Physics Photo of the Week - March 26, 2004

Warren Wilson College


Close-up of Castor and Pollux showing the contrast in colors.
In March, Gemini - "The Twins" - is high in the sky in the early evening.  On closer inspection, the twins, Castor and Pollux, are not identical.  Castor is much hotter than Pollux and as a result the color of castor is quite blue, whereas Pollux is a yellowish tint.  These colors are captured with a digital camera aimed at the constellation.  No telescope is used. 

Saturn is very prominent in Gemini this season.  The Physical Science class has measured the apparent motion of Saturn throughout December, January, and February and observed that Saturn has been moving westward throughout the season.  The December 25 location is indicated.

The fainter star Zeta Geminorum is an interesting star in that it varies in brightness with a cycle of 10.2 days.  During the past 6 weeks I have been photographing Zeta Geminorum with the digital camera without a telescope.  Here is a graph of the brightness of Zeta as a function of the fraction of a cycle.  The brightness is measured relative to the brightness of a nearby star to compensate for varying atmospheric effects.  The digital camera also permits a quantitative measure of the color of stars.  A plot of the color shows a similar pattern because the temperature of a pulsating star such as Zeta Geminorum oscillates.  I am presenting these results Saturday, Mar. 27 at the spring meeting of the NC Section of the American Association of Physics Teachers.

Donald F. Collins