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30 Jan 2020

February Astronomy: The Three Bright Outer Planets Are Coming Together—and What Happened to Betelgeuse?

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In the western evening sky, Mercury reaches one of its highest positions at dusk for 2020. In the predawn darkness of Feb. 18, the moon covers and uncovers Mars. Meanwhile, all three bright outer planets—bright Jupiter, with Mars to its upper right, and Saturn to its lower left—are gradually coming together in the southeast before dawn, until their rare, once-in-20-years compact gathering in late March!

You won’t fail to notice brilliant Venus well up in the west-southwest to west at dusk. Mercury makes an appearance to its lower right. Mercury shines at magnitude -1 on Feb. 1, fading to magnitude 0 on Feb. 13, and magnitude +1 by Feb. 17; it then dims rapidly and drops into bright twilight within a few days. Mercury lingers 24 degrees from Venus Feb. 4-11. The revolution of the planets around the sun is counterclockwise, as viewed from above the northern side of the solar system. Fast-moving Mercury and Venus are gaining on Earth and coming around from the far side to near side of the sun. This causes Mercury (but not cloud-covered Venus) to fade as the planet displays narrowing crescent phases on the near side of its orbit. Mercury appears at greatest elongation, 18 degrees from the sun, on Feb. 10.

Sirius, the “Dog Star” and brightest of the nighttime stars, twinkles vigorously in the southeast. It is the lowest member of the huge Winter Hexagon of stars of first magnitude or brighter. In clockwise order, they are Sirius, Procyon, Pollux (with fainter twin Castor just 4.5 degrees away), Capella (nearly overhead), Aldebaran, Rigel and back to Sirius. Betelgeuse is normally the brightest star inside the boundaries of the Hexagon, but something has happened to this star! At the time of this writing, Betelgeuse appears barely as bright as Bellatrix, the other shoulder of Orion. Keep an eye on Betelgeuse, comparing it to other stars of known brightness; refer to the resources posted at the end of this article.

Other bright stars in February at dusk include Deneb, the last star of the Summer Triangle to slip away in the northwest, and Regulus, heart of Leo, at opposition to the sun on Feb. 18.

Jupiter is the brightest morning “star,” with Mars to its upper right, and Saturn emerging early in February to Jupiter’s lower left. Ranking next after Jupiter in brightness are golden Arcturus, high in the southwest, and blue-white Vega, high in the east-northeast to east. Look for Spica in the southwest, far below Arcturus; Regulus, sinking in the west to west-northwest; reddish Antares, heart of the Scorpion, in the south; and the stars Altair and Deneb completing the Summer Triangle in the eastern sky. By observing the sky at dawn in February, we can get a “sneak preview” of the stars in the positions we’ll see them in at dusk in July.

For three consecutive mornings, Feb. 18-20, the waning crescent moon appears close to each of the three bright outer planets.In fact, on Feb. 18, before dawn, the moon actually occults (covers) Mars. It’s the bright leading edge of the moon that covers Mars, so an optical aid will be needed. From the Coachella Valley, Mars will disappear behind the leading bright edge of the moon at 3:36 a.m., and reappear at the moon’s unlit side at 4:30 a.m. Note the disappearance occurs very low in the sky, only 5 degrees up as seen from our valley. By the time of reappearance, the moon and Mars will be 14 degrees up the southeast. The next morning, on Feb. 19, the moon will be close to Jupiter, and on Feb. 20, close to Saturn.

As you observe these events before sunrise, imagine you are on the forward side of Spaceship Earth in our orbit around the sun. The sun is below the horizon to your left, while our spaceship is gaining on the three bright outer planets ahead of us. We’ll overtake Jupiter and Saturn within a week of each other in July, as we pass between those giant planets and the sun. They’ll appear at opposition, 180 degrees from the sun, and so when the moon appears near them in July, it will appear full. Not until October will we overtake fast-moving Mars, and see a full moon near the red planet.

There are wide pairings of the crescent moon and Venus on Feb. 26 and 27. You can also look just before sunset for Venus in daylight, 10 degrees to the upper right of the moon on Feb. 26, and 6-7 degrees to the lower right of the moon on Feb. 27.

On Friday, Feb. 7, author and columnist Dennis Mammana will present an astronomy lecture, “From Darkness Comes Light,” at the Portola Community Center, at 45480 Portola Ave., in Palm Desert. Doors open at 6:30 p.m. for refreshments, and the talk begins at 7 p.m.

Check the website of the Astronomical Society of the Desert at www.astrorx.org for more information on the lecture and 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 74, within 4 miles south of Highway 111, in Palm Desert. Our next session there will be on Saturday, Feb. 29, from 6 to 9 p.m.Sawmill Trailhead, our high-altitude site (elevation 4,000 feet), will have a star party starting at dusk on Saturday, Feb. 22.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 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 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 clear skies!

For more on Betelgeuse:

http://stars.astro.illinois.edu/sow/betelgeuse.html

https://www.nytimes.com/interactive/2020/01/09/science/betelgeuse-supernova-fading.html

https://www.skyandtelescope.com/observing/fainting-betelgeuse/

https://www.aavso.org/sites/default/files/10startutorial-2013.pdf

https://www.aavso.org/aavso-alert-notice-690

https://www.aavso.org/

(Enter “alf ori” into the “Pick a Star” box, then select “Plot a light curve” or “Check recent observations.”)

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. Robert D. Miller did graduate work in planetarium science and later astronomy and computer science at Michigan State University. He remains active in research and public outreach in astronomy.Dr. Jeffrey L. Hunt, a retired planetarium director now living in the Chicago area, has taught astronomy and sky watching to all ages. He studied astronomy education at Abrams Planetarium at Michigan State University. Jeff provided the graphs of planet rising and setting times (below); writes an astronomy blog at jeffreylhunt.wordpress.com; and can be followed on Twitter at @jeff_hunt.

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