First Views: The Whirlpool Galaxy

With the elegance of Archimedes's perfect spiral, the flowing form of the Whirlpool Galaxy (M51) in Canes Venatici is one of the most beautiful in the heavens. The dark lanes so perfectly separate the winding arms, it's no surprise this was the first galaxy to have been called a spiral.

To appreciate the Whirlpool, you first need to get away from the crippling light pollution of the city. Otherwise, you're left with a small, disappointing fuzz around a bright nucleus. But under the cover of darkness you can easily find it with binoculars, just off the handle of the Big Dipper, and you can even tell it's elongated.

The first human to lay eyes on the Whirlpool was the renowned French comet hunter Charles Messier, on October 13, 1773. Despite the optics of his day, the 3- to 4-inch telescopes showed Messier that the "nebula" was double. Ushering in the age of the spiral nebulae required the prowess of the 3- and 6-foot-diameter mirrors of Lord Rosse of Ireland. He used a polished copper-tin alloy called speculum and saw a spiral form years before film was sensitive enough to make the fact widely known.

Even to this day, Lord Rosse is unfairly judged about his "imaginative" and "whimsical" drawing of the Whirlpool. If you compare it to the detailed and precise drawing he and his assistants produced later, you'll see that the first simply captures the character of the spiral. Over the years, Rosse tried with his 72-inch "leviathan" telescope to measure the orbital motion of the field stars around the nucleus. Little did he suspect that M51 was millions of light-years in the background.

With a 12-inch scope, you can track down every star in Rosse's drawing, some of which are actually knots in the spiral arms. These HII regions are similar to the Milky Way's Orion Nebula. Note how the "connecting" bridge fades out in the drawing. The bridge is truly one of the toughest details to view in the Whirlpool, and many observers trick themselves into believing they see it, having the picture of the bridge captured in memory.

An 8-inch telescope will reveal some of M51's structure. Yes, it requires patience, magnification, and dark adaptation. Lord Rosse complained that every time he used a feeble lamp to sketch a delicate feature, it took minutes before his eyes regained sensitivity. A dark cloth over your head will help.

Roger Clark, in his book Visual Astronomy of the Deep Sky, recommends a wide range of magnification, maxing out past 300x even for an 8-inch scope. This is the only way to see fine structure in the bright sections of a deep-sky object, even though the fainter veils will disappear.

Center the object in the field of view and then glance to the side. This "averted vision" technique uses the sensitive rods in your eyes to detect faint light. Savor the view; take more than 30 minutes to absorb the wealth of detail in the Whirlpool.

Lord Rosse

Lord Rosse

23 March, 2000

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