Hidden Gems in Common Deep-Sky Objects

Many of the deep-sky objects we point our telescopes toward have pleasant surprises, some in plain sight, others hidden and more challenging. Let me introduce you to a few.

Deep-Sky Prizes

"Open up" a deep-sky object with your telescope and you never know what you might find in addition to the expected sights.
NASA / ESA / HST

As kids, we'd take our allowance and buy these boxes of Cracker Jack filled with caramel-coated popcorn and peanuts. I never much cared for the molasses-flavored popcorn, but the peanuts were tasty. Both took a backseat to the paper-wrapped prize at the bottom of the box.

Sometimes I'd fish out the prize before even bothering with the goodies, tearing it open to get something cool like a plastic T-rex, whistle, or even a magnifying glass.

Deep-sky objects are like that. You might seek out a galaxy and discover an unexpected double star in the same field of view. A star cluster may include a striking asterism or an appealing red star. But you've got to rifle through the popcorn and peanuts first to find the prize.

I've selected eight of my favorites, all well-placed in the evening sky this month. Most will be familiar to you and easy to see in any telescope, but I've included a few obscure and challenging objects, too. So many deep-sky objects hold additional rewards that come with repeated observation that narrowing it down to eight will only give you a taste of the treats. That's why I hope you'll share a few of your own deep-sky prizes and surprises at the comments link below. Without further ado:

M103 — Red star and a duplicitous double

A Messier Double Prize

The open cluster M103 in Cassiopeia has not one but two prizes: a striking red giant star and the double star STF (∑) 131.
Jim Misti

M103 is a favorite: a real sparkler of star cluster and easy to find about 1° east of Delta (δ) Cas in the "W" of Cassiopeia. At magnitude +7.4 and 6′ across, you can even spot it in binoculars. Through a small scope you'll notice that most of the cluster's ~40 members are neatly contained within a bright little triangle of stars.

Inside that figure, a lovely 10th-magnitude red giant will catch your attention, while the pretty double star Struve 131 (magnitudes +7.3, +9.9; separation 14″), at the group's northern apex, looks for all the world a bona fide cluster member. It's not. Like Aldebaran in the Hyades, it's a foreground star. M103 lies about a distant 8,000 light-years from Earth, and the double about 2,800 light-years.

Triangulum Galaxy totes a gargantuan nebula

Star-making Conglomerate

If you've never seen a nebula in another galaxy, M33 offers a nice prize: NGC 604. Even a 6-inch telescope will show it as a small knot in one of the galaxy's spiral arms. North is up.
Hunter Wilson Astrophotography

The Triangulum Galaxy holds many treasures for amateur astronomers — flocculent arms, stellar associations, a globular cluster, and multiple bright emission nebulae. Brightest and easiest of the emission nebulae is NGC 604, pinned to a spiral arm about 5′ northeast of the galaxy's center. Shining at magnitude +12 and a tad larger than 1′ across, this knot of nebulosity looks like a small comet until you realize you're seeing a stellar nursery 40 times larger than the Orion Nebula some 2.7 million light-years away! Use high power to see structure (smaller knots) and watch the blob pop in brightness through a nebular filter.

Double Cluster meets the Smiling Cyclops

Smilin' Back at Ya'

The Double Cluster — NGC 884 (left) and NGC 869 — aren't far from the "W" of Cassiopeia and form one of most spectacular stellar gatherings in the sky. Can you see the one-eyed Cyclops?
Hunter Wilson Astrophotography / SDSS (inset)

Every time I look at the Perseus Double Cluster, besides those breathtaking ganglia of stars, I always see a one-eyed, starry smile beaming from the center of NGC 869. The tiny asterism, nicknamed the "Smiling Cyclops" by amateurs Clayton Jeter and Will Young, will surely catch your eye if it hasn't already. The solitary "eye" is a bright, slightly variable magnitude +6.5 star. Just to its east lie five or so 9th-magnitude stars in a smiley arc. If you're not into smiles, the asterism also looks like a carat-busting diamond ring. Either way, it's a wonderful prize worth tearing off the wrapper as soon as the next clear night.

