Although occultations can occur in a variety of ways, the heavenly body most often involved is our moon which inevitably will occult (or eclipse) background stars, other planets as well as asteroids. The study of occultations is important, for example, for the study of the moon's limb and its profile thanks to the grazing of lunar features such as mountains.

Without doubt, the most stunning example of the moon occulting another body is that involving the sun which, of course, leads to a solar eclipse. This special example of an occultation is available elsewhere on this site.

What is perhaps more interesting and certainly most challenging is the observation and/or imaging of the occultation of a star by an asteroid, for these events occur along very narrow footprints and last from fractions to a handful of seconds. These events are particularly informative scientifically since the absence or presence of an occultation from a particular location is equally meaningful and helps provide an indirect assessment of the asteroid's size and, more importantly, shape as well as the possible existence of associated satellites.

Note: The asteroidal occultation below was particularly challenging due to the fact that it occurred with the sun a mere three degrees below the horizon and rising. To this end, a combination of filters effectively yielding a longpass H-α transmission line were used to mitigate the effects of the bright sky while simultaneously permitting a viable opportunity to record this event which was predicted to last a mere 1.1 seconds at the center of the overhead pass (the imaging was performed six kilometers from the predicted occultation path center but well within the predicted footprint). Further details in relation to this occultation are available on the IOTA website here whereas occultation maps for Europe and Greece are available here and here, respectively.

The occultation for this particular location was predicted to be at 07:24:42 UT+3. As a precautionary measure with respect to a possible error in the predicted time, however small or large, the imaging was initiated at 07:23:00 UT+3 and allowed to run until 07:26:00 UT+3 so that errors slightly in excess of a minute on either side of the predicted time would not have impacted the successful imaging of the event.

Note: The maximum occultation duration was predicted to be 1.1 seconds. However, the video clip below represents an occultation duration of 2.05 seconds and in spite of the fact that the observing location was 6 km north of the predicted occultation center. The animation below is based on five key frames: (1) Regulus immediately prior to ingress; (2) ingress stage by Rhodope; (3) complete occultation; (4) egress by Rhodope; and (5) Regulus immediately after egress.