January 2, 2023: Bright winter stars are in the western sky before sunrise. After sundown, four planets, Venus, Saturn, Jupiter, and Mars, along with the moon are visible.
by Jeffrey L. Hunt
Chicago, Illinois: Sunrise, 7:18 a.m. CST; Sunset, 4:31 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: 6:07 UT, 16:03 UT; Jan 3, 1:59 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
The morning sky is without a bright planet. Some of the stars that shine during winter’s evenings are setting in the western sky an hour before sunup. They are Procyon, Pollux, Castor, and Capella.
Procyon is the brightest star in Canis Minor, the Little Dog. The name means “before the dog.” Find it about 10° up in the west. From Chicago’s latitude it rises approximately twenty minutes before Sirius, the Dog Star. It is the sixth brightest star visible from the mid-northern latitudes and the fourth brightest north of the celestial equator, the imaginary circle in the sky above Earth’s equator.
Castor and Pollux, the Gemini Twins, are less than one-third of the way up in the west-northwest. Pollux is nearly a full magnitude brighter than Castor.
In the stellar magnitude system. A lower number indicates that a star is brighter. Brightest celestial objects have negative magnitudes. Sirius, the night’s brightest star, is listed at −1.5. Jupiter is −2.8. A star of sixth magnitude is at the limit of human eyesight.
Each step on the magnitude scale indicates a brightness difference of 2.5 times, well 2.512. Five magnitude steps indicate 100 times brightness difference. (For those who want to perform the mathematics, it’s 2.512 to the fifth power equals 100.) With a one magnitude brightness difference, Pollux is about 2.5 times brighter than Castor.
The fourth star, Capella – meaning “the little she goat,” is about 15° up in the northwest. It is the fourth brightest star visible from Chicago’s latitude and the third brightest north of the celestial equator.
Arcturus, the brightest star in the northern half of the sky, is high in the south-southeast at this hour, while Vega, the second brightest, is one-third of the way up in the east-northeast.
The top four stars in the northern half of the sky are visible at this hour – Arcturus, Vega, Capella, and Procyon. We see them again in this orientation during late spring evenings.
Evening Sky
Four bright planets are in the evening sky. Starting in the southwest at forty-five minutes after sundown, Venus is about 5° above the horizon. Find an observing spot with a clear horizon in that direction.
Saturn, plodding slowly eastward in front of the stars of Capricornus, is about 20° above the southwest horizon and over 20° to the upper left of Venus.
The Evening Star is quickly stepping eastward and overtakes the Ringed Wonder on the 22nd. Watch Venus close the gap each clear evening.
Bright Jupiter is over halfway up in the south and nearly 40° to the upper left of Saturn. These giant planets are not close together again until 2040.
Venus catches Jupiter in a close conjunction on March 1st. They make a spectacular pair in the western sky from February 20th until March 11th.
Farther eastward, the bright gibbous moon, 86% illuminated, is about halfway up in the east, 10.3° to the upper right of Mars.
The Pleiades star cluster is 3.5° to the upper left of the lunar orb and in the same binocular field with it. If you use a binocular to see the cluster, move the moon out of the field of view. The moon may leave a temporary afterimage in your vision, like that from a camera flash. To minimize that effect, move the binocular slightly to remove the moon from the view.
Mars is 8.4° to the upper left of Aldebaran, the brightest star in Taurus. The planet ends its retrograde in 10 nights and begins to move eastward again. It passes Aldebaran for the third conjunction in a triple conjunction series at month’s end.
The stars of Orion are rising in the eastern sky at sundown, in particular Betelgeuse and Rigel. The latter star rises at sunset in three evenings. The pattern is in the east-southeast about 90 minutes after sundown.
After the Big Dipper, Orion is likely the second star pattern that children from the northern hemisphere learn. Three stars that form the Hunter’s belt are easy to recognize. Pointing downward toward the horizon at 90 minutes after sundown, they indicate the direction to Sirius. Orion’s shoulders are marked by Betelgeuse and Bellatrix. Rigel and Saiph dot the knees. Notice the contrast in star color from Betelgeuse to Rigel.
The celestial equator splits Orion so that Betelgeuse is north of the circle, while Rigel is south. This makes Betelgeuse the fifth brightest star in the northern half of the sky, although Rigel appears about one-third of a magnitude brighter than Betelgeuse.
Of all night’s stars visible from the mid-northern latitudes, Rigel is fifth and Betelgeuse is seventh.
Both stars are very bright, Betelgeuse is 25,000 times brighter than the sun, but Rigel is nearly 100,000 times brighter than our central star.
Betelgeuse is larger than Rigel, even though it does not have the same intrinsic brightness. Here’s how that works. Imagine two globes of similar size that are heated to different temperatures, one the temperature of Betelgeuse, the second to Rigel’s temperature. The blue-white globe representing Rigel is very bright compared to Betelgeuse. To make the globe representing Betelgeuse as bright as Rigel, the globe must be increased in size. Bright red stars are larger than bright blue-white stars.
If we could bring both stars to our solar system and put them in the sun’s place, Rigel would cover the inner solar system nearly to Mercury’s orbit. The larger Betelgeuse would cover the inner solar system beyond Mars’ orbit and nearly halfway to Jupiter! The orbital paths of Mercury, Venus, Earth, and Mars would be inside the star.
Each clear evening, continue to note Saturn’s place in the starfield of eastern Capricornus through a binocular. The planet is east of Nashira, 1.4° to the upper left of the star, and moving toward Deneb Algedi. Other dimmer stars that are cataloged with numbers are in the field as well.
For sky watchers with telescopes, Jupiter’s Great Red Spot is center stage in the planet’s southern hemisphere at 7:59 p.m. CST. The Jovian Giant is over 30° up in the southwest in Chicago. Observers farther west see the planet higher in the sky.
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