2023, October 21: Three Bright Planets, First Quarter Moon

Astronomy, Sky Watching
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October 21, 2023: Venus, Jupiter, and Saturn are easy to locate during nighttime hours.  The First Quarter moon phase occurs this evening.

2014, October 1: Jupiter, Regulus before sunrise.
Chart Caption – 2014, October 1: Jupiter, Regulus before sunrise.

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by Jeffrey L. Hunt

Chicago, Illinois:  Sunrise, 7:10 a.m. CDT; Sunset, 6:00 p.m. CDT.  Check local sources for sunrise and sunset times. Times are calculated by the US Naval Observatory’s MICA computer program.

Summaries of Current Sky Events
Summary for Venus as a Morning Star, 2023-24

See this week’s highlights article.

Here is today’s planet forecast:

Morning Sky

Chart Caption – 2023, October 21: During morning twilight, Venus is in the east-southeast before sunrise, in front of Leo.

Two planets, Venus and Jupiter, are easy to locate during morning twilight.  Brilliant Venus is nearly 30° above the east-southeast horizon at one hour before sunrise. As twilight brightens toward daybreak, the planet is still visible.

Venus is in front of Leo’s distant stars.  The Morning Star steps eastward each morning compared to the stellar background.  Use a binocular to see the dimmer star Rho Leonis (ρ Leo on the chart), 4.7° to the planet’s upper right.

Venus is approaching its greatest separation from the sun, as viewed from our planet, known as the greatest elongation.  Because the planet’s orbit is inside Earth’s, Venus does not stray far from the sun.  After inferior conjunction, between Earth and the central star, Venus speeds away and ahead of our planet.  It brightens and then reaches a point when it rises early and appears high in the sky.  Then it begins to rise later after it sort of rounds the curvature of its solar orbit.  Like a dog on a chain attached to a yard spike, the planet reaches the end of its slack and it heads toward the farthest part of its orbit.  The greatest elongation occurs in two mornings and coincidentally passes Chertan, Leo’s “two small ribs,” in a wide conjunction. 

This morning Venus rises five minutes short of four hours and nearly an hour after Saturn sets.

Chart Caption – 2023, October 21: Bright Jupiter is in the west before daybreak, nearly between Hamal and Menkar.

Not as bright as Venus, Jupiter is in the western sky during morning twilight.  The Jovian Giant is retrograding in front of Aries, 12.1° to the left of Hamal, the constellation’s brightest star.

In a week, Jupiter passes between Hamal and Menkar, part of Cetus.

Photo Caption – Jupiter (NASA Photo)

For sky watchers in the western hemisphere with telescopes, Jupiter’s Great Red Spot is visible at the center of the planet in the southern hemisphere twice today.  The first is at 3:39 a.m. CDT and the second, 11:30 p.m. CDT, two Jupiter days after the first appearance.

Evening Sky

Photo Caption – Mercury as Never Seen Before. (NASA photo)

After superior conjunction yesterday, Mercury is moving toward an appearance in the western sky after sundown.  This evening the planet sets only five minutes after the sun sets.  Mars follows eighteen minutes later.

Chart Caption – 2023, October 21: The nearly-half full moon is in the south after sundown.

An hour after sundown, the nearly half-full moon is in the southern sky.  The half-full (First Quarter) phase occurs at 10:29 p.m. CDT.

Chart Caption – 2023, October 21: Saturn is in the southeastern sky near Deneb Algedi during early evening hours.

Saturn is farther eastward, nearly 35° to the moon’s upper left and almost 30° above the southeast horizon.  The Ringed Wonder is retrograding in front of Aquarius, 6.8° to the left of Deneb Algedi.  Both fit into the same binocular field of view.

At this hour, Jupiter is low in the east-northeast.  Wait another hour to see it about 15° up in the east.  As the midnight hour approaches the planet is about halfway up in the southeast and in the west again tomorrow before sunrise.

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