January 18, 2021: Without a bright morning planet, bright Arcturus and the constellation Bootes the Herdsman is high in the south. The crescent moon is in the early evening sky. Mars is near the planet Uranus. They are high in the south-southeast as night falls.
by Jeffrey L. Hunt
Chicago, Illinois: Sunrise, 7:14 a.m. CST; Sunset, 4:49 p.m. CST. Check local sources for sunrise and sunset times for your location.
With no bright planets easily visible in the morning sky, a few of the sky’s brightest stars are visible before sunrise.
Yesterday, we peered at Spica and Virgo that are low in the sky in the west-southwest.
This morning look to the upper left of Spica, high in the south. There you’ll find topaz Arcturus. The star’s name means “the bear-guard.”
This star is part of the constellation Bootes the Herdsman or the Bear Driver. The pattern resembles a kite, and as visualized in the accompanying chart, three stars could be the tail.
Arcturus and the constellation follow the Great Bear (Big Dipper) around the sky. On the chart, the star Alkaid is the end of the dipper’s handle (bear’s tail).
Arcturus’ temperature is less than the sun, but it is at least 20 times larger than our central star. It is considered a “red giant,” farther along in its stellar life-cycle than the sun. Similar stars are larger, intrinsically brighter, cooler than sun-like stars. While they are not distinctly red in color, they are redder than our sun. A binocular shows the yellow-orange of the star.
Arcturus is the brightest star in the northern half of the sky. (While we see Sirius from the northern hemisphere, it is in the southern half of the celestial sphere.) Arcturus’ competition for stellar brightness champion in the celestial northern hemisphere: Vega, Capella, Procyon, and Betelgeuse.
Corona Borealis (Northern Crown) is the neighbor of Bootes. The brightest star Gemma or Alphecca (“the broken or fractured one”) is the constellation’s brightest star. Some historical reference to the stars sideways “C” shape could indicate a crown or a broken circle of stars, which Alphecca’s name indicates.
Gemma is distinctly dimmer than Arcturus, but the constellation’s pattern is easy to identify.
Evening Sky
Mercury is low in the west-southwest after sunset. It is only 6° above the horizon. Houses, trees, and other terrain could block your view. Use a binocular to find this planet that resembles a star. Even through a telescope there’s not much to see because of the planet’s low altitude and the bright sky.
In the evening sky, the crescent moon – over 30% illuminated – is low in the east-southwest after sunset. It sets around 11 p.m. local time.
In a few evenings, Mars passes Uranus, which is at the limit of human eyesight. Before the moon becomes too bright, attempt to locate the distant world. On January 20, the brighter moon is closer to Mars, making the Red Planet easier to identify, but the moon’s brightness will make it more challenging to find the planet Uranus.
This evening, look high in the south-southeast for Mars. It’s the bright “star” over two-thirds of the way from the horizon to overhead. Mars is in front of the starry background of Aries. The constellation’s brightest stars are far from the ecliptic, the invisible track where the planets appear to move. Hamal, the brightest, is 9.0° above Mars this evening.
With a binocular find the star 19 Arietis (19 Ari on the chart). The star is 0.9° to the upper left of Mars. Uranus is twice that distance to the lower left of the Red Planet.
Its color is slightly aquamarine. You’ll need a telescope with a magnification of at least 100x to see the spherical shape of the planet.
Uranus revolves around the sun every 84 earth years. Mars passes it again August 2, 2022.
Read about Mars during January.
Detailed Note: One hour before sunrise, find Capella (α Aur, m = 0.1) about 7° in altitude above the west-northwest horizon. Thirty minutes after sunset, Mercury (m = −0.8) is over 6° up in the west-southwest. Farther east, the crescent moon (5.8d, 32%) – nearly halfway up in the south-southwest – is in Cetus. Mars is over 62° in altitude in the south-southeast, 9.0° below Hamal, 0.9° to the lower right of 19 Ari, and 1.8° to the upper right of Uranus.
Read more about the planets during January.
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