Physics Photo of the Week
March 25, 2011
Equinox Sun Rise
On the Equinox the Sun rises in the
due east and follows the celestial equator throughout the day.
This photo, taken on March 21, 2011 (the day after the spring equinox
when we had clear weather) shows the Sun at sunrise (7:47 am Eastern
Daylight Time) plus a time series of filtered Sun images taken at 20
second intervals and added together to simulate a time exposure that
lasted until about 9:23 am EDT. The much shorter sunstreak on at
the right was taken on Feb. 11, 2011 and was stopped at the same time
of day (9:23 if we had DST year round). If we had a time exposure
of the Sun on the winter solstice, the streak would be even further to
the right and considerably shorter still. This sequence shows the
dramatic change in day length as a result of the seasons.
The equinox Sun path in the sky follows the celestial equator: the part
of the sky that lies directly above the Earth's equator. At our
latitude of 35 degrees, the celestial equator is tilted 35 degrees from
the vertical. The winter Sun's path lies south of and parallel to
the celestial equator. If we were viewing the sunrises from the
Earth's equator, the paths would be vertical.
To image the Sun, a special filter was placed over the camera lens
to prevent over-exposure. The filter is called a "Neutral Density
5" that is the light is attennuated by a factor of 105.
These images are part of a long-term project that will last at
least a year (4 seasons). Stay tuned...
Photo of the
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 firstname.lastname@example.org.
All photos and discussions are copyright by Donald
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