14, 2006 Occultation of the Pleiades - Click
here for animation.
On the night of April
1, 2006 the moon passed in front of the Pleiades star cluster.
This occultation gave astronomers - professional and amateur - a good
glimpse of the moon passing in front of many of the individual members
of the Pleiades. In the photo above, Alcyone, the brightest
Pleiad, is about to be eclipsed after a fainter star. The moon
was a crescent, but the part of the moon visible in the photograph is
the dark side of the moon (still the side facing the earth). The
reason we see the dark side is due to earthshine. Earthshine is
the illumination of the side of the moon facing the earth lit up by
sunlight reflected back to the moon by the earth. This image is a
"stack" of four individual one-second exposures using a digital camera
looking through a telescope.
The moon is a bit blurred because
the moon has moved relative to the stars during that time (1
minute). The four images were aligned so that the stars are
aligned, but the moon has moved during that time. The lit portion
of the moon is on the extreme right hand side - mostly cropped off the
image. The bright part of the moon is over exposed.
The image has been enhanced to show
the colors. The Pleiades are a young star cluster and the stars
are characteristically blue-white. We cannot see the familiar
star pattern of the Pleiades due to the large image magnification
through a telescope and due to the fact that a large portion of the
star cluster is already covered up by the moon. Please see Astronomy
Picture of the Day for April 14, 2005 for the moon and the Pleiades at this
time a year ago.
Occultations of stars by the moon
are important to astronomers because the timing of the stars
disappearing behind the moon can be timed very precisely and used to
make corrections to the known orbital parameters for the moon. If
the stars are bright enough to be visible with a video camera, the
disappearance of individual stars occurs completely within a 1/30 sec
frame. Visually the disappearance of stars behind the moon is
very dramatic as the star very suddenly disappears. Amateurs can
help record the timings of occultations. Please see the
International Occultation Timing Associan (IOTA) website for details.
An animation of the Occultation is
found at the next page. The animated images are rather large, so
please have patience. Click
here for the animation.
Special thanks to Brendan Kelley for assistance in setting up the
apparatus for the photography.
Photo of the
published weekly during the academic year on Fridays by the Warren
Wilson College Physics
Department. These photos feature an interesting phenomena in
the world around us. Students, faculty, and others are invited to
submit digital (or film) photographs for publication and
explanation. Atmospheric phenomena are especially welcome.
Please send any photos to email@example.com.