Friday, November 9, 2007

Surprise comet



(click on the picture to see a larger version)







Figure 1 (from "Sky and Telescope" magazine.)









Photographer AnnMarie Jones
Location Aberllefenni, Wales, UK
Date 5th Nov '07 - pm
Equipment Canon 20D 100-400L @ 400mm Celestron CG5 mount






(click on the picture for a larger version)





Figure 3

These sequential pictures taken by Gary Seronik (RASC)








We have an unanticipated visitor in the night sky right now. I'm talking about the periodic comet Holmes. That comet orbits between Mars and Jupiter (right in the asteroid belt) and is normally very faint - too faint for many telescopes and certainly binoculars. Its orbit is tilted with respect to the plane of the orbits of the major planets and the average plane of the asteroid belt. As a consequence, the comet encounters the asteroid belt twice - once on the way "up" from "below", and again on the way "down" from "above" the planetary plane.

In the last couple of weeks, it has become very bright (relatively speaking), so that it can now be seen with the naked eye, and is certainly quite easy in binoculars. Some people have estimated its brightness at 2nd magnitude, whereas it is normally at 17th magnitude.

In astronomy the magnitude of an object refers to its brightness; each magnitude is approximately 2.5 times brighter than the next. A bright star, for instance, can be of magnitude 1, with larger numbers actually denoting lower brightness. So a star of magnitude 1 is 2.5 times brighter than one of magnitude 2, which in turn is 2.5 times brighter than a star of magnitude 3, etc. You can therefore get a pretty good idea of how much the comet's brightness has increased if you consider that its brightness has increased by about 15 magnitudes (that's 2.5 raised to the 15th power) which comes to approximately a million times. For a more precise explanation, see an article by Nick Strobel.

This brightness increase is unexplained at the moment. My hunch is that the comet collided with some asteroid or a large meteoroid. Something very similar was done artificially by deliberately crashing the "Deep Impact" probe into the comet Tempel 1.

You can find comet Holmes on a clear evening if you look to the northeast at around 8 pm (and it'll be visible all night long, as the sky turns through the hours, slowly making its way to the overhead, and later, northwest position). Make reference to figure 1 to find it in the sky. The comet is in a position in it's orbit which will keep it in the area of the Perseus constellation until about March 2008. Perhaps it'll keep up its brightness - comets are notoriously unpredictable in that regard. Use your binoculars to enhance the view. You'll probably see a fuzzy blob, quite distinct from the nearby stars.

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