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Small Wonders: Pegasus
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Small Wonders: Pegasus
A Monthly Beginners Guide to the Night Sky
by Tom Trusock
A printable version can be found here.
Wide field Chart
Ah Pegasus -
For naked eye observers, the great square of Pegasus is the dominant feature in northern hemisphere skies in the fall. Ironically, the stars that make up the "Great Square of Pegasus" are not all in Pegasus - the NE star is Alpha Andromedae. Alpha Andromedae was - at one point - shared between the two constellations, but when the official constellation boundaries were drawn up the great square lost one of it's cornerstone to Andromeda - Alpheraz.
No matter - Andromeda is happy to lend it back as needed.
Pegasus covers 1,121 square degrees of sky - the seventh largest constellation overall - yet because of it's position overlooking intergalactic space, for small scope owners, it's relatively devoid of bright objects. It you are lucky enough to own a moderately large scope (8 inches and up), then Pegasus will keep you busy for a very long time.
The winged horse Pegasus is a fairly content creature - especially considering only his front half made it into the night sky - and upside down at that... If you have problems seeing a horse in this constellation, trust me, you won't be alone. But give the following a try. First, if you are in the northern hemisphere, stand on your head. Then reference the picture to the left. Note that south is now up (and should match your inverted view). The green is his neck and head, the red - his body (sans wings) and the blue - his front legs out stretched in full gallop.
Historically, we can trace Pegasus back to the ancient greeks - Pegasus was the offspring of Medusa and sprung from her neck after she was slain by Perseus. And we think sci-fi / fantasy is a "new invention" - Gotta love those ancients...
I first was introduced to the concept of Pegasus as a test for naked eye limiting magnitude (NELM) by Walter Scott Houston (Deep Sky Wonders). Houston notes that by counting the stars visible inside the great square you can determine your limiting magnitude. He writes that at mag 6, you should be able to see 13 stars inside the square. I thought it might be fun to take that a little further. I'd suspect that many readers of this column probably have skies worse than mag six.
Lets take a quick look at the three cornerstones of the Great Square that actually lie in Pegasus. Starting with the SE corner and proceeding counterclockwise around the square we have:
Gamma Pegasi (Algenib) at mag 2.83, it's the third brightest star in the constellation pegasus. Hipparcos satellite data places it at 333.15 light years away. Thus the light you see tonight was leaving this star around 1670. To give you a taste of current events in 1670: The Hudson's bay company was formed, the Kings of England and France met in secret to sign a treaty ending hostilities between their nations (at least for a while), Phosphorus was discovered, Senegal was settled by the French, a Cossack rebellion in the Ukraine was crushed, and Henry Morgan captured Panama.
Alpha Pegasi (Markab or Marchab) is mag 2.49, and is placed at a mere 139 light years away (again Hipparcos) - the closest of the three. This means the photons entering your eyes tonight left around the year 1864. This year saw the continuation of the American civil war, Montana becoming a territory, 70,000 people killed as a cyclone swept through Calcutta, James Clerk Maxwell discovered microwaves, Emil Nobel was killed while experimenting with nitroglycerin, and the birth of both Jacob Astor and Toulouse-Lautrec.
Beta Pegasi (Scheat) is around magnitude 2.4 and lies 199 light years away. In 1804, world events saw the end of French rule in Haiti, the start of the first Barbary War, the first steam locomotive, the Louisiana purchase, the beginning of the Louis and Clark expedition, Boneaparte crown himself emperor (the first emperor of France in 1000 years), Spain declared war on Britain, and the discovery of the asteroid Juno by German astronomer K. L. Harding. Ponder the the state of humanity as you gaze into the past at the deep orange of Scheat this evening.
Astronomy can be your own personal time machine - but these are among the closest targets we will visit tonight. With one exception, the rest of our stops will be in the depths of intergalactic space.
Now without further adieu, let's continue our tour....
NGC 7814 (also Caldwell 43)
First stop lies about two degrees west north west of Gamma Pegasi - the 10.5 magnitude galaxy NGC 7814. While this is a spectacular galaxy in pictures, small scope owners should content themselves with looking for a small tuft of cotton floating in intergalactic space.
