Cygnificant celestial sighting

Just a while ago I ventured outdoors with a pair of binoculars and had a look at Comet SWAN, which presently has an apparent magnitude of ~6.5 to 6.8 — just too faint for normal people to see with the unaided eye — and appears in the constellation Bootes.

Officially designated C/2006 M4, SWAN — named after an instrument on board the Solar and Heliospheric Observatory (SOHO) spacecraft — was discovered less than four months ago. If you want to see it, grab some field glasses and, using the diagram at right, follow a line passing through Alioth (the second of the four stars in the Big Dipper’s handle) and Alkaid (the star at the end) toward Bootes, which looks like a necktie. Segenus, the star nearest the Big Dipper in the fat part of the tie — which to some wildly imaginative bedouin apparently represented a hunter’s shoulder — is your reference point. (Arcturus, the red giant star found at the knot of the tie, is the third-brightest in the sky.) If you visualize Bootes as balancing on its knot, SWAN is just below and to the right of Segenus, enclosed in an almost-equilateral triangle of similarly dim stars.

SWAN is one of many comets with a hyperbolic orbit, meaning that its passage really is a swan song. As playing with the applet at the JPL site reveals, SWAN passed the apex of its orbit at the beginning of October and is now headed out of the solar system. Its closest passage to Earth, about 90 million miles, will take place about 10 days from now.

  1. #1 by JanieBelle and Kate on October 17, 2006 - 8:19 am

    Just a small correction.
    and appears in the constellation Bootes.
    We all knew what you meant, though.

  2. #2 by Kevin Beck on October 17, 2006 - 11:26 am

    You know, something didn’t quite look right even after I read through this post 10 times before hitting “Publish Post.” Thanks, JB&K. In my own meager defense, Bootes is kind of comet-shaped, though. Kind of.

  3. #3 by Jim on October 17, 2006 - 11:36 am

    It seems a line between Alkaid and Mizar is closer to what’s been drawn. From the end, the sequence is Alkaid, Mizar, Alioth. (I don’t know very many star names but Mizar I’m familiar with via the double star “eye test”. That, and the fact that a planet circling Mizar was a key element in an old Steely Dan tune from Royal Scam.)

  4. #4 by Kevin Beck on October 17, 2006 - 1:13 pm

    Jim — I should have used a better graphic. The line in the one I used is irrelevant to the comet as it points to Arcturus, ordinarily best found by using the “follow the curve of the dipper handle” rule. This is one of the few occasions in the history of astronomy that keeping a watch on a sixth-magnitude object has taken precedence over pinpointing α Botis.
    Had notable stars been named in the 20th and 21st centuries, instead of Algol, Fomalhaut and Procyon, they’d have identifiers such as Zoloft, Remeron and Midol.

  5. #5 by Jim on October 17, 2006 - 1:19 pm

    Never mind. Upon rereading I see that the line is to bring you to Segenus, not through SWAN (which I assume is where Alkaid-Mizar would bring you based on the description).

  6. #6 by Jim on October 17, 2006 - 1:21 pm

    I see we have cross posted. How (un)timely of me! In any case, just where would this star “Midol” be located? In the constellation “Cramps” by chance?

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