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25 Dec 2019

January Astronomy: Jupiter, Mercury and Saturn Play Hide and Seek Behind the Sun This Month

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Venus climbs higher above the setting sun week by week, and late in January sets more than three hours after sunset. Mercury, after passing the far side of the sun on Jan. 10, emerges into the west-southwest evening twilight sky to the lower right of Venus by the last week of month.

Mars, very slowly brightening, appears in the southeast morning sky. Jupiter emerges into the southeast morning sky to the lower left of Mars by mid-January, followed by Saturn in early February.

By modeling the solar system on orbit charts, or—here’s a weird party idea—asking friends to act out the motions of the planets, you can see why, when an outer planet such as Mars, Jupiter or Saturn is behind the sun, it is transitioning from the evening sky to the morning sky; and why, when either inner planet, Mercury or Venus, is behind the sun, it is transitioning from morning to evening visibility. Each planet moves at a faster angular speed around the sun than any planet farther out, and the direction of rotation of the Earth on its axis is in the same sense as the revolution of the planets around the sun, i.e., counterclockwise as seen from “above,” or north of the solar system.

Search online for: “Professor Zlata! You’re just in time to be the planet Neptune!” I used to have students do this in my astronomy classes long before I ever saw the cartoon.

On evenings in January 2020, Venus climbs ever higher in a dark sky. As Venus advances 1.2 degrees per day through the zodiac compared to the sun’s 1.0 degrees, watch it pass background stars in Capricornus and Aquarius on Jan. 6-8, Jan. 21-24, and Jan. 27. Mercury emerges to the lower right of Venus in the last week of the month (30 degrees on Jan. 23, to 26 degrees on Jan. 31), and will climb highest in evening twilight around Feb. 10, when it will be 24 degrees from Venus.

In second week of January, the “Twin” stars Castor and Pollux in Gemini are at opposition to the sun and are visible all night: Low in the east-northeast at dusk, high in the south in middle of the night, and low in the west-northwest at dawn.

The moon in the morning sky: On Dec. 27, Jupiter was in conjunction on the far side of the sun, and by mid-January, it will emerge into the southeast morning sky, to the lower left of Mars and Antares. The waning moon appears in January’s morning sky, passing near Regulus on Jan. 13, Spica on Jan. 17, and Mars and Antares on Jan. 20; it appears to the upper right of Jupiter on Jan. 22.

After the new moon on Jan. 24, the moon returns to the evening sky. On Jan. 25, just a half-hour after sunset, you’ll need very clear skies to see the young, very thin crescent moon, about 1 percent full and just 3 or 4 degrees up in the west-southwest. Can you spot Mercury within 3 degrees to the moon’s lower right? Binoculars will give the best view of the delicate crescent moon with Mercury in the same field. Mercury will have just emerged from its Jan. 10 superior conjunction on the far side of the sun, and now starts its best evening appearance of the year. It will get easier to see, as Mercury gets higher and sets later each evening until the second week of February. On Jan. 27 and 28 at dusk, Venus appears 6 or 7 degrees from the lunar crescent.

After Jan. 25, the waxing moon climbs higher nightly. On Jan. 26, the 5 percent crescent appears 13 degrees to the upper left of Mercury and 16 degrees to the lower right of Venus. On Monday, Jan. 27, at dusk, the 9 percent crescent moon appears 6 degrees to the lower left of Venus. That day, find the moon about 30 degrees up in the southwest shortly before sunset, and try to spot Venus in the daytime, by looking 6 degrees to the upper right of the lunar crescent. Use a telescope for a closeup of Venus, which displays a tiny gibbous disk 15 arcseconds (1/240 of a degree) across, and 75 percent illuminated. In the coming months, Venus will be ever more fascinating to watch as it comes around to the near side of its orbit; looms ever larger in apparent size; and becomes backlighted by the sun. By late in March, as Venus stands high in the western sky, 46 degrees from the sun, it will be half illuminated, and by late in April, Venus will reach greatest brilliance, while appearing as a crescent, about one-quarter full.