If you have a larger scope, be careful that you don't stop at NGC 14. This mag 12 galaxy might confuse you for a minute as it lies almost exactly between 7814 and gamma, but at mag 12.2 (compared to mag 10.8) it's a fair amount dimmer.
While it's been seen in telescopes as small as 4" from very very dark sites (I should note not by yours author - at least of this writing), I find that I usually need something more along the lines of 6-8 inches to pull it out. Ironically, the Night Sky Users Guide lists 7814 as a binocular object. I have my doubts, but must confess I've never actually tried. Perhaps someone out there would be so kind as to let me know the smallest aperture you can grab this faint galaxy through - can you indeed spot it in binoculars? As with all faint galaxies, try to minimize light pollution when searching - even the moon can seriously affect your ability to see it. Once you find it, try alternating between high and low powers and note the results.
One should be aware, that a galaxies listed magnitude is not necessarily the best indicator of it's visibility. The magnitudes listed may actually be, and often are photographic magnitudes; a film emulsion has different sensitivities than the human eye. Additionally, the magnitude describes the brightness of the object as if it were collapsed into a point - like a star. Galaxies have their light spread out over a larger area of the sky. A better indicator of visibility is a galaxies surface brightness - usually measured in magnitudes per square arc second - a brightness per unit area indicator. Still, don't ever let an objects low magnitude or surface brightness ever stop you from looking for it - you just may surprise yourself!
NGC 7479 (also Caldwell 44)
And now onto one of my favorite galaxies in Pegasus - NGC 7479
Continue along the bottom of the great square until you hit Alpha, then move about three degrees south.
This is a very nice barred spiral galaxy, and serves as an excellent example of what larger aperture and darker skies can do - showing a progressive increase in detail with each size.. Smaller scopes should look for a straight wisp of light that may resemble an edge on or lenticular galaxy - larger scopes will begin to show progressively more detail. The view to the left greatly resembles the view through my 18" at ~200x from a dark site - a star like core, an obvious bar, and two well defined arms.
Steven James O'Meara showcases a drawing in The Caldwell Objects that also looks remarkably like the DSS image shown above. Amazingly he was observing with a "lowly" 4" scope. Granted it was from the pristine skies of Hawaii, but still it goes to show just what dark skies (and excellent well trained eyes) can achieve.
NGC 7619 and the Pegasus I Galaxy Cluster
Right off the bat, I'll tell you this target's not really all that fair. It really should have been a challenge object, but I wanted to reserve this months challenge for something special. So don't be dismayed if you don't find it, but if you do - let your mind encompass exactly what you are seeing. This is a fairly loose galaxy cluster located about 250 million light years away. That's right - 7619 is the center of the Pegasus I *galaxy* cluster.
If you look carefully, you may find galaxies scattered across a couple of fields of view, but NGC 7619 (center) and NGC 7626 (left) are two of the brightest members and thus you have the greatest chance of picking them up..
While I've not quite managed them in my 4" scope, my good friend Ron B(ee) has grabbed both of them and one other - NGC 7611. An impressive feat for a 4" scope for sure. Turn as much aperture as you have to this galaxy cluster and see what you can see. Take notes and then compare to the DSS picture above.
Be sure to take time the time to let your eyes fully dark adapt. You might try viewing with your head under a dark towel or sheet to shield all extraneous light, and use averted vision while scanning the field and moving the scope very slowly - (we tend to pick up dim objects slightly better if they appear to be in motion). Who cares what the neighbors think?
I frequently like to start my sessions with a spectacular object like M15, move on to the faint fuzzies, then after my eyes are used to searching for faint targets - finish up with a couple of bright showpieces. After all those dim faint galaxies, M15 comes across as a sensation to the eyes.
From a dark site, M15 is a naked eye object, and an easy catch in almost any size binocular. With my 4" refractor, I find 100x and just under a degree field to be the perfect view. As I increase in aperture, I like to increase power. When I get to larger scopes, I find I'm fond of busting this globular apart with 400 and 500 power!
