The Deep Sky

In mythology, the small constellation Canes Venatici, just south of the Big Dipper's handle, represents a pair of hunting dogs.  Today's observers, however, remember the hunting dogs for retrieving an impressive selection of galaxies.  Canes Venatici reaches midnight culmination in early April.  The constellation passes close to the zenith in the early evening hours of May and June.

M106 (NGC 4258).  Let's begin the tour of Canes Venatici at M106, an outstanding example of an Sb spiral.  Even through suburban skies, finderscopes will reveal it as a faint smudge near a faint field star set just east of the halfway point between Phecda [Gamma Ursae Majoris, the southeastern star in the Big Dipper's bowl] and Chara [Beta Canum Venaticorum].

Through a 4-inch telescope, M106 shows a bright, oval disk which, to me at least, looks a little like an underinflated football!  Eight-inch instruments begin to add some mottled definition to the spiral halo along with a bright central nucleus.

Many observers comment with some surprise at the small size of M106.  Though long-exposure photographs reveal M106 to span about 18'x 8', most visual reports suggest a much smaller extent; the discrepancy probably due to the low surface brightness of the galaxy's spiral arms.  A 12-inch barely reveals these arms on exceptional nights, and only the largest amateur telescopes have sufficient light-gathering ability to show the full breadth of M106.

M94 (NGC 4736) lies a little northeast of the halfway point between Cor Caroli [Alpha Canum Venaticorum] and Chara [Beta Canum Venaticorum].  An Sa spiral, M94 looks nearly circular, with the faint spiral halo enveloping a bright center.  Many describe it as looking like an unresolved globular cluster, as any spiral structure in the galaxy's arms is only seen on long-exposure photographs.

Though most references and catalogues rate the magnitude of M94 within a couple of tenths of M106, it strikes most observers as glowing distinctly brighter.  This effect is probably due to their comparative sizes.  M94 exhibits a higher surface brightness than its neighbor since its light spreads across a smaller, 11'x 9' area.

M63 (NGC 5055), a 9th-magnitude Sb galaxy, is nestled in a barren naked-eye field about two-thirds of the way from Alkaid [Eta Ursae Majoris], at the end of the Big Dipper's handle, to Cor Caroli [Alpha Canum Venaticorum], brightest star in Canes Venatici.  You'll find it a little north of a distinctive four-star triangle.

Although often ignored by observers because of its sparse surroundings, M63 is bright enough to be seen with 10x binoculars on clear, dark nights.  Small telescopes display it as a silvery sliver of light brightening, at first slowly, then rapidly, toward an inner core.  An 8-inch telescope adds a centralized stellar nucleus, while larger instruments also hint at a mottled surface to the tilted spiral arms.  Measuring 12'x8' in long-exposure photographs, M63 bears magnification well, with the best views coming between 150x and 200x.

M51 (NGC 5195).  Of all the countless galaxies scattered across the sky, none exhibits as much detail as M51, the renowned Whirlpool Galaxy.   To find it for yourself, start at Alkaid [Eta Ursae Majoris], the end star in the handle of the Big Dipper.  Hop to 24 Canum Venaticorum, a 4th-magnitude point just 2° to the west-southwest, then slide another 2° to the southwest to a trapezoid of faint stars.  M51 lies inside the trapezoid's northeast corner.
 
The Whirlpool Galaxy is a classic example of a face-on spiral galaxy.  Its pinwheel structure, first detected with Lord Rosse's enormous 72-inch reflector in 1845, was originally thought to represent a solar system in formation.  Only after Edwin Hubble conceived the true galactic organization of the universe was M51 and countless other "spiral nebulae" recognized as remote galaxies.

While it may have taken a 72-inch telescope to discover the spiral arms of M51, today's amateur astronomers can see hints of them in much less.  From dark, clear sites, high-quality 6- to 8-inch instruments can readily show the pinwheel-like arms of M51 wrapping around its bright central core; a 12- to 14-inch scope yields the same appearance even through suburban skies, as shown in Eyepiece Impression 1.  Large amateur  instruments note a distinct mottling to the spiral arms, the result of bright and dark patches of nebulosity.

Extending toward the north of M51 is its famous companion galaxy NGC 5195.  Although Messier discovered M51 in 1773, the companion went undetected for another eight years until Pierre Mechain spied it.  Both galaxies are clear in even the smallest amateur telescopes, and may even be spotted through 7x binoculars by keen-eyed observers.  NGC 5195 is an irregular galaxy, appearing as a fuzzy, not-quite-round glow seemingly linked to M51 by a luminous bridge of nebulosity (in reality, this is apparently an optical illusion).

M3 (NGC 5272), the finest globular in northern springtime skies, was discovered by Messier in 1764.  The simplest way to find M3 is to aim your telescope just shy of the halfway point from Arcturus [Alpha Boötis] to Cor Caroli [Alpha Canum Venaticorum], then take a look through your finder.  M3 should be at or very near the field of your finder, looking like a fuzzy star just northeast of a 6th-magnitude sun.

Messier's telescope showed his catalogue's third entry as little more than a hazy smudge, while Eyepiece Impression 2 is typical of the view through a modern 8-inch instrument, with hundreds of fine stellar points surrounding the cluster's moderately compressed nucleus.  By doubling the telescope's aperture, stars are resolved across the cluster's face, with several creating lines or strings.  William Herschel was first to spy these unusual features, describing them as "star chains."  Can you duplicate Herschel's find through your own telescope?