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27 Feb 2020

March Astronomy: The Three Bright Outer Planets Converge This Month for a Once-in-20-Years Rendezvous

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In the western sky after sunset, Venus in late March attains its highest position at dusk and its longest duration of visibility in a dark sky for 2020.

All three bright outer planets—Mars, Jupiter and Saturn—cluster in the southeast before dawn. Don’t miss their rare, once-in-20-years compact gathering from March 18-31. In mid-March, Mercury reaches its highest position during a poor morning twilight appearance, very low in the east-southeast. Binoculars will help you find the innermost planet well to lower left of the outer-planet threesome.

In the March evening sky, the huge Winter Hexagon of bright stars is in fine view, with Sirius, the brightest star, crossing through the south, and Capella, its second-brightest member, passing north of overhead. In clockwise order, locate Sirius, Procyon, Pollux-Castor, Capella, Aldebaran, Rigel and back to Sirius. Orion’s shoulder—red supergiant and future supernova Betelgeuse, inside the hexagon—is still uncharacteristically faint at this writing (matching the other shoulder star), but is expected to recover some of its brilliance before the Winter Hexagon departs from our view in the west in mid-May. Venus far outshines all these stars, and climbs to its highest point around the date of greatest elongation (maximum angular distance from the sun), on March 24. Telescopes show Venus’ phase, then half full. The crescent moon skips past Venus on March 27 and 28, passing widely south of the planet. Catch the Pleiades star cluster (the Seven Sisters) within 5 degrees of Venus for 11 evenings, March 29-April 8. Binoculars give stunning nightly views!

On April 1, two days before the very close pairing of Venus with third-magnitude Alcyone, or Eta Tauri, the brightest member of the Pleiades, they’re within 1.8 degrees. They’ll be less than 0.3 degrees apart on April 3, when binoculars will certainly be handy for observing the very close conjunction! Venus will be moving east against background stars by about 0.9 degrees per day, pulling away from the Pleiades. On April 5, Venus and Alcyone are 1.9 degrees apart.

In the morning sky, bright Jupiter attracts our attention to the southeast, where the three bright outer planets span 18.5 degrees on March 1, closing to 6.3 degrees at month’s end. Can you spot Mercury in the twilight glow to their lower left? Binoculars help.

Early risers will be well rewarded by the rare morning scenes depicted on the illustration from the March 2020 Sky Calendar below. Be sure to catch the compact gathering of the moon and three planets within a span of 8.3 degrees on March 18, and the same three planets spanning just 7.1 to 6.3 degrees during March 20-31, as Mars, in the foreground, passes from Jupiter toward Saturn. Watch Mars pass within 0.7 degrees of Jupiter on March 20, and 0.9 degrees of Saturn on March 31. Several morning scenes of the threesome, as well as scenes of the moon’s return to evening sky, appear in this excerpt from the March Sky Calendar.

Check the website of the Astronomical Society of the Desert at www.astrorx.org for a schedule of star parties. The primary, more-accessible location for our star parties is the Visitor Center of the Santa Rosa and San Jacinto Mountains National Monument, on Highway 111, within four miles south of Highway 111 in Palm Desert. Our next session there will be on Saturday, March 28, from 7 to 10 p.m. Sawmill Trailhead, our high-altitude site (elevation 4,000 feet), will have a star party starting at dusk on Saturday, March 21. The list of star parties on the society’s website includes maps and directions for both locations. Star parties can be cancelled in poor observing weather.

Also, 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. Some sessions will be held in the daytime or at dusk to observe the changing phases of Venus, and some in the predawn to follow the gathering of the three bright outer planets.

Abrams Planetarium publishes a monthly Sky Calendar with an evening sky map. Subscriptions are $12 per year 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.

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, mostly in the California desert and in Michigan.

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