Springtime (in the Northern Hemisphere) is galaxy time for deep-sky observers, for three reasons. On spring evenings the Milky Way lies right down on the horizon, keeping its own telescopic distractions out of sight. Second, the absence of the Milky Way allows us a wide, clear view into inter-galactic space with little or no interstellar dust in the way. And smack in the middle of this open view is the Virgo Cluster of galaxies — the core of the much larger Local Supercluster of galaxies, which is splashed across more than a dozen surrounding constellations (and includes, on its outskirts, our own Milky Way).

Tonight's telescopic guided tour begins at the star Denebola, Beta (β) Leonis, the tail tip of Leo just a few degrees from Virgo.

Most galaxies are notoriously dim. Their surface brightnesses, naturally enough, are similar to that of the Milky Way band crossing our sky. Of course their enormous distances make them appear small; the ones on tonight's list range from about 30 to 60 million light-years away. But surface brightness, the light per square arcsecond of sky (Sky & Telescope: January 1997, page 118), is unaffected by distance and is not even greatly affected by whether you're using a telescope or the naked eye. So if the light pollution in your sky hides the Milky Way, expect it to hide most parts of other galaxies too.

Luckily, most galaxies contain a much brighter nucleus or central region. (We can't see the bright core of the Milky Way because it's hidden behind interstellar dust.) So at least the central parts of many galaxies can be seen through even very mediocre skies.

I used a 6-inch reflector at 70x to scout out the sky tour here. My naked-eye limiting magnitude was a typical suburban 4.8. In a sky like this the Milky Way is just visible if you know where to look for it (when it's up), but it shows little or no detail and attracts no attention. If your skies are better than this, you'll have an easier time than I did.

Star Chart Basics and An Intitial Hop

Before starting out, make sure you have a good feel for how to use the map outdoors at your telescope. The black circles on the map are 1° in diameter, the size of the view that fills a typical 40x or 50x eyepiece. If you use higher power to help penetrate light pollution, as I did, be prepared to see a proportionally smaller area of the map in your view.

North is up on the map. Nudge your telescope slightly toward Polaris and note which side of the view new stars enter from; that's celestial north. Turn the map around so its north side matches this direction.

Lastly, make sure your telescope gives a correct image rather than a mirror image; the light going through the telescope should be reflected an even number of times (zero counts as an even number). This may mean removing a right-angle star diagonal at the eyepiece. You need a correct image if you want to easily compare what you see to a map.

If you do observe with a mirror image, you can scan the map into an image-processing program, flip the image right-for-left, and print it out as a mirror image; this will match your view.

Let's get started!

1. Denebola. Our jumping-off point is the second-brightest star in Leo, magnitude 2.1. It hangs just a few degrees over Virgo's head. In my 6-inch, Denebola appears a definite pale blue-white — slightly surprising considering that its spectral type is A3 and its color index is +0.1. This is only the tiniest bit to the blue side of the spectral type and color index often considered to be pure white (A5 and +0.2). Denebola is a beautiful diamond gem, the first and last really bright object on our night's itinerary. It is 22 times as luminous as the Sun and is located 40 light-years away.

2. h2583. Carefully star-hop to this 9th-magnitude double star 1.7° southwest from Denebola, matching star patterns on the map to what you see in the eyepiece each step of the way. Pay special attention to triangles of stars, particularly their exact shapes. Triangles are the basic steppingstones for star-hopping.

If you've got the map correctly oriented to north, and have the mirror image vs. correct image issue straightened out, you'll have no problem making your way to this little double. It is named with a lowercase "h" for its number in the 19th-century double-star catalog of John Herschel, son of William Herschel, who was capital H. In my 6-inch it's an attractive little pair of identical white points, wide and easily separated, like distant animal eyes in the dark. Not all the pretty double stars for small telescopes are the bright ones listed in observing guides!