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Log, Sep 29, 2006

25 people. If you had looked out at noon around here, you wouldn't have given much chance that we'd have a halfway decent night at the Observatory but by sunset the sky was almost cloudless. The Moon was just a bit shy of being a half moon and was fairly low in the southwestern sky where it set by 10:30. Yes, I know all the old hoary stories about the Moon obscuring this or that beautiful object - and they are mostly true. Heck, I've been known to tell a few of them myself. Yet the Moon is a favorite of the grade school crowd, and if the truth be told, it really is a spectacular site. We concentrated on a somewhat obscure crater called Albategnius which was just sunward of the terminator line. Albategnius was named after Muhammad al Bettani, a ninth century Arabian astronomer. Placed as it was with the light at a sharp angle, it stood up in wonderful relief. Albategnius has a very prominent eject mass marking where the meteor which formed the crater hit. Just at the edge of Albategnius, a smaller crater formed later called Klein forms a similar circle and smaller ejecta mass. The two more famous craters Ptolemaeus and Hipparchus form a "triangle" of large craters near the center line of the Moon's near face.

Triangles seemed to form the theme for tonight - but strictly by chance. We spent a good deal of time in Triangulum. We star hopped around the Summer Triangle and we looked a great deal at M33 called the Pinwheel but also called the Triangulum Galaxy. The Pinwheel is the third largest galaxy in the so called local group of galaxies which are dominated by M31 (Andromeda) and our own Milky Way Galaxy [MWG]. After M33, the rest of the local group are either tiny (like the tiny M110 which appears as a knot in M31) or irregulars like the Magellanic Clouds or the Sagittarius Galaxy.

We looked at the Lagoon (M54) but the Moon wiped out most of the nebulosity. We looked at M54, a globular cluster which appears to have originated in the Sagittarius Galaxy but has now been torn away and is beginning to orbit the MWG. M54 is interesting if you know its probable history but frankly it is small and not to distinguished. In contrast, M13, the Great Cluster in Hercules is one of the two most spectacular clusters in the sky (along with the Omega Cluster) and one of the five or six most spectacular objects in the sky. While we were in Hercules, I think it was Ernie who suggested we look at NGC6210 a bluish planetary nebula in Hercules. It is small but surprisingly bright which helped because the Moon was still up. A question came from the visitors asking how these nebulae emit light. The answer is that the central core store which has had some of its atmosphere stripped away to form the cloud emits a large amount of ultraviolet light which raises the atoms of the nebulae from "ground state" to a point where they release light as they try to regain ground state. In a sense they are like neon lights except that it is largely hydrogen which shines.

While we were in the area of the Great Cluster in Hercules, I like to look at three pairs of double stars which are close by in Hercules [Her] and Coronae Borealis (Northern Crown) [CrB]. To get everybody in the swing of things, we start with Sigma CrB which is a widely spaced double star with two nearly equally bright blue white stars. Sigma CrB is close - only about 71 light years away. Its two members are widely spaced. Once everyone has learned how to look at double stars, I point at the nearby Zeta Her which is again two blue white stars, one a very bright second magnitude and the other a dimmer fifth magnitude star. Unlike Sigma CrB, Zeta Her is very closely spaced. Zeta Her is about twice as close as Sigma CrB at 35 light years. Finally I targeted Nu CrB which is an optical double and very much unlike either Zeta Her or Sigma CrB. First of all Nu CrB is really two independent stars that are moving in parallel tracks but widely spaced. In fact, Nu1 CrB is almost as far from Nu2 CrB as we are from Zeta Her (about 33 light years). In spite of being independent, both these stars were probably born in the same cloud of gas at about the same time. Both are growing old together and will expire as supernovae in the next million or two years. They are much farther from Earth than the other doubles (at 522 and 554 lightyears).

Ernie suggested we look at a series of objects. It always impresses me that Ernie has an almost encyclopedic knowledge of galaxies, nebulae, and planetaries by NGC number. I can't remember any of them by number although sometimes names like the Sculptor Galaxy ring a bell. To Ernie, the Sculptor or the Silver Dollar Galaxy is NGC253. We also visited an open cluster in Andromeda (NGC752), the Double Cluster in Perseus and NGC891 which is in Andromeda a bit farther from Triangulum than NGC253.

We visited the Ring Nebula (I at least remember M57 but I'll bet few of us would call NGC6720!). It was ok but the instability of the air as the Moon finally set was obvious. Whenever we targeted a star now, we were treated (mistreated?) to a dazzlingly fractal display of color. Vega looked like shards of broken glass at the bottom of a pool of water.

It was getting late, but a few of us decided to push on. Our next targets were Uranus and Neptune (Pluto, of course, is now a forbidden object because it is no longer a planet). Both presented a fairly steady disk and Uranus at least took fairly high power (300+ diameters). We managed glimpses of one and probably three moons (Titania (almost certain), Oberon (just possibly) both at Uranus and Triton (very likely) at Neptune).

All three moons are between the 13th and 14th magnitudes - well within our scope's ability on a calm night but a real challenge when Vega looks like a stain glass window. So all told we certainly saw 5 moons (Moon, Io, Europa, Ganymede, and Callisto), probably Titania and Triton and just possibly Oberon for a total of 7 or 8 moons in a night. Had we been able to see Saturn we might have pushed our total as high as 12 or 13 in a night. For everyone's information, over the years we have seen a total of 21 moon's at FDO.

-Les Coleman

Leslie Coleman
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Leslie Coleman
Entry Date:
Sep 29, 2006
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Leslie Coleman's Log
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