MBCAA Observatory

Occultation by 27 Euterpe

Observed: 2 Nov 2015

Michel Bonnardeau
3 Nov 2015
corrected 10 Apr 2017 (shadow size)


The minor planet 27 Euterpe was observed occulting a 12.1 mag star: the duration of the event was 23.6±1.7s.


The occultation of the 12.1 mag star 2UCAC 39644999 by the 10.1 mag asteroid 21 Euterpe on Nov 2, 2015 was predicted on Steve Preston's Predictions Website. The details of the prediction are here.


The observation was carried out with a Meade LX200 203mm f/6.3 Schmidt-Cassegrain telescope, a Clear fiter and a SBIG ST7E camera (KAF401E CCD). A few seconds before the occultation, the camera obturator is opened, the telescope equatorial motor still running,
3 seconds after the begin of the exposure, the motor is shut down,
and 60 seconds after the begin of the exposure the obturator is closed.

The resulting image show the stars (the 3 seconds the motor was running) with trails (the 57 seconds the motor was not running). The occultation shows up as a decrease of the star trail intensity. Actually this drop in the trail is rather weak as the asteroid was quite bright.

The time was recorded by the computer, the clock of which was reset over an internet time server, owing to Dimension4 and net time. Futhermore, the computer clock was checked by listening over a wire telephone to the Horloge Parlante (Observatoire de Paris, France).


A scan of the star trail is:

The time goes from right to left.

The end of the trace is at:
xE = 6 ± 1 pixels
tE = 04:44:63 UT ± 0.5 s

The trace begin is at:
xB = 585.5 ± 0.5 pixels
and the trace duration is:
D = 57 s

The ingress and the egress are at:
ingress = 430 ± 5 pixels
egress = 190 ± 5 pixels
that is, in time:
tin = tE-(ingress-xF)*D/(xB-xE) = 04:44:21.3 UT ± 1.2 s
teg = tE-(egress-xE)*D/(xB-xE) = 04:44:44.9 UT ± 1.2 s

The duration of the event was then:
teg-tin = 23.6 ± 1.7 s
and the time at the mid-event was:
(teg+tin)/2 = 04:44:33.1 UT ± 1.7 s

The report send to PLANOCCULT is here (may not be on-line).

Technical notes

Telescope and camera configuration.

Computer and software configuration.

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