Caroline Herschel Objects

By Jane Houston Jones

from Nov 2002. Sky & Telescope Magazine, p. 107.

Twelve deep-sky sights make up the "other" Herschel catalog. Most are in view this season. Can you log them all?

WHEN I GAZE AT CANIS MAJOR sparkling on a cold night I sometimes time-travel back to 1783. I picture Caroline Herschel, age 33, at her small telescope near Windsor, England. The Sun has set, her older brother, William Herschel, is out of town, and she is about to make a discovery that now bears her name.

Two years earlier William had become famous by discovering Uranus. On quiet nights when he was away, Caroline swept the sky with her small reflector for discoveries of her own, particularly comets. Caroline did not have much free time. When William was at the eyepiece of his 20-foot-long reflector she was always there with pen and ledger, recording his observations of faint deep-sky objects. On cold winter nights the ink sometimes froze in her inkbottle. William kept his telescope aimed at the meridian; Caroline noted the elevation of each object he sighted and the sidereal time, as well as his spoken comments, and the next day she reduced the many readings into right ascensions and declinations. Then she would plan the next night's observing schedule. Nearly 2,500 of these "Herschel objects" would form the core, a century later, of the NGC, the New General Catalogue of Nebulae and Clusters of Stars.

"Do you know how to find Caroline's Cluster?" a friend asked me at a club star party on Mount Tamalpais near San Francisco early this year. Her coincidental question jolted me out of my 18th-century reverie. After collecting my thoughts, I obliged her by aiming my 12.5-inch f/5.75 reflector in the direction of Caroline's Cluster, NGC 2360 in Canis Major, the lovely object that Caroline discovered with her telescope that night in 1783.

In addition to hunting comets (she eventually discovered eight), Caroline Herschel cataloged 13 deep-sky objects of her own while not working for her brother. Four are in Cassiopeia, and two each are in Andromeda and Canis Major. Cepheus, Sculptor, Hydra, and Ophiuchus each hold one "C. Herschel" object. And a mystery object in Monoceros has never been identified.

Caroline Herschel taking notes as her brother William observes. This engraving by P. Fouché was meant to illustrate the pair on March 13, 1781, the night William discovered Uranus.

Unlike most other Herschel objects, hers are generally bright and easy. Many amateurs are familiar with the selected "Herschel 400" list; the Astronomical League grants its Herschel Award to observers who log all 400, a worthy goal for amateurs who have recorded the 110 or so Messier objects (see www.astroleague .org/al!obsclubs/herschel/hers400.html). The Caroline Herschels form a small and interesting subset of the Herschel 400. Why not plan to observe them this year? Rather than just ticking off these objects on a checklist, I hope you will stop and contemplate them for a while. Imagine the thrill of discovery Caroline must have felt on those long-ago nights.

Ten of the objects make good fall targets for Northern Hemisphere observers. Save two of them for spring and summer stargazes. And tackle the remaining mystery object in the armchair some rainy night.

NGC 7789 in Cassiopeia is a beautiful and well- known open cluster, a rich swarm with, however, no stars brighter than 11th magnitude. Compared to many clusters it's delicate and lacelike. I observed it several times before someone told me its modern nickname, the Magnificent Cluster. I first logged it and the other three C. Herschels in Cassiopeia on November 2, 1997, with Strider, my brand-new 12.5-inch Litebox Dobsonian reflector made by Barry Peckham in Hawaii. I like to observe clusters with a variety of eyepieces, and each view from 83x to 200x was different. The lower power yields more than 100 stars, with some pretty star chains and many dark lanes. At 200x there's a small, dark, starless spot in the middle.

NGC 7789 is easy to find 3° southeast of Beta Cassiopeiae, the easternmost star of Cassiopeia's W pattern. Caroline discovered it in the fall of 1783, and it is cataloged in the William Herschel list as H VI-30, the 30th object in his Classification VI: "very compressed and rich clusters of stars?"

NGC 225 is a loose cluster that looks great in every telescope. It's a cinch to locate halfway between Gamma and Kappa Cas. To me it looks like a triangle of triangles, with one little trail of stars dividing them. About 30 stars show in my 12.5-inch. Caroline discovered this object in 1784, and it became the 78th object in Herschel's Classification VIII: "coarsely scattered clusters of stars?"

NGC 381 is a fainter and smaller open cluster located just 1.6° northeast of Gamma Cassiopeiae. With a wide-field Panoptic eyepiece giving 114x in my 12.5inch, it shows a chain of stars leading toward the center, sort of like a candied apple on a stick. Unfortunately, it's not plotted on Sky Atlas 2000.0; you'll have to mark it there yourself using the position in the table on the facing page. It's between two 6th- magnitude stars 1° apart.

NGC 659, our last open cluster in Cassiopeia, looks like a patch of Milky Way anchored by a pretty triangle of stars including 44 Cassiopeiae. I've never seen more than about two dozen stars in this cluster through any telescope. It's northwest of Delta Cassiopeiae, quite near the brighter clusters M103 and NGC 663. The three-cluster grouping looks great even in binoculars.

NGC 7380 in Cepheus is a triangular cluster embedded in a larger, faint emission nebula, Sharpless 2-142. I first observed this cluster from my back deck in San Rafael, California, on December 26, 1997, using my 12.5-inch reflector at 1 14x. Without a filter I can barely see the nebula, but a narrowband 0 III or UHC filter significantly increases its contrast with the sky.

NGC 253 is a big, dusty, nearly edge-on galaxy in Sculptor famous from photographs. I've observed it in every telescope I've owned, and it's one of my all- time favorites. If it weren't so far south in such a dim, out-of-the-way constellation it would be almost as well known as the Andromeda Galaxy, M31. And it's not that far south. If you can see Antares or Fomalhaut, you can see NGC 253.

My most memorable observations of it have been at Dillingham Airfield on the island of Oahu with the Hawaiian Astronomical Society. In 12.5-inch Strider at high power I see dark dust lanes, mottled lumpiness, and an oval core. In my larger 17.5-inch f14.5 Litebox (which I've named Hagrid), it takes on more substance and greater length. Clumpy starforming regions brighten dramatically into visible knots, and foreground stars appear embedded in the galaxy south of the dust lane. Caroline discovered this glorious object on September 23, 1783, and it is the first object of Herschel's Classification V: "very large nebulae?"

Ml10 (NGC 205) is the dimmer, less condensed of the Andromeda Galaxy's two elliptical companions. My first observation of M110 was in October 1989 on my back deck with Stardust, my homemade 10-inch f/7.3 reflector. I sketched each new object I observed, and those early sketches are amusing to look at now. My sketch looks like a smudged oval, a little brighter in the middle. It was my 29th Messier object and my first Caroline Herschel. She discovered it and the next object, NGC 891, on the same night, August 27, 1783. What a night that must have been!

NGC 891 in Andromeda is a classic edge-on galaxy with a dust lane down the middle. It holds a special place in both my heart and logbook, being one of the first deep-sky objects I viewed through 12.5-inch Strider. Despite its fame it is dim the dimmest of the C. Herschel objects - and has a low surface brightness to boot. But this elongated spindle of light looks unusual in any telescope that shows it at all. You're not likely to detect the central dust lane, however, in less than a 12-inch.

The author preparing Hagrid, her 17.5-inch Litebox reflector, for a night of viewing at Lake Sonoma, California, one of her favorite observing sites.