[BAA 00336] Rare asteroid occultation of a naked eye star

[Rick]

( ...if anyone's going to be in Scotland next Friday evening... )

BAA electronic bulletin No. 00336 -- http://www.britastro.org/

On Friday night, 2008 April 11, at around 20:49:30 UT (21:49:30 BST), the 20km asteroid (1886) Lowell is predicted to occult the naked eye star 4.8 magnitude HIP 63355 (36 Comae Berenices).

The latest update (March 28) shows the shadow track crossing from east to west almost centrally over Edinburgh, Glasgow and surrounding towns.  The star will be at an elevation of about 38º, in azimuth 119º (ESE).  The Sun will be 13º below the horizon, and there will be minimal interference from the Moon.  The maximum duration will be only 1.7 seconds, but the star will disappear completely for those inside the shadow track.

As with all predictions of this type, there is some uncertainty in the precise location of the track.  Taking into account the formal errors, the probability of observing a positive event is around 15% within the shadow track, decreasing to 7% at the 1 standard deviation limits. The latter are around 50 miles north and south of the centre line and enclose parts of the Tayside, Fife, Central, Strathclyde, Lothian, and Borders Regions (using pre-1996 boundaries for simplicity).

To see the detailed track, click on the link below to display Derek Breit's high precision plot of the event on a Google Map, and zoom in to Scotland:-

http://www.poyntsource.com/New/Google/20080411_13468.HTM

The predicted centre line is shown in green, the shadow track edges in blue, and the 1 standard deviation track in red.  (Ignore the movable grey lines.)

Although theoretically visible to the naked eye, observers may prefer to use binoculars or a telescope to see the event.

Scientifically valuable information can be obtained from accurate timings of the disappearance *and* reappearance of occulted stars. A single positive timing can yield a position relative to the star of several times higher precision than standard astrometry.  Combined timings from observers distributed across the track can yield the size and shape of the asteroid.  Of course, occultations involving bright stars give the opportunity for many more observers to take part.

Observers wishing to make serious visual timings (to better than 1 second) will need a multi-lap stopwatch or a voice recorder linked to an accurate time signal.  Those with sensitive enough video cameras, camcorders or webcams may also be able to record the events, but will need an accurate method of time-stamping the video.  This is a red star (Mr=4.0) which CCD video cameras are more sensitive to.

Serious timings of positive occultations would be welcomed by the undersigned, as would definite negative events from within the predicted shadow track.  It is normal practice to observe or record for 2 minutes either side of the predicted central occultation time above.  A specimen report form can be found at:-

http://astrosurf.com/eaon/Report%20form.htm

Please email any reports to me, or contact me if you need assistance completing the form.  Accurate latitude and longitude (WGS84 datum) can be obtained from the Google Map, before or after the event.  Elevation above mean sea level is also required.

Good luck!

Andrew Elliott

Assistant Director (Occultations), Asteroids and Remote Planets Section