University Lowbrow Astronomers

Doug’s Deep Sky Challenge—An Egg Hunt in Cygnus.

by Doug Scobel
Printed in Reflections: June, 2012.

To appreciate this story, you have to set your wayback machine to 2007. That year I attended the Okie-Tex Star Party along with Mark Deprest, Robert Wade, and Nathan Murphy. Okie-Tex is a truly remarkable star party that boasts some of the darkest skies found anywhere in the continental United States .

 

I won’t go into much detail on the ‘07 OTSP, but if you are curious you can read about it here: http://www.umich.edu/~lowbrows/reflections/2007/dscobel.28.html

 

So on to the egg hunt. Nathan decided one night that he’d choose a page of the Pocket Sky Atlas and see what he could see on it. Now I couldn’t read his mind, but I’m sure that his thought process went something like this: “Let’s see, what’s up high right now? Hmm, Cygnus is nearly directly overhead, but I have the 10-inch Portaball, so there’s no such thing as Dobson’s Hole with that scope. Yeah, let’s try Cygnus.” So he opens the PSA to Cygnus, and continues. “Let’s see, here’s a nice looking planetary, the ‘Egg Nebula’. Hmm, if it’s in the PSA, it must be relatively easy, especially considering I’m under the darkest skies in the country, and I have a ten-inch scope. How hard can it be?” How hard can it be? Plenty hard as it turned out. Half an hour later, I’m sure Nathan is thinking thoughts that I cannot share here. Let’s just say that he was very frustrated at not being able to find something that “ought to be easy”. In desperation he turns to the rest of us to enlist our help. I look at the page in PSA. “Looks like it should be a nice little planetary” I think to myself. “OK, how hard can it be?” I line up the Telrad, and look though my trusty old 13” Dob named Papa Smurf. Nothing. Pan around some. Nothing. Get out the oxygen-III filter and blink it in and out. Still nothing. Pan around some, go back to the starting point, blink the O-III in and out, pan some more, blink, pan, start over, etc., etc., etc. Still nothing. What the heck? OK, time to get out the big gun, Millennium Star Atlas. Find the chart, there it is, try again. Nothing. OK, go back to Millennium Star Atlas. There’s a little pentagon-shaped asterism, and the nebula is on one of the five sides of the pentagon. Find the pentagon, find the nebula. Back to the scope and pan around the dense star field in Cygnus, which is already dense because the Milky Way runs right through it, but is rendered even more so because of the extremely dark sky. “Dang, there are a lot of stars up there!” After a good 20 minutes, I finally find the little pentagon in a low-power, wide-field eyepiece. “The nebula should be right there. Where is it?” Blink the O-III in and out. STILL NOTHING! WHAT IS GOING ON?” Everything dims equally and there’s no sign of a nebula. All I see is a close, dim, double star where the nebula ought to be. “OK, let’s zoom in.” At higher magnification the confounded egg finally reveals itself! The close, dim, double star is actually enveloped in nebulosity. Finally, success, if you call finding an object after an hour’s worth of searching “success”. Since that time we’ve unaffectionately referred to the Egg Nebula as Nathan’s Nemesis and Murphy’s Bane, which are certainly more descriptive names based on our experience. That sure was one tough little bugger! But we found it.

 

Nathan Edgy

At the 2007 OTSP, Nathan looks to be a little edgy after wrestling with the Egg Nebula last night. Guess who won.

 

Okay, back to the present. We’re at CLEAR IV in Atlanta, MI, the weekend of May 18-19 of this year. During the second night, Yasu suggests that we look for the Egg Nebula. “NO WAY” Nathan and I reply almost in unison. I’m not doing that again — that was not fun. Then I start thinking about it. I think to myself “You know, I do have a 16-inch scope now, the skies are really dark, and I sort of remember how to find it. Cygnus isn’t too high yet, so Dobson’s Hole shouldn’t be a problem. Find that little pentagon and I find the nebula. How hard can it be?” Yeah, how hard can it be? Plenty! Of course, I have to dig out Millennium Star Atlas, but I forget that the elusive Egg does not respond to O-III filters like normal planetaries do. Despite all that, after “only” a half hour’s worth of searching this time, I find it. “Hey Yasu, I found it!” Someone replies “He went to bed”. “Great, all that work and he goes to bed and I can’t show it to him. I’ll have to have a word or two with that guy in the morning” I mutter to myself.

