A 52.2 second occultation was recorded by Dave Herald, using video OSD technique.

One clearly observed miss was recorded for this event.

View the updated prediction.

Observers:
  1    D Herald,Kambah, ACT,AU
  2(M) D Gault,Hawkesbury Heights,NSW,AU
  3(P) Prediction  18 March

    

Discussion:

The circle above is plotted at the expected 161 km diameter of Themis. With only one chord it is not possible to determine whether Dave was north or south of the central line of the event. However, assuming the updated prediction was approximately correct the much longer than expected chord of about 190 km would suggest that the chord might lie close to the central portion of the asteroid.

Unfortunately there is little other data indicating the possible shape of Themis. One other occultation on 2008 January 02 by P Maley had a chord of about 200 km.

A paper by Van Houten-Groeneveld, I., van Houten, C.J., Zappala, V.: 1979, Astron. Astrophys. Suppl. Ser. 35, 223-232. here suggests a very complex lumpy shape.

The figure below shows the Tangra light curve of the occultation.

Observational Data:

Observation details for MP (24) Themis
By Star              UCAC2 24003189
On 2010-05-15  at 19:32:53.0

_______________________________

Observer   Dave Herald
Location   Kambah, ACT,AU
Longitude  +149:03
Latitude   -35:23
Altitude   582 m
Datum      WGS84
Telescope SCT including Cass and Mak
Aperture   35 cm
Seeing     Steady Clear
Timing     GPS - time inserted Video with frame analysis
Disappearance  19:32:05.07
Reappearance   19:32:57.23
Comments:   Report prepopulated by IOTA Reporting Add-in for OW ver.1.4

_______________________________

Observer   Dave Gault
Location   Hawkesbury Heights,NSW,AU
Longitude  +150:38
Latitude   -33:39
Altitude   286 m
Datum      WGS84
Telescope Newtonian
Aperture   25 cm
Seeing     Steady Thin cloud < 2
Timing     GPS - time inserted Video with frame analysis

Missed

Comments: A cloud crossed FOV and affected all stars.
Central time of 19:32:50 UT