2023, February 21: Morning Sky Map, Evening Moon, Planet Showcase

February 21, 2023: Use the sky map to find winter morning’s stars.  The moon joins Venus as it approaches Jupiter. Mars marches eastward in a planetary showcase.

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by Jeffrey L. Hunt

Chicago, Illinois:  Sunrise, 6:38 a.m. CST; Sunset, 5:31 p.m. CST.  Check local sources for sunrise and sunset times for your location.  Times are calculated from the U.S. Naval Observatory’s MICA computer program.

Jupiter’s Great Red Spot’s transit times, when it is in the center of the planet in the southern hemisphere: 7:49 UT, 17:45 UT; Feb. 22, 3:41 UT. Convert the time to your time zone. In the US, subtract five hours for EST, six hours for CST, and so on.  Use a telescope to see the spot.  Times are from Sky & Telescope magazine.

Here is today’s planet forecast:

Morning Sky

The morning sky is without a bright planet or the moon.  Mercury rises only 36 minutes before sunup amid the bright light of approaching dawn.  Saturn rises a few minutes before the sun.  It is lost in bright sunlight for about the next month, appearing in the eastern sky before sunrise around the time of the equinox.

This morning’s chart is a circular map showing the entire sky an hour before sunrise.  These charts can be confusing because of their orientation and their circular shapes.

First think about a terrestrial map.  Where are you when you look at a map of Earth?  You’re in the sky looking down on Earth, with north to the top of the map and east to the right.

When considering a celestial map, the sky watcher is on Earth looking up.  So, the circular map is the sky above your head with the overhead point marked with a “+” sign.  The directions are labelled usually with the letters for the cardinal points.  On the accompanying map, generated from the US Naval Observatory’s MICA computer program, the directions are identified with their azimuth:  North is 0°; East, 90°; South, 180°; and West, 270°.

In the theoretical use, hold the map above your head and rotate the circle to match your directions.  Quickly, you’ll see that this is uncomfortable and you’ll go after that digital sky map.  However, there’s an easier way.

Hold the map in a comfortable position and rotate it in the direction you’re looking.  For example, start with Antares.  It is near the horizon circle, low in the south, on the map.  That’s where it is in the sky during late winter an hour before sunrise.

Now look east.  Rotate the map so that east is at the bottom.  Notice that Vega is more than halfway between the east horizon and the “+” sign marking overhead.  It’ll be halfway up in the eastern sky.  Deneb is less than halfway between the east-northeast horizon and overhead, while Altair is about one-third of the way between the east-southeast horizon and overhead.  The two stars are in these places in the sky.

Notice that the morning sky has other bright stars, including Spica, Regulus, and Arcturus.

The example to check your celestial map reading ability is to locate the Big Dipper on the chart.  What direction and how high in the sky will you look to find it?

Evening Sky

This evening, the crescent moon, 4% illuminated, joins Venus and Jupiter in the western sky.

Begin by looking in the west-southwest at forty-five minutes after sundown.  Brilliant Venus is nearly 20° above the horizon, with Jupiter 8.2° to the upper left. 

The moon is 6.4° to the lower left of Venus.  Notice earthshine on the night portion, sunlight reflected from Earth’s features illuminates the lunar darkness.

The night’s three brightest celestial objects are within a circle that is 15° in diameter.  This does not occur frequently.  Tomorrow the bunching is within an 8° circle.

Venus is quickly overtaking Jupiter, cutting the gap about 1°, about two-full moon diameters, each evening.  Venus slips past Jupiter on March 1^st, staying within 10° through March 11^th.

Farther eastward Mars marches eastward in front of Taurus. An hour after sunset when the dimmer stars are visible, Mars is high in the south, 10.2° to the upper left of Aldebaran and 7.1° to the lower right of Elnath, the Bull’s southern horn.

During the next week watch the Red Planet pass between Elnath and Epsilon Tauri (ε Tau on the chart).  The second star is part of the letter “V” shaped group that outlines the Bull’s head.  Epsilon is at the top of the V, opposite Aldebaran.  A binocular may be needed to identify it.  It is dimmer than the stars in the Pleiades star cluster, to its upper right.

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