613. This is a difficult object for small telescopes, as its integrated magnitude of 12.0 is spread over the large area of 11.0' by 9.0', resulting in a very low surface brightness. Under perfect skies, large binoculars or richest-field telescopes (RFTs) show IC 1613 as a dim, wispy glow — but under average conditions a 6-inch or 8-inch scope is the minimum needed to show the object. IC 1613 lies at nearly the same distance as the M31 group — 2.5 million light-years — comfortably earning its membership in the Local Group of galaxies, which extends out to at least 300 million light-years from the Milky Way.
3. M31's satellite galaxies NGC 147 and NGC 185. At the extreme southern end of Cassiopeia lie two galaxies that are also members of the Local Group. Located about 8° north of the Andromeda Galaxy, NGC 147 and NGC 185 are distant satellite galaxies orbiting the Andromeda spiral. Each is a dwarf elliptical galaxy, and although both are low-surface-brightness objects, each is visible with a 6-inch telescope under good conditions. NGC 147 shines at magnitude 9.3 and measures 12.9' by 8.1'. NGC 185 is a magnitude 9.2 galaxy spanning 11.5' by 9.8'. Both galaxies appear as ghostly patches of gray light in backyard telescopes.
4. Barred spiral NGC 6907 in Capricornus. The second brightest deep-sky object in Capricornus after globular cluster M30 is the 11th-magnitude galaxy NGC 6907. This barred spiral measures 3.4' by 3.0' and is bright enough to be viewed with a 6-inch telescope. A 10-incher shows it as a roundish patch with a bright middle, whereas large backyard telescopes reveal an evenly-illuminated, wispy halo of gray light around a bright oval nucleus.
5. Spiral galaxy NGC 976 in Aries. In north-central Aries some 2° southwest of the 5th-magnitude star Nu (ν) Arietis lies the small spiral galaxy NGC 976. This galaxy glows softly at magnitude 12.4 and measures 1.7' by 1.5'. It has a relatively low surface brightness, so it appears in a 6-inch scope like a small, nebulous patch without much detail.