Physics Photo of the Week

December 17, 2010

Solstice Approaching...
The winter solstice is the date around Dec. 21 or 22 every year year when the Sun is the furthest south relative to the celestial equator.  As a result the northern hemisphere receives the least light due to the low altitude of the Sun as well as the least amount of daylight. 

The above photo shows the Sun rising on the solstice on D
animated gif, be sure to use a browser that supports animated gifsecember 21, 2009.  Note it's position rising over the crest of the Swannanoa Mountains across the Valley from WWC campus.  The animated photo at right shows the positions of the rising Sun throughout November, 2009 to Feb 2010 last winter.  A graphical calendar was also added so you can observe that the Sun is furthest to the right (south) on the solstice.  On the date of the solstice, the position of the Sun appears to stand still, hence the word "solstice" for "stationary Sun".

A much more subtle effect near the December solstice is the time of latest sunrise.  In spite of the fact that there are the fewest hours of daylight on the solstice, the latest sunrise doesn't occur until about 2 weeks later in our latitudes.  Notice that the image with the latest sunrise doesn't occur until January 4.  Likewise the earliest sunset occurs early in December - about 2 weeks before the solstice (see the PPOW for December 11, 2009).  The offset of the latest sunrise and earliest sunset is due to the elliptical orbit of the Earth (also explained in the December 11, 2009 PPOW).  This effect is much more pronounced in the December solstice than the June solstice because the Earth is significantly closer to the Sun in the northern hemisphere winter.

Total Lunar Eclipse.  On December 21, 2010 (next Tuesday) - between 1:00 am and dawn - there is also a total eclipse of the Moon visible from all of North America.  Hope for clear skies for this coincidence between the solstice and the lunar eclipse!  Most important: You must get up way before dawn on December 21 to see the eclipse!  Totality begins 2:41 AM Eastern Standard Time and totality ends at 5:53 AM EST.

This is the last Physics Photo of the Week for 2010 due to the Christmas Holidays.  The next Physics Photo is not scheduled to be posted until January 21, 2011.  Have a Merry Christmas and a Happy New Year!

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 

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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