The Official Publication of the Bucks-Mont Astronomical Association, Inc
©2001 BMAA, Inc
BMAA member Bruce Collier provided these images taken at Hickory Run State Park on July 20, 2001
At left is NGC7000S, above is Comet S
- photos by Bruce Collier
At the September General Meeting, BMAA President Ed Murray appointed Paul Kohler as Nominations Chair for the Election of Officers for 2002. Paul has announced that the existing slate of officers has agreed to run again, and that no other members have expressed a desire to do so. The election is normally held at the October General Meeting and any member interested in running may be nominated from the floor.
Wednesday, October 3 at 8:00p - BMAA General Meeting at Peace Valley
The next BMAA General Meeting is scheduled for Wednesday, November 7 at 8:00p
BMAA MESSAGELINE - 215/579-9973
The CONSTELLATION is the official publication of the Bucks-Mont Astronomical Association, Inc, a 501(c)3 non-profit organization incorporated in the Commonwealth of Pennsylvania and exists for the exchange of ideas, news, information and publicity among the BMAA membership, as well as the amateur astronomy community at large. The views expressed are not necessarily those of BMAA, but of the contributors and are edited to fit within the format and confines of the publication. Unsolicited articles relevant to astronomy are welcomed and may be submitted to the Editor.
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2001 Calendar of Events
StarWatch Chairman: Antoine Pharamond, 215/412-9291 email@example.com
Information Line - 215/579-9973
2001 BMAA Officers
President - Ed Murray, 215/493-2843 firstname.lastname@example.org
Vice President - Antoine Pharamond, 215/412-9291 email@example.com
Treasurer - Ed Radomski, 215/822-8312 firstname.lastname@example.org
Secretary - Ken Wieland, 215/362-7228 email@example.com
- photo by Bruce Collier
Andromeda, photographed from Hickory Run State Park on July 20, 2001
Meet the Aberrators VI: Chromatic Aberration
- by John C Deitz and Cor Berrevoets
- The following images were omitted from this article in the September 2001 issue of the CONSTELLATION (Vol XVI, No 9).
This editor regrets the error. [ -ed]
The Planetaries of September and observing them from the city
- by Bernie Kosher
Bear with me in a moment of silence...thank you.
As you know, that old rascal Ach has departed, and asked that I take over to fill the pages of the Constellation with other drivel.
Stella-Della is coming up very soon, so this is being written to encourage you to try some new and not too difficult targets. The skies from Ottsville are a bit bright at lower altitudes, but overhead can be spectacular for this area. Many nights the limit is down around mag 6. If it encourages anyone, last year I tracked down a 12.8 magnitude planetary with a 4.5" scope.
I have always enjoyed tracking down the planetary nebulae. Many are readily visible from light polluted city sites. Some are thin mists and require dark skies and long searches. My primary scope is a 4.5" refractor, which is the instrument in use unless otherwise noted.
Since I frequently observe with Bruce Collier, I find myself yelling over to him "Hey! I can't find NGC ****. Can you take a minute and crank it up for me?" And herein lies the rub.
I dislike reading what an object should look like before going after it. Many is the time I've searched for a half hour or so, only to give up. With the small aperture scopes, many of these are beyond the light grasp, and many are so small they're next to impossible to differentiate from the stars. So with Bruce's 18" and digital setting circles, he can usually at least see the target. Imagine me looking for a 14th magnitude planetary that's only 2 arcseconds in diameter with a small aperture.
However, I spent time seeing many things in my searches that made it worthwhile. There were double stars, red stars and cascades; clusters large and small; perhaps a faint smudge of light.
Back to the subject.
The planetaries are the outer atmosphere of stars just past the red giant stage, blown off during the star's core shrinking to a highly compressed dwarf. Although the central stars of most planetaries are only about the absolute magnitude of the sun, they emit vast amounts of ultraviolet due to their extremely high temperatures, ranging up to about 100,000 degrees. The UV causes the rarefied gases to glow by fluorescence. The electrons are knocked into higher energy states, and when the electrons cascade back to lower levels the energy is emitted.
Due to the extreme rarefaction of the atoms, better than the best lab vacuum, some of the electrons can remain in an energy state which is called 'metastable' for several seconds. Normally, in a gas at any pressure above the levels in the planetary, the electrons would be knocked to a different level very quickly. But in the planetaries' rarefied cloud of gas, the metastable state electrons can jump directly to a lower level, producing the 'forbidden lines' which cause the greenish blue glow so characteristic of these objects. For a more complete and precise explanation, see the literature on the subject. I am hardly an expert and just outlined what is going on.
