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Occultation of Lambda-Sagittarii
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January 2003 West Pymble, Sydney - Australia |
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A lunar occultation occurs when the Moon passes in front of a star (or planet), due to its orbit around the Earth. If you are placed in the right place, when observing an occultation, you would see the Moon firstly cover up the star, then you would see it reappear again, roughly 1 hour later. Occultations are very frequent events, however it is not so frequent to see an occultation of a relatively bright star (or planet). I was lucky enough to be able to witness this occultation of Lambda-Sagittarii, also known as Kaus Borealis, or the "tip of the teapot" in Sagittarius. Though this is not an extremely bright star, at magnitude 2.8, it is still easily visible to the naked eye. The photograph is a multiple exposure on one piece of film (photos taken every 5 minutes); not a computer composite. I only captured the second half of this event (star reappearing from the Moon's dark limb), as the first half occurred very very low on the horizon - both sky glow from the city and atmospheric effects would have prevented the film from recording the star. As the Moon rose higher in the sky due to the Earth's rotation, its motion due to its own orbit around the Earth caused it to move more slowly in the opposite direction. As it did, the star, Lambda-Sagittarii, became uncovered. You can notice how the first photo (at the bottom), no star is visible, but minute by minute, the Moon has moved further and further from the star.