A cosmic rabbit hole in the tail of Leo will take you to Abell 1367, a wonderland of galaxies more than 300 million light-years from Earth. Step in and lose yourself in the vastness.
Care to join me for a little adventure? There's no better time to stalk external galaxies than on April nights, when the dusty Milky Way hunkers along the east and west horizons, giving center stage to the hordes of spiral, elliptical, and irregular galaxies that cross the meridian from nightfall till the wee hours.
Tucked in the tail of Leo, the Lion, just 5.5° north of the bright star Denebola, you'll find one of the brightest galaxy clusters in the sky, Abell 1367. Also known as the Leo Cluster, this fabulously rich degree of sky contains some 70 major galaxies and many minor ones. On a dark, moonless night, an amateur astronomer with a 10-inch or larger telescope and an hour or two to spare might pick off nearly 100 fuzzy, extragalactic cocoons residing more than 300 million light-years from Earth, or 120 times farther than the Andromeda Galaxy. Far out, man.
The brightest galaxies in the cluster shine around magnitude +12.5 to +13 with the majority a magnitude and more fainter. Sounds challenging, doesn't it? Yes, but take galaxy magnitudes with a grain of stardust. You can almost always see deeper and fainter than you think if you follow these guidelines:
- Dark skies: Start out on the right foot by finding the best, un(light)polluted skies in your area and observe when the target is near the meridian. Abell 1367 culminates in the southern sky around 10 p.m. local time in late April.
- Dark adaption: Allow at least 15 minutes for your eyes to get "owly."
- High magnification: Start with low magnification to get oriented, then switch to between 200–250× when you're ready to really dig in. At low powers, you'll only see the brightest galaxies in a cluster. High magnification expands the apparent size of the smaller and fainter objects, allowing the eye to distinguish them from the sky background. Don't go too high, though, or these faint fuzzies will be so spread out, they'll disappear!
- Averted vision: At night, we use our rod cells to find our way in darkness and soak up photons from dim galaxies. Rods are concentrated away from the center of vision, so to see faint things more clearly, play your gaze around the object rather than staring directly at it. Averted vision will get you at least a magnitude deeper. For more deep-sky observing secrets, read Alan MacRobert's excellent article, Observing Secrets of Deep-Sky Objects Revealed.
Most dense galaxy clusters are dominated by elliptical galaxies that grow to titanic sizes through the merger of smaller galaxies members as they fall toward the center of the cluster. Abell 1367 is a little different from other rich clusters in having a sizable population of spiral galaxies. Astronomers interpret the significant number of spirals as a sign of the cluster's relative youth.
That's not the cluster's only stand-out attribute. Its brightest member, the heavyweight 12th-magnitude elliptical galaxy, NGC 3842, possesses one of the largest black holes of any galaxy known with a mass of 9.7 billion suns.
The cluster, along with the Coma Cluster (Abell 1656), form the heart of the Coma Supercluster, the nearest supercluster to our own Virgo Supercluster and the heart of the Great Wall, a huge filament of galaxy clusters and superclusters 500-750 million light-years long said to be one of the largest structures in the observable universe. Abell 1367 forms the Wall's "near" end, with the far end represented by rich clusters in Corona Borealis and Hercules.
Finding your way to Abell 1367 couldn't be easier. Center your finder on 4.5-magnitude 93 Leonis, look through a low magnification eyepiece, and you're there! The star is pinned to the cluster's eastern edge. Using the maps, you can star hop from there, stopping at small clumps of galaxies, while edging ever closer to the cluster's core, a magnificently busy downtown where careful scrutiny will repay with a brain-boggling 10 or more galaxies visible in the same 200× field of view.
What I especially like about exploring this cluster are the numerous conveniently placed field stars you can use to navigate this galactic archipelago. The stars also help greatly in pinpointing some of the fainter members. I'll use two or three stars to create a figure, say a triangle or trapezoid, with the sought-for fuzzball at one apex. Once you know exactly where to look, bear down with averted vision, and give it all you've got. Using stars to create makeshift geometric figures will make your hunt easier and more successful.
Rather than make a list of all the galaxies, I've selected a few to highlight. As you might expect, the NGC galaxies are generally larger and brighter than the other cluster members, but not always. Some of the small CGCG objects (Catalog of Galaxies and Clusters of Galaxies) and UGC galaxies (Uppsala Galaxy Catalog) were equally easy to spot.
- NGC 3873 — Magnitude +13.3. Bright, compact elliptical with a bright stellar nucleus. Touches fainter NGC 3875 to the east.
- NGC 3861 — Magnitude +12.7. Large, easy spiral with a bright, nearly stellar nucleus. I couldn't discern tiny, 15th-magnitude MGC +3-03-94 poking out of its southeastern edge. Note to self — use higher magnification next time.
- NGC 3860 and companions — Magnitude +13.4. A fuzzy, oval glow with a stellar nucleus located just north of three smaller CGCG galaxies. CGCG 97-114 was faintest, a diffuse patch of haze shining at photographic magnitude +15.3 (+15.3p). Persevere and use averted vision to dig out this rad tetrad.
- CGCG 97-88 and companions CGCG 97-93 and 97-94 — The first was relatively easy at magnitude +15.2p, but CGCG 97-93 (mag. +15.5p) and CGCG 97-94 about cracked my eyeball at magnitude +15.7. Both appeared as faint wisps at the limit of vision.
- IC 2951 — Magnitude +13.6. Bright spiral, noticeably elongated east-west with a bright stellar nucleus. A magnitude +13 star touches the eastern end. Smaller, fainter but similarly elongated UGC 6683 lies 1′ to the west. Nice pair!
- Cluster core / NGC 3842 — In the space of just 10′ at least 11 galaxies pop into view here, dominated by the blobby NGC 3842, a large elliptical with a bright, non-stellar nucleus. I've seen it listed at both magnitude +11.8 and +12.8, so we'll just call it +12. Four small smudges, PGC 36468 (very faint), CGCG 97-90, and NGCs 3841 and 3845 (all easier to spot), ride up along the galaxy's west side.
But the real celebrity in my opinion is the faint, evanescent UGC 6697 that flashes in and out of view like the momentary glimmer of a salmon leaping a waterfall. This magnitude +13.7 needle of light is a peculiar spiral galaxy undergoing a massive wave of star formation. As it plunges toward the center of the cluster at several million miles per hour, cold gas clouds within UGC 6697 are compressed by the hot gas that permeates the cluster. The massive new stars that result from this process will self-destruct as supernovae 10 million years later.
I saw 42 galaxies in Abell 1367 in just one evening in my 15-inch scope, but I'm eager to return because there's are at least 20 more calling my name. Exploring distant clusters whisks our imagination to the furthest reaches of the universe. I wish you happy hours climbing the Great Wall of galactic light in the deepest hours of a dark night.