Andromeda’s NGC891 and Beyond

Enjoy the autumn sky’s best edge-on galaxy.

Brecher-NGC891

NGC891 is Andromeda’s other show-piece galaxy. Courtesy Ron Brecher

Imagine the textbook edge-on galaxy: a spindle-shaped cloud with tapered ends, a bright central hub and a long, bisecting dust lane. This describes my favourite edge-on, NGC4565, in the spring constellation Coma Berenices. Yet even that superb specimen isn’t precisely edge-on; it is tipped very slightly to our view. Autumn’s prime example, NGC891, in eastern Andromeda, lies almost exactly edgewise.

NGC891 chart

GOING THE DISTANCE Almost midway between second-magnitude Almach, in Andromeda, and the loose cluster M34, in Perseus, lies the 10th-magnitude edge-on galaxy NGC891, shown faintly in the above illustration. The blue circle (diameter 0.75 degree) encloses a remote cluster of galaxies known as Abell 347. If you observe some of the galaxies in Abell 347, you are among a small elite group of humans who have actually seen galaxies 250 million light-years away. (Click on the chart for a full-size version.) Cartography by Glenn LeDrew

NGC891 is a 3½-degree star-hop east of the showpiece binary star Almach, or gamma (γ) Andromedae. Almach’s colourful components — a second-magnitude yellow star and a fifth-magnitude blue star, nearly 10 arc seconds apart — make a gorgeous pair in my 4.25-inch Newtonian reflector at 54×. After admiring the binary, I push toward the galaxy, which, although fairly large, is dim and easy to miss. Fortunately, 3¾ degrees east of Almach isb an orangey 6.7-magnitude landmark star called HD 14771. The warm hued star is a handy marker because wispy NGC891 floats a mere ⅓ degree northwest of it. (Beware of a whitish 5.8-magnitude star vying for your attention ¾ degree south of HD 14771.)

Roughly 30 million light-years from Earth, which is close by cosmic standards, NGC891 sports a total visual magnitude of 9.9. However, some of the galaxy’s light is blocked by a thick dust lane, and the rest is spread across an area about 12 by 1.5 arc minutes in extent. Consequently, NGC891 suffers from low surface brightness. Even so, this pale prize materializes in my 4.25-inch in suburban skies, well away from the worst city glow — a reminder that sky conditions are at least as important as telescope aperture for detecting faint objects. Low power picks up only a ghostly sliver oriented north-northeast by south-southwest, but the spindle shape emerges with increasing magnification. A 12th-magnitude star shines on the west side of the spindle north of the brighter fat midsection, while a fainter star wavers on the edge of visibility at the galaxy’s southwest tip.

Karlsson-NGC891

NGC891 as sketched by John Karlsson at the eyepiece of his 15-inch Dobsonian reflector.

Observing NGC891 with my 10-inch and 17.5-inch Dobsonians reveals the expected diffuse, tapered disc with its strongly elongated bulge. In the 10-inch at 150×, the threadlike dust lane clearly bisects the bulge, but oddly, that dark divider doesn’t span the galaxy from tip to tip. In the 17.5-inch at 222×, my eye traces it farther along the southern wing than the northern wing. This perceived asymmetry is a contrast effect caused by the disc’s being unevenly bright. The southern wing is slightly more luminous than the northern wing, so the dark lane stands out better along that southern section. In addition, a number of clusters and nebulas (visible in images) interrupt the northward dust lane. The unevenness shows in the sketch of NGC891 (above) made by Vernon, British Columbia, deep-sky observer John Karlsson using his 15-inch Dob.

There’s more cosmic treasure near the big edge-on. Remember my orangey landmark star? Less than ¼ degree southwest of that star is NGC898, another edge-on galaxy. Dim (magnitude 12.9) and tiny (2.0 by 0.5 arc minutes), NGC898 is, nonetheless, a fairly contrasty patch that my 10-inch picks up at high power. And marginally more than ⅓ degree southeast of the orange marker is 12.2-magnitude NGC910. (Note: A straight line drawn from NGC891 past the marker star leads directly to NGC910.) Only 1.5 arc minutes in diameter and of relatively low contrast, NGC910 is actually a tougher catch than NGC898. Underwhelming, both!

But here’s the thing: Both NGC898 and NGC910 are roughly 10 times farther away than NGC891. They belong to a remote cluster of galaxies called Abell 347 that spans an area of sky about one degree in diameter. Abell 347’s 15 brightest members range between 12th and 15th magnitude. If the night is very dark and the atmosphere steady, I can glimpse eight lumps of light in my 10-inch scope and all 15 in my 17.5-inch. Challenge yourself to see how many you can count.

Identifying the individual galaxies of Abell 347 is truly satisfying. But what I enjoy most is simply staring, fully dark-adapted, into a high-power eyepiece as the lumpy sky forms at the threshold of vision. A subtle effect, yes, but awe-inspiring just the same.

Contributing editor Ken Hewitt-White has observed deep-sky fuzzies over southern British Columbia for four decades.

Categories: Clusters, Nebulas, and Galaxies
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