Physics Photo of the Week
December
18, 2009
2 Solstices
This is a panoramic shot of the horizon near Warren Wilson College
looking due east. Usually a multishot panorama consists of
several photos pointing at different angles taken immediately after
each other. However, in this pan shot, the two images were taken
almost exactly 6 months apart! The image on the right was taken
very close to the winter solstice on Dec. 24, 2007. The image on
the left was taken the following June 20, 2008.
Not only do we see the Sun rising in drastically different locations,
but the sky color varies greatly. Both days were obviously very
clear, but the summer air usually contains much more water vapor and
aerosols that add the red color to the sky. Actually the water
aerosols (microscopic suspended water droplets) scatters the blue
wavelengths out of the line of sight with the Sun, so the
sumer sunrise sky lacks the blue wavelengths. The lack of
moisture in the winter air scatters much less of the sunlight.
Thus the winter sunrise is white and the sky is blue.
The location of the sunrise depends on the season of the Earth in its
orbit around the Sun. Since the axis of the Earth is tilted 23.5
degrees from the orbital plane, the perspective of the Sun changes from
due east on the equinox to 23.5 degrees north or south of due
East. The shift in the horizontal position of the sunrise between
the winter and summer solstices is a bit larger than twice the 23.5
degrees. In the picture below the two paths slanted upwards and
to the right represent the apparent path the Sun follows in its
rising. That direction depends on our latitude (35.5 degrees at
Warren Wilson College). The solar path is tilted 35.5 degrees off
the vertical. 47 degrees is separation of the two rising paths,
but on a direction perpendicular to the two paths. The angular
separation along the horizontal is 47 degrees divided by the cosine of
the latitude angle. This results in 58 degrees. See the
diagram below.
Enjoy the winter solstice this coming Monday, December 21.
Have a
Merry Christmas, Happy Hannakah, a Joyous New Year and may these
holidays be safe for you and your families. This is the last
Physics Photo of the Week for 2009
due to winter break at the college. We'll see you back on January
22,
2010.
Physics
Photo of the
Week is
published weekly during the academic year on Fridays by the Warren
Wilson College Physics
Department. These photos feature 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 dcollins@warren-wilson.edu.
All photos and discussions are copyright by Donald
Collins or by the person credited for the photo and/or
discussion. These photos and discussions may be used for private
individual use or educational use. Any commercial use without
written permission of the photoprovider is forbidden.
Click
here
to see the Physics Photo
of
the Week Archive.
Observers are invited to submit
digital photos to:
