Physics Photo of the Week

  Physics Photo of the Week March 27, 2026 Equinox Sunrise - Photo and Discussion by Donald Collins This year's equinox photo was taken the day before last week's equinox of March 20, 2026.  On the equinox, the Sun rises in the direct east as opposed to the winter solstice when the Sun rises in the southeast - way off the right side of the photo. The equinox literally means "equal nights (and days).  The length of nighttime and daytime are equal.  "Nighttime" is defined as the time between sunset and sunrise, and "daytime" is the time between sunrise and sunset.  At the equinox, the daytime length equals the nighttime length. An interesting effect in the picture above is the long dark streak radiating away from the Sun's position - made more visible by the zoomed-in image below: The dark streak is a long shadow cast by a cloud about 1/3 the way between the Sun's position and the upper left corner of the zoomed-in image.  The reddish color of ...

Physics Photo of the Week March 20, 2026   Ice Sprouts - Photos by Henry Willis; Discussion by Donald Collins My friend, Henry Willis, sent me this photo of "ice sprouts" taken during a trek in the Great Smokies National Park earlier this winter.  Although fairly common, ice sprouts this large are quite unusual.  These sprouts are about 2 inches tall.  Ice sprouts are formed when bare ground, that has been saturated with rain water, freezes.  The amazing property of water is that the ice phase is less dense than water.  Ice cubes float on top of your drink of iced tea.  Most solid objects are more dense than their liquid counterparts.  When the muddy soil freezes, the freezing takes place on the top of the mud. The frozen surface confines the remaining water beneath the surface.  The remaining water under the top shell freezes and expands; pressure builds up and the expansion force breaks through cracks in the shell; the water is forced out a...