Explore Caroline Herschel's Celestial Showpieces

Because of COVID-19 restrictions many of us have found ourselves doing a lot of solo observing this year. Virtual star parties and online Zoom meetings have helped to connect us, but they only go so far. I needed a friend. Maybe that's why I was drawn to Caroline Herschel and her lovely catalog of deep-sky objects.

I read about Caroline's life, her comet discoveries, and how she came to be recognized for her contributions — and felt a connection. So I got a copy of her deep-sky finds and devoted one night and one early morning to tracking down all 14 of them. Most were original discoveries, but a couple, like M110 and IC 4995, were independent observations of objects seen in years prior by others but unbeknownst to Caroline at the time.

Herschel lived a less than ideal life as a servant in her own home in Hanover, Germany in the latter half of the 18th century. Because she was disfigured by smallpox and typhus her mother assumed she'd never find love and marry (as was expected of young ladies at the time), so she put her to work. It wasn't until her brother William invited her to join him in England that her situation began to improve. He was a musician and choirmaster in Bath, and she began learning to sing. But William's interests soon turned to astronomy, and Caroline left her musical career behind to become his assistant.

She not only helped him grind ever-larger mirrors but took notes of his observations. While she sat at a desk at an open window, brother Bill would call out descriptions and reference stars out from atop a tall ladder at the telescope's eyepiece. They made a capable team. For her assistance Caroline received a salary of £50 a year from the British king George III, making her England's first professional female astronomer.

But I get ahead of myself. Earlier, while her brother busied himself with double stars and the newfound fame that attended his discovery of Uranus, Caroline began searching the sky on her own. She discovered her first comet, C/1786 P1, in August 1786 with one of William's telescopes. Not only was she the first woman to find a comet, but she went on to discover seven more!

For her deep-sky discoveries Caroline used a small, spyglass-like refractor before William built her a 4.2-inch richest field reflector. With them she uncovered more than a dozen star clusters and galaxies, inspiring William to undertake his own study of the deep sky with larger instruments.

Together they discovered and described 2,500 galaxies, nebulae, and star clusters and compiled them into the Catalogue of Nebulae and Clusters of Stars. This work became the foundation for the New General Catalogue of Nebulae and Clusters of Stars (NGC) used by amateur and professional astronomers to this day.

Maybe it was pandemic isolation working on my imagination, but I felt Caroline's presence at my side as I eased the telescope from one deep-sky object to the next. I wanted to ask her how she managed to keep warm back on February 26, 1783, while making her first discovery — the star cluster NGC 2360 in Canis Major — in that tiny refractor. I wanted to know which were her favorites and to hear her retell one of her strongest childhood memories, a winter night her father took her out to see the stars "to make me acquainted with the most beautiful constellations . . . ."

Caroline must have relished these sights as much as I. Even more, as she was the first person on Earth to set eyes on most of them.

Each is described below starting with objects visible in the western sky at nightfall and moving east to the pre-dawn sky. Following the name is the object's type (OC for open cluster and GX for galaxy), magnitude, and discovery date. All the objects in Caroline's catalog — except NGC 2360 and M48 — are currently visible at nightfall in the evening sky. For more details on discovery dates and duplicate observations, click here. I also recommend this excellent article by Sky & Telescope's former editor Tony Flanders.

IC 4665 (OC) — Ophiuchus — magnitude 4.2 — September 27, 1783
Sometimes referred to as the Summer Beehive. A beautiful sight in 8×40 binoculars. A bright, rich cluster with nearly 60 stars gathered in a circular patch 1.1° across. Well-resolved and a pretty sight! Even at low magnification (64×) my 15-inch spreads this one out too much, but the even spacing of the stars, including about 10 members of 7th magnitude, does indeed recall the Beehive (M44) in Cancer. Caroline said this: "A cluster of stars. I counted about 50 in the field; rather more than less."

NGC 6633 (OC) — Ophiuchus — 4.6 — July 31, 1783
Like you, I often see shapes in clusters and nebulae. Don't laugh, but in binoculars this little beauty looked like a Milk-Bone dog treat with one end broken off. More than 150 stars crowed into 20′ of space which gives the cluster a bright, scintillating appearance in my glass. In the 15-inch its many members outline a wizard's cap with the tip pointing southeast and the floppy brim northwest. No word yet on whether I'll be inducted into Gryffindor, Slitherin, or Hufflepuff. NGC 6633 lies 1,018 light-years from Earth — about twice as far as the Beehive Cluster — and is visible without optical aid from a dark sky.

NGC 6819 (OC) — Cygnus — 7.3 — May 12, 1784
Wow! If you only see one of Caroline's treasures make it this one. Hard to believe but this 5-arcminute-wide cluster hosts more than 900 stars. Visible in binoculars as a faint patch, in the 15-inch at 64× and 142× it's so rich and compressed I nearly got sucked through the eyepiece. For fun I tried counting stars but gave up after 150. Many members are fainter, no surprise given the

bunch hails from 6,700 light-years away.

