Tuesday, January 01, 2008

Getting oriented in the night sky with Orion

Session Name: 20071229.1940

Click picture for larger image or here for unmarked image.
This image was taken at 12:40AM on 30 Dec 2007.

For a cold December evening and the last observing session for the year, it turned out to be okay in the sky and on the ground. More familiar faces stopped by then newcomers. Kin and I would observe with Hawaiian George, Stan & Gee, and Carol & Doggie. Later Time's Up stopped by. They left just as John and his dog Spencer stopped to spend the rest of the observing session. Mars was the highlight object for the evening, but some naked eye viewing of constellations and brighter open clusters were part of the program. Comet 8P/Tuttle was another primary object sought but ultimately went undetected.

Orion, The Hunter, is one of the most conspicuous constellations in the urban sky. When one locates Orion a host of interesting objects are nearby. These can be had with the naked eye (depending how keen), binoculars, and telescopes.

At this time of the year around 7:30 ~ 8:00, look toward manhattan-east spying for three equally bright and equally spaced stars that form Orion's belt. At the hour described Orion's belt will be almost vertical in the sky. On our Manhattan sky, one should be able to see the brighter members that figure Orion's body, an hour glass shape where the Orion's belt is the pinched center between the pair of bright stars, Saiph & Rigel, that make up his feet towards your left and the other pair of bright stars, Betelgeuse & Bellatrix, that make up his shoulders towards your right. A keen naked eye will detect two or three stars of the Orion's sword, the middle one appearing sort of fuzzy, unfocused.

When Orion is rising, he is leaning backward, where the Betelgeuse lies to the left & Rigel lies lower in the sky to the right of a vertically-oriented belt; at culmination, Orion stands straight up with horizontally-oriented belt, Betelgeuse to the upper left and Rigel lower right (similar to photograph above); lastly, when Orion sets he falls forward maintaining a horizontally-oriented belt, Rigel will fall below the western horizon first.

The marked up illustration describes Orion's Sword with a cartoon insert for detail. When Time's Up arrived this evening, Rich with 3 or 4 other riders, this was the first object shown in the scope at magnification 98x and a true field of view of ~50 arc minutes, about 8/10 of a degree. Using a Thousand Oaks Oxygen-3 (OIII) filter filter, the nebula was stunning. The central density was thick and texturized with undulating grades of brightness; averted vision extends the periphery out to greater distance and enhances the shape of an already interesting "bat" shape.

While some are waiting for a chance at the eyepiece, Mars is pointed out as the brightest object following a rough line from Orion's Belt through Betelguese into the territory of Taurus's constellation boundary. It wasn't too long ago that Mars was in Gemini and having just crossed the boundary. Earth had caught up to and now has passed this red planet in our laps around the Sun. In another 2 and half years, Earth and Mars will once again be nearby within their respective orbits.

Returning to Orion's Belt, our outstretched fingers arced upward to our right to the bright reddish star, Aldebaran. Letting our eyes adjust, the large open cluster shaped like an arrowhead begins to resolve. This is Hyades not too far from Orion's Shield. It is not cataloged as a Messier object, however, one will find as #25 in Melotte's catalog and #50 in Collinder's. Though Aldebaran appears to be a member of the cluster because of its visual proximity, in truth it is not. Aldebaran shines from a nearby 65 light years, whereas Hyades fills a volume of sky and share a common motion some 150 light years distant.

Continuing the line from Orion's Belt past the Hyades, a twinkling array of stars is seen. Some see 3 at first and others can pick out 6 fairly quickly. This is the open cluster, Messier 45 (M45) in Taurus. Legend has it that these are the seven sisters that Orion chases across the sky.

Observing Mars in the telescope at magnification 182x and a true field of view of ~46 arc minutes, a little shy of half of one degree, one could see surface details. Early in the session we could see a dark feature crossing the disk as a chord from an 11 o'clock - 3 o'clock line. Inverted by the scope, this corresponds to maria features above the southern polar cap: Mare Sirenum, Mare Cimmerium, Mare Tyrrhenum. Later in the session around when Mars rose substantially in the sky and the sky conditions improved, some phenomenal views were available. At this time, around 12:30, Syrtis Major had turned on to the disk. Above in the field of view, Hellas's form was observed, especially with the contrasting surrounding maria, Mare Hadriaticum to the west, Iapygia to the north and Mare Australe to the East. At the opposite side, Mare Boreum collared the northern polar cap. In contrast to nothing spotted at the south pole, one could easily see the whitish polar cap inside of the Mare Boreum. Lastly, a faint darkening feature was detected in an area corresponding to Elysium and Stymphalius Lacus. At this time, I am not certain what feature was observed.

For variety of character, the scope was turned from Mars to nearby M35, an open cluster at the feet of Gemini.

During the session, Kin and I looked for Comet 8P/Tuttle with no success. With the ephemerides we had on hand, we located the starfield but couldn't sense the comet in binoculars or with the telescope.

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