NGC 1023 hides a secret

Hiding in plain sight

NGC 1023 is a bright galaxy in western Perseus. Much fainter and practically hidden within the galaxy's outer disk is wispy NGC 1023A.
Jeff Johnson / CC BY-SA 3.0

High in Perseus, 5° due west of the Rho (ρ) Persei / Algol stellar duo, the barred lenticular galaxy NGC 1023 makes for a pleasant diversion from winter's plethora of star clusters and nebulae. The 8′ × 3′ east-west elongated streak has a bright central bar and near-stellar nucleus; at magnitude +10, the galaxy requires only a 6-inch telescope. But something else lurks here for those who love a challenge — a 13.6-magnitude companion galaxy with the name of NGC 1023A (a.k.a. PGC 10139). It's barely visible superimposed on NGC 1023's eastern extension.

If you have a 12-inch or larger scope, select a magnification from 150×–250× and use averted vision to look for a misshapen bulge at NGC 1023's east end, a sign of its barred, irregular galactic companion.

Multiplying multiple stars

Stellar Multiplication

Sigma Orionis (center) and the triple star Struve 761 will add a lot of sparkle to your wintertime observing. The inset shows the stars' labels and separations.
Peter Wienerroither / Sky & Telescope (inset)

Fourth-magnitude Sigma (σ) Orionis, located 50′ southwest of Alnitak, the easternmost star in Orion's Belt, is one of the finest multiple stars for small telescopes. Even a 6-inch will show the bright primary accompanied by a short, scraggly line of three companions. The faintest is C at magnitude +10. Sigma itself, also known as Sigma AB, has an extremely close magnitude +5.1 companion (B) only 0.25″ west-southwest of the primary. A 12-inch in excellent seeing at a magnification of 350× or higher might be able to cleave this one or at least show Sigma AB as elongated. I've yet to see it.

When viewing double and multiple stars, I suggest using the lowest magnification necessary to split all components. Too high a magnification can rob these gems of the crispness that make them so aesthetically pleasing.

More Surprises!

This photo labels the brighter stars in the Sigma Orionis Cluster.
DSS / CC-BY-SA 4.0 / Wikipedia

Ready for your prize? Just 3.5′ northwest of the stellar conga line, you'll be drawn to another multiple star, Struve 761. This trio of 8th-magnitude stars form a skinny triangle that together with Sigma pack the field of view with gobs of bling. A beautiful sight!

If that's not enough, the Sigma quadruple forms the core of a star cluster discovered only in 1996 called, appropriately, the σ Orionis Cluster. That year, a large number of low-mass, pre-main sequence stars were discovered centered on the bright star. You can further your explorations of the cluster with the help of the photograph above.

Moths drawn to a celestial candle

Irresistible Attraction

NGC 2362, better known as the Tau (τ) Canis Majoris Cluster after its brightest member, 4.8-magnitude Tau, looks like a gathering of moths around a central flame even in smaller telescopes. The cluster is located 2.5° northeast of Delta CMa, the northernmost star in the "triangle" of bright stars in the southern half of Canis Major.
Paulo Cacella

"Where have you been all my life?" That was my reaction on first seeing the sparkly star cluster NGC 2362 in Canis Major. Some 40 stars gather into 6′ of sky under the bright umbrella of Tau. Few clusters are so dominated by one overpowering star, in this case a rare, blazing hot, blue O supergiant. Take a closer look for its two companion stars, magnitudes +10.5 and +11.2, 8.5″ and 15″ away, respectively, in P.A. ~90° (east).

Like some planetary nebulae that flash in and out of view when switching between direct and averted vision, the contrast in brightness between Tau and the other cluster members plays a trick on our eyes. Star directly at Tau, and you'll see only a smattering of stars around it, but glance off to the side and the group blooms like a field of stellar flowers!

Care for a doughnut with that cluster?

Loopy Interloper

The rich open cluster M46 appears to harbor NGC 2438, but the planetary nebula is actually a foreground object moving at a different velocity from the cluster. The nebula's apparent central star, visible in smaller modest telescopes, actually belongs to M46. The true central star shines faintly at magnitude +17.5. Click for a spectacular closeup of the nebula.
Jose Luis Martinez / CC BY-SA 4.0

The classic case of a surprise buried inside a familiar deep-sky object has to be the little doughnut-ring planetary nebula NGC 2438 superimposed on the bright, rich star cluster M46 in Puppis. The cluster tantalizes even in a 50-mm finderscope, looking like an atomized mist of minute pinpoints. In a 6-inch telescope, M46 spans ½° and if you care to count, there are some 150 stars salting the field.

