Wednesday, October 31, 2012

A comet

Last night ODI took several images of the comet 168P/Hergenrother. The image shown below is a single exposure in the r' band and covers an area of about 1x1 arcminutes (one OTA cell). 168P is a special case of a comet, as a few days ago a fragment broke off the main body, as can be clearly seen as the fainter spot below the comet. 168P is continues to break apart, and is actively being monitored by various research groups. See, e.g., this JPL press release.

To the right of 168P a streak of a star is visible. Since the comet moves at a different apparent velocity on the sky than the stars, we had to modify the telescope guider to actually follow the comet instead of the stars. Thus the star in the image is trailing. This different apparent movement on sky as compared to the distant background stars is common to all solar system objects (albeit to varying extent), and is a combination of the proper motion of earth itself and the orbit the solar system object.  

We achieved following the comet (called non-sidereal tracking) by modifying the ODI guide module: This module uses the video signal of a bright star to send corrections to the telscope tracking system should a star wander of its ideal position.  For the non-sidereal guiding we added a drift rate to the "ideal" star position, thus constantly pushing the telescope tracking system to follow the comet's motion.

Last night's observations of comet 168P nicely demonstrate that ODI is now fully capable of supporting solar system observations with its non-sidereal guide mode. 


Note added Nov 1st: In this image, west is left, north is up.

Comet 168P, Evening of October 30th MST


  1. Thank you guys so much. We're putting the 2m Faulkes back on this tomorrow, but you've captured the fragmentation event we detected superbly.

    Kind regards

    Nick Howes - Faulkes Telescope Pro-Am Programme Manager

  2. Congratulations on your achievement of this wonderful image! Thank you for sharing it.

  3. A real lucky shot you made! Congrats!
    Andrés Chapman(I-39)