The year begins with Mars as our only morning planet. On Jan. 1, we find Mars at magnitude +1.6 in the southeast, about 12 degrees to the upper right of brighter first-magnitude Antares (whose name, from Greek, ant + Ares, means rival of or opponent to Mars). The two red objects appear no more than 10 degrees apart Jan. 5-30, and no more than 5 degrees Jan. 16-20. They’re closest, within 4.8 degrees, as Mars passes north of the star on Jan. 18. Enjoy them in the same field of view of binoculars for several mornings! Watch for Jupiter emerging to the lower left of Mars in mid-January, and Saturn to the lower left of Jupiter by early February. Antares wins its ongoing brightness contest with Mars for now, but during March, Mars begins to outshine the star, and there’ll be a rare compact gathering of all three bright outer planets late that month. Earth closes in on the red planet until early October, so watch it brighten until then, to magnitude -2.6, outshining Jupiter!

How often does Mars pass Antares in our sky? If we were located at the sun, the answer would be every 687 days, or about every 22.6 months, the sidereal period of revolution of Mars around the sun. But as seen from our moving Earth, conjunctions of Mars-Antares do not occur at equal intervals. After Jan. 18, 2020, the next will occur low in the morning sky on Dec. 27, 2021, when Mars will pass 4.5 degrees north of the star. On the next two occasions, on Dec. 8, 2023, and Nov. 18, 2025, Mars and Antares will appear too close to the sun to be seen from Earth. After those, the next visible conjunction of Mars-Antares will occur very low in evening sky on Oct. 29, 2027 (3.7 degrees apart). The next two, also in the evening, will be on Oct. 7, 2029 (3.3 degrees) and Sept. 10, 2031 (2.5 degrees). Then the Mars-Antares pairings shift back to mornings, on Feb. 25, 2033 (5.3 degrees) and Jan. 27, 2035 (4.9 degrees, similar to this year’s).

Saturn will be in conjunction with the sun on Jan. 13 and will follow Jupiter into the morning sky by early February. Then all three bright outer planets will be visible in morning sky, in a gathering that will become ever more compact until Mars passes the two giant planets late in March 2020.

For a preview of sky events through August 2020, with monthly all-sky charts for dusk and dawn, and graphs of planet rising and setting times, visit the Sky Calendar extra content page at www.abramsplanetarium.org/msta.

Check the website of the Astronomical Society of the Desert at www.astrorx.org for dates and times of our evening star parties.Our primary, more-accessible location is at the Visitor Center of the Santa Rosa and San Jacinto Mountains National Monument (on Highway 74, within 4 miles south of Highway 111 in Palm Desert). Our next session there will be on Saturday, Jan. 18, from 5 to 8 p.m. Sawmill Trailhead, our high-altitude site (elevation 4,000 feet), will have a star party starting at dusk on Saturday, Jan. 25.

Remember to check the Impromptu Star Parties link on the Astronomical Society’s webpage. I’ll be offering sky watches in Palm Springs at the pedestrian bridge over Tahquitz Creek at North Riverside Drive and Camino Real, and at other locations.

On Friday, Jan. 24, I will present a preview of sky events in 2020, including the year’s rare and beautiful planetary gatherings. The event will be at the Portola Community Center, 45480 Portola Ave., in Palm Desert. Doors open at 6:30 p.m. for refreshments, and the talk begins at 7 p.m.

Abrams Planetarium publishes a monthly Sky Calendar with an evening sky map. Subscriptions are $12 per year at www.abramsplanetarium.org/skycalendar for three printed issues mailed quarterly. The March 2020 issue of the calendar will feature the rare compact gathering of the three bright outer planets in predawn skies, and Venus ascending to its greatest height in the evening sky.

Wishing you an abundance of clear skies in 2020!

Robert C. Victor was a staff astronomer at Abrams Planetarium at Michigan State University. Now retired, he often collaborates with John S. French on the Sky Calendar, and enjoys providing sky watching opportunities for a variety of groups. Robert D. Miller did graduate work in planetarium science and later astronomy and computer science at Michigan State University and remains active in research and public outreach in astronomy.

1 comment

  • Comment Link Jim G Friday, 24 January 2020 16:39 posted by Jim G

    Thanks for all your wealth of information last Tuesday night

    Report

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