2023, September 15: Brilliant Venus, Look for Mercury

Photo Caption – 2015, September 21: Venus, Jupiter, Mars, Regulus


by Jeffrey L. Hunt

Chicago, Illinois:  Sunrise, 6:31 a.m. CDT; Sunset, 7:00 p.m. CDT.  Check local sources for sunrise and sunset times. Times are calculated by the US Naval Observatory’s MICA computer program.

After today, sunset occurs in Chicago before 7:00 p.m. CDT until March 17, 2024. Daylight lasts twelve hours, twenty-minutes.  The equinox occurs September 23rd at 1:50 a.m. CDT.  Because of the definition of sunrise and sunset, and the bending of sunlight when the central star is near the horizon, daylight and night are nearly equal on the 25th and 26th.  By month’s end, daylight lasts eleven hours, forty-eight minutes at Chicago’s latitude.

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

Here is today’s planet forecast:

Morning Sky

Chart Caption – 2023, September 15: Venus, Sirius, Procyon, and Regulus are in the eastern sky before sunrise.

Begin looking for Mercury this morning.  A binocular is needed to find it to the lower left of Regulus.  First, find the brighter planets.

Venus rises nearly three hours before sunrise.  It continues to gain rising time, nearly an hour before it reaches the maximum rising time interval before sunrise during late October.

Venus is in its interval of greatest brightness.  This continues through the 21st.  On the 19th, Venus is at its greatest illuminated extent, an interesting term.  The planet is at a geometric location where its phase covers the largest area of the sky for this appearance.  It corresponds to when the planet is at its brightest.  This morning the planet is a morning crescent phase that is 24% illuminated.  Look for the phase through a spotting scope or telescope.  The cusps or horns of the crescent point away from the sun.  It resembles a waning crescent moon, but waxing and waning are not used for Venusian phases.

One hour before sunrise, brilliant Venus is in the eastern sky, over 20° above the horizon.  It continues to rise three minutes earlier each morning, even though it is stepping quickly eastward.  The Morning Star is approaching Regulus, Leo’s brightest star, that is nearly 10° up in the sky. This morning the separation is 16.6°.    The conjunction occurs October 9.

Look for Sirius in the southeast, nearly the same altitude – height above the horizon – as Venus.  During the remainder of the month, the brightest planet and the brightest star are nearly the same altitude during morning twilight.  There is no impending conjunction because Sirius is about 40° from the ecliptic, unlike Regulus that is the brightest star closest to the solar system’s plane.

Procyon, meaning “before the dog,” is above an imaginary line from Venus to Sirius.  From the mid-northern latitudes, it rises about 30 minutes before Sirius, the Dog Star.  When Procyon is near the eastern horizon, Sirius rises soon thereafter.

Chart Caption – 2023, September 15: Jupiter is high in the southwest, near Hamal, Menkar, and the Pleiades star cluster.

Farther westward, bright Jupiter is high in the southwest, 13.5° to the lower left of Hamal, Aries’ brightest star, and 11.2° to the upper right of Menkar, Cetus’ nostril.  It is about 16° to the lower right of the Pleiades star cluster, part of Taurus.

Chart Caption – Jupiter’s retrograde motion against the starfield is demonstrated for 2023.

Jupiter is retrograding in front of Aries.  As Earth laps the more distant planets, those worlds seem to back up or move westward compared to the starry background.  As the Jovian Giant moves westward, watch it appear to move between Hamal and Menkar during the next several days.

Chart Caption – 2023, September 15: Venus, Regulus, and Mercury at 30 minutes before daybreak.

Mercury rises seventy minutes before the sun. 

Chart Caption – 2023, September 15: Mercury and Regulus are visible using overlapping binocular fields of view.

Forty minutes later, that is thirty minutes before daybreak, the planet is nearly 7° up in the east and 8.0° to the lower left of Regulus.  The planet and the star are about the same brightness.  A binocular is needed to see them, but they do not fit into the same field of view. Find one of them and then move the binocular either up or down to see the second celestial body.

Diagram Caption – A movie maker’s view of what a binocular sees Free public domain CC0 image.

Remember that unlike what is portrayed in a movie, a binocular looks at one circle not a field of overlapping circles. The binocular chart of Regulus and Mercury shows overlapping binocular fields not the movie scene view demonstrated above.

Tomorrow morning, the two are slightly closer than this morning and overlapping binocular fields are needed to see them, although Mercury is a little brighter than Regulus.  The speedy planet continues to brighten each morning.  In a week it can be easily spotted without the optical assist.

Evening Sky

Chart Caption – 2023, September 15: Saturn is in the southeast during the evening.

Mars continues its slow slide into bright twilight.  It is dimmer than might be expected.  Tomorrow evening, as a last hurrah for this appearance, the very thin crescent moon and the Red Planet appear in the same binocular field low in the western sky after sunset.

Saturn rises before sunset, and two hours after nightfall, the Ringed Wonder is over 25° above the southeast horizon.  The planet is brighter than most stars this evening, but it is not remarkably bright like brilliant Venus and Jupiter.

The planet is retrograding in front of Aquarius, 9.3° to the upper right of Skat, the Aquarian’s leg, and 9.6° to the right of Lambda Aquarii (λ Aqr on the chart).  The two stars do not fit into the same binocular field with Saturn. From urban and suburban settings, outdoor lighting likely washes them out, and they are not visible without the binocular’s optical assist.

Dimmer than Saturn, the star Fomalhaut, meaning “the mouth of the southern fish,” is about 20° below the planet and less than 10° above the horizon.

During the night as Earth spins and the wheel of the sky seems to turn westward, Saturn is in the south before midnight and low in the west-southwest during morning twilight.  As Venus rises over three hours before sunrise tomorrow morning, Saturn is about 10° up in the west-southwest.

The Venus-Saturn opposition occurs October 10th, when the two planets are 180° apart in the sky.  Because Saturn disappears into the thicker layers of air near the horizon that blur and dim the celestial bodies, the last date when Venus and Saturn are visible simultaneously occurs sooner.  Track them.  What is the last date you see them in the sky at the same time?

Jupiter rises over two hours after sundown.  It appears to follow Saturn westward, appearing in the south over two hours before sunrise and in the southwest during morning twilight.


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