Physics Photo of the Week

March 28, 2008

Seasons' Sunrises
Celebrate spring with a photo of the sunrise on the spring equinox!  On the spring equinox the Sun rises due east on the celestial equator and sets due west.  The length of the night is equal to the length of the day, hence the name "equinox".

Only 3 months ago in late December the Sun appeared to be located the furthest south as it gets throughout the year.  This date near Dec. 20-22 is called the "winter solstice".  Notice how much further to the right (south in the photo below) the Sun rose on the winter solstice than it does on the equinox.  The date of the photo is not exactly on the winter solstice, but constraints of weather prevented photographing the sunrise on the exact date.  These two pictures are reproduced on the same scale.

Beginning on last fall's equinox (Sept. 22, 2007) and the spring equinox (Mar. 20, 2008) I obtained photographs of the rising Sun roughly once a week so we can see the "motion" of the sunrise point throughout the fall-winter seasons.  These photos are played in an animated sequence below.  Notice the great variety in the weather revealed in the images of the clouds at sunrise throughout the two seasons.  Each frame of the animation sequence had to be aligned because the camera was hand-held.  Astronomy image processing software was used to align each digital image.  The word "solstice" literally means the "Sun stands still".  As you notice on the animation, the Sun briefly "stops" its north-south "motion" as it reverses direction and the longer days return.
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Physics Photo of the Week is 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 

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.

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