 

Despite Yasu not being available to see it, this story has a silver lining. I now know a sure-fire way to star-hop to it quickly, and I think you can do it too. Even from less than perfect skies.

 

Start with the Pocket Sky Atlas, chart number 62, or virtually any other star atlas, or just Chart 1 shown here. Put your Telrad midway on a line between magnitude 3.7 Tau Cygni and magnitude 2.5 Epsilon Cygni. Now adjust your scope so that the Telrad’s bull’s-eye is just a smidge north of the midpoint of the line. Now look in the lowest power eyepiece you have. Near the center of the field you should be able to easily find the double star Yale BSC 8051 (BSC = Bright Star Catalog), whose components are separated by about 1.2 arc-minutes and are of magnitudes 6.0 and 8.7. Chart 1 shows where to put the Telrad circle.

 

Chart shows where to place the Telrad circle

Chart 1. This chart shows where to place the Telrad circle, between Tau and Epsilon Cygni. North is at the top and east is to the left. Chart was generated using Guide 8.0.

 

That double star comprises the southernmost corner of a trapezoid of stars that is angled roughly NNE to SSW, about 9 arc minutes on the longest (SE) side and six arc minutes on the shortest (NE and NW) sides. Going clockwise from the brighter double, the star magnitudes are 8.7, 10.0, and 9.8. Chart 2 shows Yale BSC 8051 and the trapezoid near the bottom of the chart.

 

Chart shows the location of the trapezoid north of YBSC 8051

Chart 2. This chart shows the location of the trapezoid north of YBSC 8051, and the pentagon to its north. The location of the Egg Nebula is circled. North is at the top and east is to the left. Chart was generated using Guide 8.0.

 

You should notice that the first star clockwise (to the NNE) from the bright double is itself a double star, with components separated by about 45 arc seconds. These two double stars point almost directly to the nebula, a little more than half a degree to the NNE. But to be sure that you have the correct field, you have to find a pentagon of roughly 8th magnitude stars, with a sixth 8th magnitude star in the middle. This pentagon is much larger than the trapezoid, close to a degree across, and is also shown near the top of Chart 2.

 

Once you find the pentagon, finding the Egg is easy. It’s situated along the southern side of the pentagon, closer to the westernmost star that defines that side. Once you see what appears to be a faint, close, double star, increase the magnification to at least 200x. You should see that the two “stars” are enveloped in nebulosity, and that one of them is slightly brighter than the other. The image below approximates the appearance of the nebula in the eyepiece — but remember that it is much brighter in the image here than it will appear visually.

 

The Egg Nebula, PK80-6.1

The Egg Nebula, PK80-6.1, is at center. Sloan Digital Sky Survey image courtesy the Space Telescope Science Institute.

 

There, you found it! That wasn’t so hard, was it? Maybe I don’t want you to answer that. After all, I haven’t tried using this method locally under our more light-polluted skies. But I intend to try next time I’m out.

 

So what is the Egg Nebula anyway? It’s marked in both Pocket Sky Atlas and Millennium Star Atlas as a planetary nebula, but why does it not respond to an O-III filter? It is thought that the Egg is a proto-planetary nebula. In other words, a star that is in the process of becoming a planetary nebula, but not quite yet. The hypothesis is that it is so early in the process of becoming a planetary nebula that its dusty environment is shining by reflected light which is over-powering any ionized gas emission.

 

Here’s a table with some data on the Egg Nebula. Some sources list it as magnitude 13.5, but from my observations and those of others I’m calling it approximately visual magnitude 11.5 or 12. That sounds faint but its surface brightness is quite high due to its very small angular size.

 

Perek-Kohoutek designation

PK80-6.1

Galactic Nebula designation

GN 21.00.3

Coordinates (epoch 2000)

RA 21h 02m 19s   Dec +36° 41m 38s

Magnitude

~12

Size

~30”

 

So, can you hunt down the elusive Egg? Under pristine skies it should be visible in a six-inch scope, but under the compromised skies of SE Michigan I’m guessing you’ll need at least an eight-inch if not larger. If you have such a scope, then the next time you’re out this summer try doing an Egg hunt in Cygnus. I’d like to know — what do you see?

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Copyright © 2013, the University Lowbrow Astronomers. (The University Lowbrow Astronomers are an amateur astronomy club based in Ann Arbor, Michigan).
This page originally appeared in Reflections of the University Lowbrow Astronomers (the club newsletter).
This page revised Sunday, March 9, 2014 4:30 PM.
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