October's Comet: Hartley 2

October offers opportunities to observe comet 103P/Hartley 2 bieten. Hartley 2, a small Jupiter family comet, will pass its perihelion on October 28. That will be 8 days after closest approach to the Earth at a distance of just over 18 million kilometres on October 20.

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The above diagram of the comet's orbit shows that we can observe Hartley 2 at night throughout October. Every evening it will rise a bit later; the time of its culmination shifts to the early morning hours. The comet's orbit reaches out all the way to Jupiter, so its orbital energy is a lot higher than the Earth's and its perihelion velocity far exceeds the Earth's orbit speed. The comet is swiftly overtaking us. 

Due to the orbital inclination the maximum elevation from northerly latitudes continuously decreases. Observers at southerly locations are better off in this respect, but they too will have to get up in the wee hours. This is an inevitable consequence of the relative positions of the Sun, the Earth and the comet.  

After October 28 the Earth and Sun range will increase rapidly as the comet speeds away on its highly eccentric orbit. 

Here is a PDF file with a sky chart produced by Andreas Schnabel showing Hartley 2's path through the constellations.

This table shows the right ascension and declination at 20:00 GMT (22:00 CEST or 21:00 CET) and the constellation which Hartley 2 will be traversing: in the time frame regarded here, these are Perseus, Auriga and Gemini. To obtain the exact ephemeris for any other time from your precise location, please use JPL Horizons:

Next Stop: EPOXI

Before Hartley 2 disappears towards its aphelion, it will be encountered on November 4, 2010 by the NASA spacecraft EPOXI. EPOXI originally was the carrier craft of the highly successful "Deep Impact" mission to comet 9P/Tempel 1 in 2005. After the Tempel 1 encounter the spacecraft was still fully functional with plenty of propellant remaining in its tanks, so it was renamed and retargeted for the Hartley 2 encounter. On November 4 EPOXI will pass Hartley 2's nucleus at only 700 km distance. Doesn't this remind you of the European Space Agency's GIOTTO spacecraft, which flew past comet 1P/Halley at a distance of only 600 km on March 13, 1986?

... and a Word of Caution!

Comet 103P/Hartley 2 taken from Darmstadt, Germany by Gunnar Glitscher, AAW-Darmstadt in the early morning hours of October 18, 2010. Focal length 80 mm, two images with 30 seconds exposure duration each

Don't expect anything impressive like Hale Bopp in 1997 or McNaught in 2007! Hartley 2 is a lot smaller comet and chances are, all you'll see is a vaguely greenish blob. That is what you get if a comet is really close. Still, this comet is passing in front of numerous interesting sites and it's fascinating to watch this visitor from the outer solar system that might very well have ended up on an impact trajectory - in fact, it still might, if Jupiter's gravity happens tweaks the comet's orbit just a bit at some point in the future. I was out with my friends from the astronomy club on both Friday and Saturday night and I admit I was a bit ... underwhelmed. Well, we did benefit from the clear sky and good seeing to shoot a series of pix that should turn out quite well once we've stacked them. 

Further Information

JPL Horizons web interface for the computation of exact ephemeris data for astronomical observations

103P/Hartley 2 in the NASA JPL small body database - though the orbital elements given there are not accurate enough to reproduce the current orbital stateand the ephemeris for observations

Coarse and fine finder charts for 103P/Hartley 2 on heavens-above.com

Make sure you check out spaceweather.com for up-to-date information on the observation status. This web site also recently posted some really great telescope images of Hartley 2 such as the one to the right (click on it for a larger version).

 

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