And now some amateur level observations.
From the outskirts of Trenton, I occasionally get nights when 5th magnitude stars are visible directly overhead. On an average night, about 4th would be the limit. And as is usual in our light polluted skies, much of my area is so light polluted 1st magnitude is about the limit near the horizons.
But wait! One must take advantage of those nights when about any observation is possible, so here's some things to shoot for, all of which I have found from the suburbs with the 4.5".
Cygnus goes directly overhead in September, and is chock full of goodies. The Milky Way runs through, and the galactic plane is the place to search for planetaries and clusters, while the galaxies are rare, and dimmed by the vast dust clouds which are responsible for the 'zone of avoidance.' Sadly, the dark nebulas are hard to discern in any light pollution.
If one pictures Cygnus as a cross, with Deneb as the tip of the shorter, and Albireo as the tip of the longer upright, then the star Delta (itself a fairly close, uneven double, difficult in the 4.5 unless the air is steady) is the tip of the northern side of the arm and Epsilon the southern.
On the northern side is the planetary NGC 6826 (19H43M +50) at mag 8.8 and about 30 by 20 seconds in diameter. This is a 'blinking' planetary, meaning the central star is readily visible if looked at directly, while the surrounding nebulosity is subdued, but the star becomes swamped in the nebulosity if viewed with averted vision. This object is noticeably bluish even in small scopes, and very much so in larger ones. It is located with some hopping and careful examination. Since it is so small, a power of about 50 or 60 is needed to make the planetary look like an out of focus star. I see no real detail other than the central star with my scope. I'd rate the difficulty as medium, but easy once found.
On the other side of Deneb is the slightly fainter NGC 7027, looking much the same as the prior, but with no central star readily discerned. Located at 21H05M +42, this nebula is only about 4 degrees from the Florida coast of the North American Nebula, NGC 7000 (not even suspected from my location) and about three degrees due south of Zeta. Magnitude is listed as 10, and size is 18 by 12 seconds. Somewhat more difficult than the prior. The center appears slightly darker to me, although this may be a contrast thing. Noticeably elliptical.
In Andromeda, actually directly above Pegasus, is the "Blue Snowball", NGC 7662. Located at 23H23M +42.2, magnitude 8.9, size 36 by 30 seconds. Very bright and bluish, but can be tough to locate in poor skies unless the stars Kappa, Lambda and Psi are visible. This nebula shows a bit of detail at higher powers, a sort of folded effect.
In Hercules is NGC 6210 at magnitude 9.7 size 24 by 18, very similar to the foregoing ones. Harder to locate due to it's distance from any nearby bright star, and requiring slightly higher power to make it obvious, this planetary sometimes takes me a few minutes to locate if showing it to someone.
In Draco is NGC 6543, mag 8.6, size 24 by 18. This was one of the first planetaries I went searching for years ago, and I must have passed over it a dozen times. I was looking for a large puffball like the familiar Messier planetaries and not a small bright starlike object. Once found, it is easy, and I have gone to it many times as an example to beginners of how many of the NGC objects are actually easier than some of Messier's. I believe this is called the "Cat's Eye Nebula". In photos with larger scopes, there appears to be several loops intertwined.
Of course, you can stick with the obvious Ring Nebula (M57) and Dumbbell (M27) for the rest of your life. That's OK too.
By far the toughest from Trenton is M76, the Little Dumbbell in Perseus. If you can find this from any kind of light polluted sky, I congratulate you. It's a tribute to Messier's diligence and dark skies that he ever found this little guy.
You'll have to wait until later in the evening for M76.
Well, here's some targets outside the Messier objects which about anyone can do. If you have a scope above three inches these objects should be available. An eight-inch will show them from about any sky when they are high. From the dark skies of Hickory Run many more are easily visible in the Cygnus/ Aquilla/ Sagittarius area.
Good luck! And don't give up. It's very rewarding when you finally locate one of these elusive little puffballs. Not many amateurs seem to get beyond the brighter objects, and eventually lose interest. Sadly, they have not tried just a bit harder.
Oh. I should apologize for giving the locations of some crudely and others not at all. Now how about that? Guess you'll have to look them up.
* * * * * * *
BMAA member Bernie Kosher has been providing 'Tips' for the CONSTELLATION and will now concentrate on 'Observing'.
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