2023, January 4: Earth at Perihelion, Gored Moon

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January 4, 2023: Earth is at perihelion today and closest to the sun.  The evening moon is caught between the Bull’s Horns.  Four planets shine brightly after sundown.

Photo Caption – Earth Globe (Photo by lilartsyon)

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by Jeffrey L. Hunt

Chicago, Illinois:  Sunrise, 7:18 a.m. CST; Sunset, 4:34 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.

Sunrise is at its latest time.  This continues through the 10th.  The length of daylight slowly increases during January to ten hours by the end of the month.

Jupiter’s Great Red Spot’s transit times, when it is in the center of the planet in the southern hemisphere: 7:46 UT, 17:42UT; Jan. 5, 3:38 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

Earth reaches perihelion – the closest point to the sun – at 10:17 a.m. CST today.  Planet orbits are not perfect circles, but ellipses.  Earth’s orbit is slightly out of round, about 2% from a circle.  The planet’s distance from the sun varies throughout the year, closest to the sun during early January and farthest away during early July.

Earth’s distance does not determine the seasons.  Rather this is from Earth’s tilt, so that the sun appears high in the sky during the summer season, making sunlight more direct than during the winter season when the sun is low in the sky.

For those readers near the equator, the sun is more direct around the equinoxes when it passes overhead.

Mercury is still east of the sun, setting 35 minutes after sundown.  It passes between Earth and the sun – inferior conjunction – on the 7th and quickly moves into the morning sky.

Evening Sky

Chart Caption – 2023, January 4: Venus and Saturn are in the southwest after sunset, while Jupiter is in the south.

Four bright planets continue their evening display.  Brilliant Venus continues to make its slow entrance into the southwestern sky after sunset. Look for it about 5° above the horizon at 45 minutes after sundown. The planet continues to emerge from bright evening twilight, setting this evening 83 minutes after the sun.

Venus shows phases through a telescope, similar to the moon’s phases.  The moon’s phase names refer to the fraction of the moon’s surface in illumination and relationship to the sun.  While Venus shows crescent and gibbous phases, as well has half-full illuminations, using the moon phase names do not match the location of Venus in the sky.  Instead of waxing and waning, it is better to refer to them as evening crescents or morning gibbous phases.  Since the moon is in the evening sky, that term is best use for the current Venusian phases.  While the planet is very low in the sky, it is showing an evening gibbous that is 95% illuminated.

Venus is quickly stepping eastward and toward Saturn and Jupiter.  The Jovian Giants are plodding eastward, while Venus covers about two full moon diameters in the sky from night to night.  The gap to Saturn this evening is 20.4°. Saturn is to the upper left of Venus and over 20° above the horizon.  Look each clear evening to see Venus close in on the Ringed Wonder.  Venus passes Saturn on the 22nd.  They look close together in the sky, but Saturn is nearly seven times farther away than Venus.

After the conjunction with Saturn, Venus maintains its eastward pace and begins to overtake Jupiter, passing the Jovian Giant on March 1st.  From February 20 through March 11, Venus is within 10° of Jupiter, making a magnificent display of two bright planets in the western sky after sundown.

Chart Caption – 2023, January 4: The gibbous moon seems caught between the Bull’s horns. Mars is 8.4° from Aldebaran.

Farther eastward, the bright gibbous moon, 96% illuminated, seems to be caught between the Bull’s horns, Elnath and Zeta Tauri, not a good place to be.  The lunar orb is 14.6° to the lower left of bright Mars.

The Red Planet is slowly retrograding in front of Taurus, although the bright moonlight whitewashes the stars from easy view.  The planet is 8.4° to the upper left of Aldebaran.

Mars begins to move eastward again on the 12th and passes Aldebaran for the third conjunction of a triple conjunction series on the 30th.

At 9:38 p.m. CST, when Jupiter is 15° up in the west-southwest, the Great Red Spot is visible through telescopes in the center of the planet in the southern hemisphere.  When the planet is at this altitude – height above the horizon – the atmosphere tends to make the view blurry and shaky.  Telescopic sky watchers farther westward see the planet higher in the sky and in clearer, settled air.

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