2023, May 10: Venus at Castor’s Foot, Evening’s Starry Disappearance


May 10: Brilliant Evening Star Venus and Mars shine against Gemini’s sidereal backdrop. Sirius, Betelgeuse, and Aldebaran are making their final evening appearances of the year.

Photo Caption – 2022, April 5: Mars passes Saturn. Venus is nearby.


by Jeffrey L. Hunt

Chicago, Illinois:  Sunrise, 5:36 a.m. CDT; Sunset, 7:59 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 10: The moon is east of the Teapot before sunrise.

An hour before sunrise, the gibbous moon, 74% illuminated, is over 20° above the southern horizon and to the east of the Teapot of Sagittarius.  The morning half phase (Last Quarter) occurs on the 12th at 3:28 p.m. CDT.

The lunar orb is headed toward Saturn for a conjunction in three mornings.

Chart Caption – 2023, May 10: Saturn is higher in the southeast each morning before daybreak.

This morning the Ringed Wonder is about the same altitude – height above the horizon – as the moon, but in the southeast.  The planet is higher in the sky each morning.  Now rising nearly two hours, fifty minutes before the sun, the planet is nearly reaching a place for telescopic viewing.

Jupiter follows Saturn across the eastern horizon about two hours after the Ringed Wonder. The Jovian Giant is over 3° above the east-northeast horizon at 30 minutes before sunrise.  A binocular is needed to find the planet.

Mercury is speeding toward a difficult-to-see appearance in the morning sky next month.  Still immersed in bright sunlight, the planet rises twenty-five minutes before the sun.

Evening Sky

Chart Caption – Venus moves in front of Gemini, May 7-June 2, 2023.

Brilliant Venus continues as the showpiece in the western sky after sunset. The Evening Star can be simply described as “that bright star” in the west.  It steps eastward in front of Gemini, near Castor’s foot, 3.6° to the upper right of Propus (η Gem on the chart), the toe, and 4.0° to the upper right of Tejat Posterior, the heel.

Chart Caption – 2023, May 10: Venus is near the star cluster Messier 35 (M 35) during the evening through a binocular.

Through a binocular, the planet is 2.4° to the upper right of the star cluster cataloged as Messier 35 (M 35 on the chart).  Galactic clusters, also known as open clusters, populate the spiral arms of galaxies.  They can be used as indicators of stellar distances and ages.

Photo Caption – The Pleiades star cluster. (U.S. Naval Observatory)

The most famous open cluster is the Seven Sisters bunch. This cluster has blue stars, indicating they are relatively young compared to yellow stars like the sun.  The cluster is currently disappearing into evening twilight, to the lower right of Venus.

The bright blue stars convert the hydrogen gas at their cores at prodigious rates.  Stars exist when the outward flow of heat energy is balanced by the inward pull of their gravity.  They have more gases than the sun and are considerably brighter.

When the core hydrogen fuel is converted to helium and other heavier elements, the temperatures must increase to fuse the heavier atomic nuclei.  Those higher core temperatures inflate the stars to larger sizes and the outer layers turn reddish orange.

Photo Caption – The Beehive or Praesepe star cluster (National Science Foundation Photo).

Stars like the sun convert their hydrogen to helium at slower rates and can exist as relatively stable stars for billions of years. Clusters with blue stars are younger than the sun, although they may have red giants in them.

Messier 35 can be seen without a binocular’s optical assist in locales far from the perpetual glow of outdoor lighting.  It is interesting to note that the cluster’s location is 2.3° to the northwest of the sun’s location on the summer solstice.

Through a telescope, Venus shows a gibbous phase that is 62% illuminated, an evening gibbous Venus.  The phase continues to decrease toward the evening half phase.  While Venus phases resemble lunar phases, the names used for the moon are not appropriate for Venus because they do not occur in a similar cycle.

Chart Caption – 2023, May 10: Sirius, Betelgeuse, and Aldebaran are making their last evening appearances in the western sky after sundown.

At forty-five minutes after sundown, look for Sirius, nighttime’s brightest star, over 6° above the west-southwest horizon. This may be one of the last nights to see the star, known as the heliacal setting.  This occurs as the star disappears into the blush of evening twilight.  It reappears in the morning sky before sunrise about the time of the Perseid meteor shower each year.

Aldebaran, Taurus’ brightest star, leaves the evening sky a few evenings after Sirius, followed by Betelgeuse about a week later.

Chart Caption – 2023, May 10: Venus and Mars appear against Gemini’s sidereal backdrop.

Mars, marching eastward near Gemini’s Pollux, is over 20° to the upper left of Venus.  Fading in brightness the Red Planet is dimmer than Pollux, but brighter than Castor.

The two planets are easily located at 45 minutes after nightfall, but look later, near the end of twilight when Gemini’s dimmer stars are visible.  The pattern resembles two side-by-side stick figures.

Venus continues to overtake Mars.  Watch the changing locations of the planets each evening.



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