NGC 6866 (OC) — Cygnus — 7.6 — July 23, 1783
Measures 15′ across with around 125 members. Though not compressed like NGC 6819 it's obviously elongated east-west and stands out well in the low power field of view. Stars in its circular core are evenly spaced and appear nested within a flattened "ring" of other cluster members, the whole of which reminded me of a connect-the-dots version of Saturn and rings.

NGC 7380 (OC+nebula) — Cepheus — 7.2 — August 7, 1787
A V-shaped cluster that reminded me of the Hyades but filled with stars and veiled by faint nebulosity visible at 64× with averted vision. With an O III filter in place the glow of excited hydrogen was obvious not just across the cluster but issuing in a thick, faint plume from the open end of the V.

Also known as the Wizard Nebula, this young cluster-nebula creates and cuddles newborn stars 7,200 light-years away. I doubted Caroline would have seen the nebula in her small instrument, so I let her know about the new development out loud that night. I never mind talking into the dark when I'm observing alone. You too? We instinctively need to express ourselves whether another is physically present or not.

NGC 7789 (OC) — Cassiopeia — 6.7 — October 30, 1783
One of my lifelong favorite star clusters. Caroline called it ". . . a fine nebula. Very strong." In binoculars I discern a misty, granulated puff of stars hinting at great things to come in the telescope. Indeed 580 stars crowd into less than half a degree, a sight that will knock you back a step at first sight. Wow to the power of 10 here. And it's not just the stars that grab you but the phantom dark lanes that arc and whorl through the cluster's core. They almost look like dark nebulae. No wonder this object is also known as Caroline's Rose. You could just as easily be staring at a black blossom edged in stellar frost. Thank you, Caroline, for putting this stunning object on the map.

NGC 659 (OC) — Cassiopeia — 7.9 — September 27, 1783
Visible in binoculars as a small patch of fuzz, the cluster resolves into 80-plus stars (actually membership is ~180) arranged in two clumps east and west separated by a dark vacuity. Each half features a similar close double star with a separation of 4″–5″ — a 9th-magnitude pair in the eastern half and a 10th-magnitude duo in the west.

NGC 189 (OC) — Cassiopeia — 8.8 — September 27, 1783
The faintest of Caroline's clusters and rather sparse too with a couple dozen members to its name. Just the same, it stands out well in the field of view at low magnification.

NGC 225 (OC) — Cassiopeia — 7.0 — September 27, 1783
In binoculars this is an easily visible milky patch speckled with a few faint stars located midway between Gamma (γ) and Kappa (κ) Cassiopeiae. In the 10-inch telescope at 64× I see a loose group of about 35 stars (75 total members) with a distinct arc of four bright and one faint star bordering the cluster's southeast side.

NGC 205 = M110 (GX) — Andromeda — 8.1 — August 27, 1783
The fainter and larger of the Andromeda Galaxy's two brightest companions. Visible in binoculars this dwarf elliptical galaxy is elongated north-south and located 0.5° northwest of Andromeda nuclear region. It appears as a smooth oval with a brighter core also elongated north-south. Increasing the magnification to 142× I discern a faint, starlike point at its center.

NGC 752 (OC) — Andromeda — 5.7 — September 29, 1783
A superb object in binoculars! Well resolved with about 75 stars visible in a patch 1.25° across. Rich with faint sparkles that make it glitter. Through the 15-inch I see loops and whirls of stars that extend beyond my lowest power field of view. The brightest member, flanked by two fainter stars, has a lovely golden color.

NGC 253 (GX) — Sculptor — 8.0— September 23, 1783
I'm amazed Caroline saw this given its low altitude from the British Isles. She described it as "a faint nebula below the 2^d Triangle under β Ceti . . . Mess. (Messier) has it not." It's not much higher from my location but what a sight on a dark night. At 142× this enormous galaxy, its shape reminiscent of Andromeda, extends from northeast to southwest across the entire field of view. The nuclear region is bright and mottled with a vague but wide, dark lane that cuts just north of the core. Several foreground stars centered on the nuclear region add charm and provide a 3D perspective.

NGC 2360 (OC) — Canis Major — 7.2 — February 26, 1783
Caroline's notes describe the cluster as "following Gamma (γ) Canis Majoris, a very faint Nebula." That would match its appearance in my 8×40s but doesn't come close to what a 10-inch reveals. A diverse mix of about 90 stars shimmer across 14′. The brightest members congregate along the cluster's northwestern corner in three vertical rows the way you'd plant your garden beans. The profuse fainter stars make a spray to the southeast. A beautiful sight!

NGC 2360 is often called Caroline's Cluster because it was the first she discovered. To see it you'll have to set the alarm and rise before dawn — I guarantee no regrets.

NGC 2548 = M48 (OC) — Hydra — 5.8 — March 8, 1783
Another binocular stunner! A ball of faint but resolved stars about 0.5° across. In the 10-inch at 45× the 80-some members spread languidly across the field of view with two bright pairs at center.

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