184 km diameter asteroid occults a 12th magnitude star

There was an opportunity to make an interesting observation when the 184 km diameter asteroid (241) Germania passed in front of (occulted) an 11.8 magnitude star in Gemini on Friday April 18 at 20:59 UT (21:59 BST) as seen from the UK and northern Europe. The maximum length of disappearance of the star was predicted to be 8.5 seconds for someone in the centre of the shadow.

Four observers in the UK successfully monitored the event by video and CCD (Peter Birtwhistle, Tim Haymes, Alex Pratt and John Talbot) with Alex Pratt (Leeds) obtaining the only positive UK observation since he was close to the centre line with fair weather. Peter, Tim and John observed from south of the shadow track and each recorded a ‘miss’ from their location.

Three continental European observers (Jan Marten Winkel and Harrie Rutten in the Netherlands and Gerhard Dangl in Austria) also recorded positive observations with a ‘miss’ noted by H. Bulder, also in the Netherlands.

Results can be seen on the Euraster website www.euraster.net. The four chords (see the diagram) indicate the time periods when the star was occulted. This profile is based on the occultation durations and the geographical position of the observers, from their reports. The asteroid profile was generated with Occult 4 software and is preliminary.


The calculated dimensions of the asteroid from these observations are 185±6 x 171±15 km which is in agreement with previous results of 184 km, and there was a path shift of about 50 km to the NE, with the occultation occurring about 9 seconds earlier than predicted.

For more information on asteroidal occultations and how you can join in this fascinating and exciting observing programme, please see http://britastro.org/asteroids/Occultations.htm.

Tim Haymes, Assistant Director (Occultations)
Asteroids and Remote Planets Section

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