2023, May 21: Morning Arcturus, Evening Celestial Display


May 21, 2023: Find Arcturus in the west before sunrise.  After sunset, Venus, Mars, and the crescent moon are on exhibition.

Photo Caption – 2022, July 30: The crescent moon with earthshine. (Photo by MJB)


by Jeffrey L. Hunt

Chicago, Illinois:  Sunrise, 5:25 a.m. CDT; Sunset, 8:10 p.m. CDT.  Check local sources for sunrise and sunset times for your location.  Times are calculated by the U.S. Naval Observatory’s MICA computer program.

Summaries of Current Sky Events

Here is today’s planet forecast:

Morning Sky

Chart Caption – 2023, May 21: Arcturus is in the west during morning hours.

Step outside about 90 minutes before daybreak, when the sky is still fairly dark.  Topaz Arcturus is the bright star that is about one-third of the way up in the western sky. It is the brightest star in the northern half of the sky; that is, north of the celestial equator, the imaginary circle in the sky above Earth’s equator. The star is 37 light years away and shines with an intensity of 100 suns.

The star’s name means “bear guard” and along with its constellation, Boötes, they chase the Great Bear (Big Dipper).  At this hour the dipper is at the same altitude – height above the horizon – as Boötes in the northwest.

In Chicago, Arcturus has connections to great events in the city. The 1933 World’s Fair used Arcturus’ light to energize photoelectric cells attached at the eyepieces of four telescopes in the eastern U.S. – Yerkes Observatory, University of Illinois, Allegheny Observatory, and Harvard Observatory – to switch on a searchlight that signaled the beginning of the fair.

Arcturus was thought to be 40 light years away.  The 1933 fair was 40 years after the 1893 Columbian Exposition that also occurred in Chicago.

There is a competing story about how the searchlight was signaled from the light of a telescope set up on the fairgrounds.

The constellation Corona Borealis – the Northern Crown – is to the left of Boötes.  Alphecca – meaning “the broken or fractured one” – is the pattern’s brightest star, although it is 10 times fainter than bright Arcturus.

Chart Caption – 2023, May 21: Jupiter and Saturn are in the eastern sky before daybreak.

Farther eastward, Jupiter and Saturn shine from the eastern sky before daybreak.  At forty-five minutes before sunup, the Jovian Giant is over 5° above the east horizon.  It is easy to locate from a spot that has a clear view of the horizon.  A hilltop or elevated structure helps with the view.

Saturn, considerably dimmer than Jupiter, is nearly 25° above the southeast horizon.  While dimmer than Venus and Jupiter, the Ringed Wonder is among the brightest stars in the sky this morning.

The star Fomalhaut is above the southeast horizon, slightly higher than Jupiter and nearly 20° to the lower right of the Ringed Wonder.

Mercury continues to scamper into the morning sky, rising less than 30 minutes after Jupiter. It is still dim and lost in sunlight when the speedy planet is high enough to be seen.

Evening Sky

Chart Caption – 2023, May 21: Venus, Mars, and the crescent moon are in the western sky after nightfall.

Look for the crescent moon after sundown.  At forty-five minutes after sunset, Venus is over 15° up in the west-northwest, 5.8° to the upper left of Elnath, Taurus’ northern horn, and 17.0° to the lower right of brilliant Venus.

Photo Caption – 2021, January 15: The thin waxing moon with earthshine, reflected sunlight from Earth’s features gently illuminates the lunar night.

Look carefully at the non-sunlit portion of the moon.  It gently glows with earthshine, sunlight reflected from Earth’s oceans, clouds, and land.  The effect can be seen without optical assistance. A binocular or spotting scope is helpful to see it. Capture earthshine in a photo with a tripod-mounted camera and an exposure of up to a few seconds.

The Evening Star is stepping eastward in front of Gemini, 8.8° below Castor and Pollux.  Notice that the planet makes nearly an isosceles triangle with the two stars.

From Chicago and other locations in the eastern regions of time zones, Venus sets before midnight and later from areas in the western regions of their time boundaries.

Through a telescope, the planet displays an evening crescent phase, 57% illuminated. the phase continues to shrink, reaching the evening half phase next month.

Venus continues to close the gap to Mars.  This evening the separation is 15.3°.

The Red Planet is less than halfway up in the west and 8.9° to the upper left of Pollux.  It is marching eastward in front of Cancer’s dim stars.

Mars is not as bright as might be expected.  Its brightness in our sky depends on its distance from our planet.  This evening it is nearly three times farther away than when it was closest six months ago.  Consequently, the planet is dimmer in the sky.

Watch the moon skip past Venus and Mars during the next several evenings.



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