Sky Talk October 2009: The Great Spiral Galaxy in Andromeda

Nothing gets the blood of a stargazer pumping like hearing the words “spiral galaxy.” This enduring icon of astronomy is deeply rooted within us, partly because we live in one ourselves — the magnificent Milky Way Galaxy! (See past Sky Talk installments.) But there is one galaxy that stands out among all the other billions of its kind, and that’s the great spiral in the constellation of Andromeda.

Placed high in the northeastern sky these Fall evenings is one of the grandest objects in the universe — one subtly visible to the unaided eye on a dark clear moonless night, and a truly fascinating spectacle in binoculars and small telescopes. It’s the famed Andromeda Galaxy (also known as Messier 31), a near clone and companion of the Milky Way in which we live. But rather than being immersed within our Galaxy as we are, this one lies far beyond us some 2,500,000 light-years away.

It’s easily found thanks to the Great Square asterism of Pegasus, currently high in the sky facing south. Following an imaginary line from the bottom right corner star of the Square (actually a rectangle) to its upper left corner one (a star Pegasus shares with neighboring Andromeda) prolonged its own distance brings you to Beta Andromeda. This wonder of wonders lies just a short distance to the upper right of the star. To the unaided eye, it appears as a misty oval smudge of light that’s clearly non-stellar in appearance. Now switch to your Celestron SkyMaster binoculars from Edmund (#30311-02). Slow sweeping back and forth across the Galaxy’s bright central core, combined with the use of averted vision (staring off to one side of the object), you’ll find it spanning an area several times the apparent diameter of the full Moon!

If there ever was a galaxy made for viewing with the Edmund Astroscan Plus wide-field telescope, this is it! Its 16X low-power eyepiece delivers a brilliant field of view 3 degrees across, fully encompassing the Galaxy and causing it to seemingly float three-dimensionally in space (which it is!) behind the backdrop of stars in the Milky Way itself. Extending outward from the bright nucleus is its disk — an eerie oval glow some 2 degrees in size oriented northeast-southwest. Careful scrutiny will show its northwestern edge abruptly cut off by dark material — dust lanes lying within the galaxy’s spiral arms. You’re actually viewing detail including spiral structure in another galaxy!

But there’s still more to see! Just as our Milky Way has two companion galaxies (the Magellanic Clouds visible from the Southern Hemisphere), so does the Andromeda Galaxy. South of its core and just outside its disk is the small elliptical galaxy Messier 31, while the larger but fainter elliptical Messier M110 lies some distance northwest of the main galaxy beyond the dust lanes mentioned above. While both companions have been detected in big binoculars by experienced observers under good conditions, it takes a telescope like the Astroscan Plus (#30050-01) to make them obvious. M32 looks like a fuzzy star while M110 appears as a ghostly glow requiring averted vision to glimpse with certainty most nights. The trio remains visible well into Winter, affording ample opportunity to become intimately familiar with this wondrous sdenizen of intergalactic space.

–James Mullaney
Former assistant editor at Sky & Telescope magazine and author of eight books on stargazing.

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