The grazing occultation took place in the early morning hours of a Saturday and required a one-hour trip across the Rimutaka mountain range to Martinborough in the Wairarapa, north of Wellington. The fact that Sigma Scorpii is a multiple (quadruple) star and the prospect of an exciting event made all the effort seem worthwhile. It turned out to be a very windy night with dense clouds drifting across the sky. Therefore the choice of taking the little 6-cm refractor (The "Cologne" Refractor) mounted on a heavy (in comparison) HEQ-5 mount along on the expedition was an appropriate one.

I ended up with 13.5 minutes of video (at 25 frames per second), whose evaluation took the better part of 12 hours. In the process I edited it down to a 4.5-minute highlights version. While some events are clearly visible, it was not immediately clear if some dimming and blinking was just a result of the moving clouds.

I was able to identify and evaluate three distinct events. The first one was the 3-step disappearance of sigma Sco behind the dark edge of the Moon. The second event showed a complete crossing of a Lunar valley in about 30 seconds, where both the reappearance and disappearance of the star happened in steps (figures 1 and 2). The last event was extremely difficult to measure as the star skimmed along the edge of the Moon, egressing from behind a brightly lit mountain. As cloud set in, it became obvious that the star had well separated from the Lunar surface. I have roughly sketched my results on the assumed Lunar profile (figure 3)

Figure 1: Sequence of video stills showing the stages of the "Valley Crossing" event.

Figure 2: Light-curve of the "Valley Crossing" event produced in LiMovie.

Figure 3: Rough sketch (red) of the observation data against the assumed Lunar profile.

Seeing the star cross a Lunar valley and disappear on the other side in stages, as it is a multiple (quadruple) star system, was quite a sight (refer to video). I can only recommend such an experience. More on occultaions at the Occultation Section of the Royal Astronomical Society of New Zealand (RASNZ).

Video of the "Valley Crossing":
[1.5MB WMV] - [11.87MB AVI]

Technical details:
Observation Time: 20090731-13:05 to 20090731-13:19 UT
Telescope: 6 cm Refractor, f = 71 cm
Mount: HEQ-5 driven
Instrumentation: monochrome CCD Video camera (KT&C 350BH) with Kiwi-OSD recording directly to laptop PC