The arcminute-wide, magnitude +11 planetary nebula looks like a small, gray puff some 10′ north of the cluster's center. Even a 6-inch scope will grab it. Averted vision reveals a dark center and a faux central star that's actually a member of the background cluster. For your best view of this smoky ring, use a UHC or O III filter. You'll be amazed at how much crisper this doughnut will appear. And who doesn't like a crispy doughnut?

Star vs. galaxy

Battle of Bright vs Faint

Glare from nearby Regulus nearly swamps the Local Group galaxy Leo I, located 20′ to the star's north. The dwarf spheroidal galaxy lies some 800,000 light-years away, spans 10′ across, and shines weakly at magnitude +11.2. Regulus's companion is the bright star immediately to its lower left. South is up.
Chris Cook (www.cookphoto.com)

Regulus is Leo's brightest star and a pleasing small scope double. The huge brightness range between the 1st-magnitude primary and 8th-magnitude secondary (located 177″ northwest of Regulus in PA 307°) make this pair jump out even in a 3-inch. But all that brilliance gets in the way when it comes to digging out Local Group galaxy Leo I, located 20′ nearly due north of the star.

I don't know the minimum scope size required to tear open this prize, but I suspect you'll need at least a 10-inch. Although I glimpsed the galaxy in my 15-inch at 70× with Regulus in the same field of view, the best strategy was to use a higher magnification (around 150×) to narrow the field and keep the star out of view. Then, I could clearly make out a faint, oval haze using averted vision.

I hope you'll track down a few of these gems in the coming moonless nights and find all the prizes that await your eye.

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Explore the Night with Bob King, Observing
Bob King

About Bob King

Amateur astronomer since childhood and long-time member of the American Association of Variable Star Observers (AAVSO), Bob King also teaches community education astronomy and writes the blog Astro Bob. The universe invites us on an adventure every single night. All we need do is look up. My book "Night Sky with the Naked Eye" was just published and is now available on Amazon and BN. It covers all the great things you can see at night with just your eyeballs. No equipment needed!

8 thoughts on “Hidden Gems in Common Deep-Sky Objects

  1. Rusty

    Hi Bob,

    This is a very enjoyable article you’ve written, Bob. Some of these I’ve seen in the past. Others I’ll have to explore. When I saw the last one, a galaxy near Regulus, I thought you were referring to a similar pair – that is Beta Andromedae and NGC 404, sometimes called Mirach’s Ghost. I’ve seen this little 10th magnitude galaxy with both my 8-inch Newtonian and 11-inch Schmidt-cassegrain. The M46/NGC 2438 pair is one of my favorites. I’ll have to take another look at the Tau CMa open cluster as well. Thanks for these reminders.

  2. Will YoungWill Young

    Great article! Thanks for adding the Smiling Cyclops in the mix! Clayton Jeter is a great friend of mine but he didn’t help discover this one I’m afraid. He did interview me in the Houston Astronomical Societies newsletter about it and was one of the first people I showed for sure. I can see where that might have confused things a bit. Just thought I’d clear that up a bit. Thanks again for adding it to your list! Clear skies!

    Will

  3. Graham-Wolf

    Great work, Bob. Keep it up!

    Must have a gaze at a few of these celestial “gems” of yours, when I have a spare moment.
    The deep-sky afficianados will be most impressed…. and so they should be.
    Aperture isn’t everything, but it sure helps.

    I’m a good-old-southern boy, so the Cross, Omega Centauri, Jewelbox Cluster, Tarantula Nebula, LMC, SMC etc will always be my faves. You’ll need to get yourself down to southern Florida to see those, Bob. But at least we can both admire M45:- the mighty Pleiades!

    Regards from 46 South, NZ.
    Graham W. Wolf.

    1. Bob KingBob King Post author

      Graham-Wolf,

      I’ve viewed a few of those choice southern objects from Tucson, the Caribbean and even Arequipa, Peru but only in small scopes. Still, they’re beauties. I really liked Omega!

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