Physics Photo of the Week
Astronomy Picture of the Day has featured Comet Holmes 11 times
since the October 24 eruption. This is the second PPOW feature on
Comet Holmes is Growing
Image acquired by Jenna Blakley
and Jake Lyerly
Image taken by Chloe Stuber, Pengye Su, and Emily Woodall.
Processed by Jenna Blakley
Image acquired by Taylor Sanford,
Gordon Jones, and Valerie Moore
Astronomers as well as the astronomy students at Warren Wilson have
been ` recording Comet Holmes during the past
month. This comet is
highly unusual in that it suddenly erupted in late October releasing a
large cloud of gas and dust. This cloud of gas and dust has been
steadily expanding. It is expanding into the vacuum of
space. The radiation pressure from the sun is also forcing the
gas to move further away from the sun to form a tail. The
location of the sun relative to the Earth for the comet at this time
forces the tail in the direction directly behind the comet,
consequently we cannot see the general shape of the tail. We are
looking at the comet head on. The comet is also travelling
further away from the sun. However, the cloud is growing in size
faster than the comet is receding - thus appearing larger and larger.
The cloud of gas and dust has originated from one major eruption.
Since this eruption the gas has been expanding into the vacuum of
space, becomming more diffuse. As a result of the gas becoming
less dense, it has become less bright - fewer molecules to backscatter
the sunlight. The comet is so bright in the first image that only
a couple of stars are visible.
In the last image the comet is quite faint compared to the stars.
Consequently we can see many more stars through the cloud of the
comet. In each image, the brightness levels is adjusted so that
the comet does not look overexposed. The image contrast is
maximized in the last image to make the comet look "normal", but the
large increase in contrast results in many more stars made visible.
Most of the light from the comet is reflected or scattered sunlight -
scattered by the gas and dust of the coma. Visual observers using
binoculars report a greenish appearance. Careful spectral
analysis by C.
Buil reveal faint emission features caused by fluorescence.
Below are two images of the comet taken with a digital camera (Canon
A630) with out a telescope. A number of 15 sec exposures were
taken and co-added. We can
see how much the comet has moved in the 18 day interim. The
bright star in the center of the photographs is Mirfak - the brightest
star in the constellation of Perseus.
Photo by Don Collins from Warren Wilson College
Photo by Emily Woodall and Don
Collins from Bee Tree Gap on Blue Ridge Parkway
These two images are reproduced at the same scale. The reason the
picture on the left shows sharper star images is that the picture on
the left was taken with a 4x optical zoom. The image on the right
was taken with normal focal length, but the picture had to be expanded
digitally to match the scale at left. The digital zoom loses
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 firstname.lastname@example.org.
here to see the Physics Photo
the Week Archive.
Observers are invited to submit
digital photos to: