Gemini seen high-- its "head" stars aligned

Event Date: March 7th

Time: 8:21(.13) PM

Brief

Castor and Pollux, the Gemini (twin) head stars, are about 4 1/2º in separation.  As seen from our latitude, they are not far from zenith during 20 minutes sandwiching the exact transit time, before and after.  For the second image below, I have set a time for when the two are not only high in the sky shortly before transit; they are the exact azimuth.  Why does this matter?  It really doesn't, since they are easy enough to slew from one to the other with no optical aid with the a telescope.  This is just one of those nights that I have little else to write about, and decided to get silly with crazy star patterns and alignments to the horizon!

  Here are the two stars with the the entire constellation seen high in the sky, followed by a zoom-in of the two with the alt-az grid.  Looking at the altitude lines, notice that the spacing of the stars between the lines is almost exactly the same.  If using binoculars, hold them steady and level to the ground, noticing that the two stars are in line up-and-down with each other.

click on images to enlarge: courtesy of Starry Night Pro Plus, version 6.4.3, by Simulation Curriculum Corp.

Detailed

   When we see the stars rise in the east-northeast, they are similar in azimuth already.  When we see them setting more than 15 hours later, they are much different in azimuth and more similar in altitude.  Most mid-northern latitude viewers see it this latter way, as the northern stars circle around the celestial pole each day.  At declinations 28º and 32º for Pollux and Castor respectfully, they are further north than the Sun at the June solstice when it comes near them.  Castor is seen a little closer to zenith at southern US latitudes, and transits (near) there.

   As a multiple star system, Castor has two components, which coulde be seen with the unaided eye if they didn't orbit so close to the star!  A powerful enough telescope can split them however, as they are only 4.4 arc-seconds from Castor.

   Pollux is not quite as interesting.  Unlike hot, younger Castor, Pollux is an old, dying star, already a yellow-orange color as a giant.  It is 10 solar radii large, which isn't too big compared to some stars (especially Antares, Betelgeuse and some other red giants), yet it is likely still growing bigger.

Find out more about both stars at this link: