Author Topic: [BAA-ebulletin 00985] Rare occultation of a 5th magnitude star by an asteroid  (Read 386 times)

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[BAA-ebulletin 00985] Rare occultation of a 5th magnitude star by an asteroid visible from UK on Sept 9/10
(c) 2017 British Astronomical Association

On the night of Saturday, September 9 at 23:44 UT (00:44 BST on September 10) the asteroid (6925) Susumu (mag 17.8V) is predicted to occult star sigma(1) Tauri (HIP 21673, mag 5.1V). A detailed account by Alex Pratt of this very favourable event is available at:

Given that the star is bright enough to be visible to the unaided eye, and that it is a spectroscopic binary star, many observers may be treated to a 'double' shadow cast by the star system transecting the mid-UK region. The maximum duration of an occultation from any one location is about 2 seconds when the star disappears from view. Be watchful however for secondary events, either arising from the binary nature of the star or the distinct possibility that the asteroid is a binary system too. Although the marked uncertainty in the exact location of the track is about 100 km, given duplicity in the star/asteroid, observers several hundred km either side of the centre-line should watch for a positive occultation event. Likewise, start observing a few minutes ahead of the due time and continue a few minutes after too in order to capture unexpected phenomena. Note that the star is in Taurus and will be fairly low towards your eastern horizon.

Do please make every effort, weather permitting, to observe this especially rare event. If you are able to use a video camera hooked up to some form of optical aid then do consider using it, as this type of permanent record is invaluable observation-wise. Visual observers should also attempt to time the event, both the duration of the disappearance and the absolute time if at all possible. An easy way to add time marks to your video record (say after the start and before the end)is to momentarily shine a flashlight or similar near the entrance of your optics, synchronising the flash as accurately as possible to some reliable time signal.

Good luck everyone!

Richard Miles
Director, Asteroids and Remote Planets Section
2017 September 07 09:24 UT