How much power does it take with your scope before the cluster appears resolved across the face? Does it ever?
M15 contains a hidden prize for the careful observer - it's very own planetary nebula! Pease 1, found in 1928 by Francis Pease, was the first planetary nebula ever discovered in a globular cluster. Pease 1 is so far away it appears stellar at any power in a amateur telescope - the only real way to identify it is to star hop to the location indicated and then pop in an OIII filter. Because Planetary Nebulae are high in OIII, the rest of the stars in the field dim, and the one that remains bright - is the planetary nebula. While most observers who record Pease 1 are looking for it with large aperture (12" and up), there are reports of it being caught with scopes as small as 8". If Pease 1 interests you, then be sure to visit the site listed in "Additional Reading".
NGC 7331 - The Deer Lick Group (also Caldwell 30)
NGC 7331 is without doubt, the dominate member of the "Deer Lick group" - which apparently received it's name in commemoration of an excellent night of observing at Deer Lick Gap just off the Blue Ridge Parkway in the North Carolina mountains.
An easy catch in my 4" scope at 40x, I note "..a fantastic needle that showed some apparent mottling..." with higher powers. While 7331 is spectacular in and of itself with any aperture you throw at it, larger scopes provide more of a glimpse into its surroundings. With sufficient aperture, it becomes a Gulliver surrounded by an army of Lilliputians. When viewed through a 15" scope, I've noted: "This SA(s)b m9.5 galaxy is simply superb... 99x does a wonderful job of framing the galaxy in it's surroundings, and even allows for occasional glimpses of what appears to be a dust lane on the western side. The core itself is non-stellar and perhaps even a bit mottled. Increasing the magnification to 243x darkens the sky further and allows a glimpse of a featureless NGC 7335 and NGC 7337. One should be sure to look for NGC 7336 which can masquerade as a double. It's "companion", a mag 10 star, lies a short distance to the north."
Although it fits easily into any telescope, O'Meara's book - The Caldwell Objects tells us that NGC7331 is among the largest galaxies known. It's diameter (for an accepted distance of 47 million light years) is 130,000 light years, and that it equals in both size and mass the great galaxy in Andromeda - M31.
While it's a fairly bright galaxy, and should be easily picked up by sweeping, it might be a little hard to find the initial area. Fortunately, there's a solution. If you can see Pi and Eta naked eye the imagine the right triangle pictured. 7331 lies right at the 90 degree angle. If you can't see these two stars naked eye, you may wish to start a star hop at beta and "come round the corner" so to speak. Which ever method you choose - don't give up, 7331 is worth the effort.
Although it's a beautiful object in it's own right, 7331 is a jumping off point for our final and challenge object this month.
Challenge Object: 7320 and Stephans Quintet
Stephan's Quintet - 5 galaxies squeezed into 3.5' of sky, Stephan's is on the must view list for any serious deep sky observer.
Unfortunately, the brightest of the bunch - NGC 7320 is also fairly faint - coming in at mag 12.5. From a moderately dark site, I've seen all 5 in a 10" scope, and 7320 should be visible in an even smaller scope under decent skies. The bottom line is, you'll never know till ya try.
While some might think this group a bit much for the typical small scope owner, I've been constantly surprised by communications I've had with various folks - some seem to be hitting the challenge objects with little difficulty - so, I present the following:
Historical events obtained from:
Pease 1 finder charts and observing reports can be found at - Doug Snyder's Planetary Nebula Web Site:
Hubble Pics of Stephan's Quintet
Hipparcos Space Astrometry Mission
The Caldwell Objects - Stephen James O'Meara
The Night Sky Observers Guide - Kepple and Sanner
If you liked this article, be sure to check out the rest of the series.
I'd love to hear of your experiences under the night sky - please feel free to
e-mail me or send any observing reports to: email@example.com
Please indicate if I can cite your observations in future columns.
Photographic Images Courtesy DSS: copyright notice
Star Charts Courtesy Chris Marriott, SkyMap Pro 10 used with permission