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On six evenings—from Friday, May 24, through Wednesday, May 29, including all of the Memorial Day weekend—three bright planets will form a “trio,” fitting into a 5-degree field of view, low in the west-northwest sky at dusk.

Ordinary binoculars, with magnifications of 7- to 10-power, will take in all three planets—Venus, Mercury and Jupiter—simultaneously. Due to the differences in the speeds of the planets in their orbits around the sun, the arrangement of the planets will change from one night to the next.

Illustrations of the nightly arrangements of the planets appear on the Abrams Planetarium Sky Calendar, available online at www.pa.msu.edu/abrams/SkyCalendar.

Saturn will also be visible, well up in the southeastern sky on the dates of the trio, May 24-29. A telescope will easily show Saturn’s rings.

On Friday, May 24, the first evening of the trio, Venus is within 4 degrees (to the lower right) of Jupiter, while Mercury passes within 1.4 degrees to Venus’ upper right. (As a side note: The full moon tonight will be the brightest of the year.)

For the next several evenings, while the planets are in their tightest gatherings, it will be easy to notice changes in their arrangement. If you observe at the same stage of twilight each evening—for example, 30 minutes after sunset, or 45 minutes after sunset—you’ll notice the distant, slow-moving outer planet Jupiter dropping about 0.7 degrees lower each night, while the brighter inner planet Venus—on the far side of its orbit and gaining on Earth—climbs about 0.2 degree higher each night. Speedy Mercury, during the six evenings of the trio, climbs 0.6 to 0.8 degrees higher each night.

On Sunday, May 26, the evening of the most compact gathering, two planets appear within 2 degrees of Venus (the brightest planet): Jupiter to Venus’ upper left, and Mercury to Venus’ upper right. On the same evening, Mercury passes 2.4 degrees to Jupiter’s upper right.

On Monday, May 27, the compact gathering is still striking as brilliant Venus moves 1.2 degrees to the right of Jupiter, while Mercury stands 2.4 degrees above Venus, and 2.7 degrees to the upper right of Jupiter.

On Tuesday evening, May 28, the two brightest planets appear closest to each other, as Venus passes just more than 1 degree to the upper right of Jupiter. Find Mercury 2.8 degrees above Venus.

By Wednesday, May 29, the planets will have reversed their order of a week earlier. Now Mercury is the highest (within 3.3 degrees above Venus), and Jupiter is the lowest (1.7 degrees below Venus). This is the last evening all three planets fit within a 5-degree field. However, the three planets will remain in a nearly straight line for several more days as they spread farther apart.

Within the first few days of June, Jupiter will be gone, as it sets ever earlier in bright twilight before its conjunction on the far side of the sun on June 19.

Mercury will linger about 5 degrees to the upper left of Venus from June 3-10, before heading down to pass within 2 degrees lower left of Venus on June 19. Mercury will fade from view within a few days later, as it heads between the Earth and sun and becomes more backlit.

Venus will keep us company at dusk until early January 2014. In November and December 2013, Venus will attain its highest position in the evening sky this time around, with its greatest brilliancy, and will display its visually most-interesting crescent phases.

Saturn remains in the evening sky, passing through the south at dusk in June, and sinking into the west-southwest twilight glow in October. Before then, Venus will pass 3.5 degrees to the lower left of the ringed planet on Sept. 17 and 18.

Observing the trio from the Coachella Valley

Any place with a good view of sunset is fine for viewing the planet-gathering on the evenings of May 24-29. Among the best places in the Coachella Valley are those with a view of Banning Pass toward the west-northwest.

Start looking for the planets early, low in the west-northwest, where twilight is brightest, within 30 minutes after sunset. By then, brilliant Venus will be visible, closely accompanied by Jupiter. Continue until at least 45 minutes after sunset. As the sky darkens, Mercury will also be seen. Sunset in the western Coachella Valley occurs at 7:47 p.m. on May 24, and at 7:50 p.m. on May 29.

An astronomer will be on hand to assist folks in viewing the compact gathering of planets from 8:15 to 8:40 p.m. on the following evenings. Bring binoculars for the best views. After following the trio of Venus, