Archive for May 23, 2022

05/23/2022 – Ephemeris – the Moon and the morning planets plus the Big Dipper’s stars Mizar and Alcor

May 23, 2022 Comments off

This is Bob Moler with Ephemeris for Monday, May 23rd. Today the Sun will be up for 15 hours and 6 minutes, setting at 9:13, and it will rise tomorrow at 6:05. The Moon, 1 day past last quarter, will rise at 3:44 tomorrow morning.

This week, the Moon is in the process of passing the morning planets. This morning it passed Saturn. Tomorrow afternoon and evening it will pass Mars, then Jupiter. By Thursday morning, the Moon will be below and left of Jupiter. Thursday evening, it will pass Venus.

Back to tonight’s sky, the Big Dipper is nearly overhead. In its handle is a star or two that are interesting. It’s the star at the bend in the handle. It’s called Mizar. Next to it, for those with good eyesight, is a dimmer star, called Alcor. The name Mizar is from the Arabic, meaning apron or cover, while Alcor means the forgotten one. Before optometrists, the ability to actually see both stars was a test for good eyesight, especially for Arabic warriors. The pair is also known as the “Horse and the Rider”.

The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EDT, UT – 4 hours). They may be different for your location.


The Moon passing the morning planets 5/23/22 to 5/27/22

The Moon passing the morning planets at 5 am 5/23/2022 to 5/27/2022. Click on the image to enlarge it. Created using Stellarium and GIMP.

Mizar and Alcor in the Big Dipper

Mizar and Alcor in the Big Dipper as it is nearly overhead towards the north. Click on the image to enlarge it. Created using Stellarium.

Alcor seems to be a true companion to Mizar, since they are at the same distance of 81.7 light years. Alcor also has an unseen companion star. Mizar also has a much closer companion star that can be seen in a telescope. On top of that, each of them has another unseen companion star. Six stars for the price of two. What a deal.

How can you detect a companion star that can’t be seen? When analyzing a star’s spectra, the companion star betrays it presence by its chemical absorption lines shifting with respect to its primary due to the Doppler effect of its motion.