Sunday, September 5, 2010

Comet 103/P Hartley

In November of this year,  the EPOXI mission spacecraft will make a close flyby of comet Hartley 2, also known as 103/P Hartley.  The EPOXI name is a combination of EPOCH (Extrasolar Planet Observation and Characterization) and DIXI (Deep Impact eXtended Investigation).  The goal of this flyby is to gather data that will help us understand the structure, formation and composition history of cometary nuclei.  This information is important as it relates directly to our increasing understanding of the origin of our solar system.

This comet is predicted to reach naked eye brightness in late October, perhaps as bright as magnitude 5.  Last night night I decided to see if I could spot the comet in the LX200 12" SCT as it is currently well placed in the constellation Lacerta.  I had downloaded ephemerides for this comet from the IAU (International Astronomical Union) Minor Planet Center which indicated that the comet may currently be as bright as magnitude 8.5.  I was a bit skeptical as I had "googled" this comet and there are not many amateur images out there, suggesting that it is not exactly an interesting target...yet.  Gary Kronk maintains an excellent site called Cometography and there is information on this comet as well as a couple of images if you are interested.

Despite my skepticism (unusual, I know) I slewed the scope over the comets location and saw...nothing.  I decided to completely shut off the dim red lights that were on in the observatory and increase the magnification to 234x to darken the sky background in the eyepiece.  Sure enough, there in the center of the eyepiece was the faint glow of the comet.  My sketch of this comet is at left, and you will probably need to click on it so you can see the full size image.  It was hard to sketch such a faint glow, one that was essentially seen using averted vision.  It was also difficult to ascertain the size of the comet as it was extremely diffuse with no central condensation visible.  I would estimate that this comet is closer to magnitude 10-11, as it has a very low surface brightness...but again, I do not know the extent of the comet, so any estimate of it's magnitude is more of a guess than anything.  I completed this sketch at 0346 UT on 9/5/2010 (which was 8:46 PM MST on 9/4).  I should mention that the sky conditions were excellent with seeing that was estimated at 4/5 and a level of transparency that was as good as it gets from my location on the city's perimeter.  The milky way was visible from Sagittarius through Cygnus and beyond.

After spending some time on the comet I decided to have a look at NGC 40, a planetary nebula in Cepheus, also known as Caldwell 2.  Since I installed the 12" SCT I have been having fun observing planetary nebulas looking for features that were not visible to me with my previously smaller telescopes.  NGC 40 is a wonderful target, one that deserves more popularity.  The 11.6 magnitude central star is visible in most telescopes, and it is surrounded with a large circular shell of nebulosity.   As you know from previous posts, planetary nebula often hold up to greater magnifications without breaking down as other targets do, and NGC 40 was no exception.  I observed NGC 40 using an 8mm Ethos eyepiece, which in the 12" results in  a magnification of 381x and a field of view of .3 degrees.

You can see in the sketch that at high power the nebula is no longer a neat circular haze, rather it has bright arcs on both the east and west sides.  The arc on the west is the brighter of the two, and it seems to arc away from the nebula to the south in a manner reminiscent of a galactic spiral arm.  This planetary nebula is approximately 3500 light years away and spans a diameter of 38 arcseconds.  If you have never observed this target, it is highly recommended.

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