Motion of Comet Wirtanen near Aphelion

The faint, moving image of the nucleus of Comet Wirtanen (in the circles), as observed by the 8.2-m VLT KUEYEN telescope (formerly UT2) and the VLT Test Camera on May 17, 1999, during the commissioning phase. The telescope followed the comet's motion and the stellar images in the field are therefore seen as trails. Each exposure lasted 8 min through a red (R) filtre. The brightness of the comet is less than R = 25 magnitude, or over 50 million times fainter than what can be seen with the unaided eye. The field of view measures about 17 x 15 arcsec 2. North is up and east is left.

These images were taken on May 17, 1999, between 06:50 and 09:50 UT with the VLT Test Camera at the KUEYEN telescope (VLT UT2) at the Paranal Observatory (Chile). The individual images were bias-subtracted, flat-fielded, cleaned of cosmics (dark pixels caused by cosmic rays impacting on the CCD detector) and normalized. The best twelve images were selected, aligned to the same pixel position and coadded. The observing conditions were variable; the seeing was initially about 0.4 arcsec, but deteriorated somewhat during the observations.