Mizar and Alcor are a famous pair of stars located in the constellation of Ursa Major, the Great Bear. Known for thousands of years, the pair were thought to be a good test of eyesight in ancient times. Mizar is the middle star of the bear’s tail and much brighter than faint Alcor. However, keen-sighted observers will be able to see Alcor with just their eyes. It appears in the ten o’clock position, in relation to Mizar, when Ursa Major is highest in the sky.
The pair make for a fine sight through binoculars with Mizar appearing about twice as bright as Alcor. However, when the pair are observed at low power through a telescope (35x is all that’s required) Mizar itself is seen to be double. Both stars appear blue-white and about the same brightness. (There’s also another faint star that forms a triangle with the Mizar pair and Alcor. In reality, neither this star or Alcor is anywhere near Mizar in space and the alignment is purely by chance.)
(Click on an image to enlarge.)
03:44 UT – Last Quarter Moon. (Naked eye, Sagittarius, pre-dawn sky.)
23:32 UT – The just-past last quarter Moon passes dwarf planet Ceres. (Ceres: magnitude 8.4. Capricornus, pre-dawn sky.)
Jupiter’s diameter shrinks to 40”. (Magnitude -2.3. Cancer, evening sky.)
The constellation Virgo (the Virgin) culminates at midnight tonight. (Naked eye, all night.)
The bright multiple stars Mizar and Alcor culminates at midnight tonight. (Mizar: magnitude 2.3. Alcor: magnitude 4.0. Naked eye, Ursa Major, all night. See images above.)
Events in bold involve objects and/or events that are easily visible with the naked eye.
All times are in Universal Time (UTC). To convert the time to your timezone, click here.
Learn more about upcoming astronomical events in 2015 An Astronomical Year (Kindle Edition) and The Astronomical Almanac (2015-2019) (Kindle Edition and Paperback Edition) and 2016 An Astronomical Year (North American Kindle Edition.)
The Amateur Astronomer’s Notebook allows astronomers to log 150 observing sessions and includes an appendix of hundreds of suggested deep sky objects.
If you have any comments or questions, please feel free to contact me at astronomywriter “at” gmail.com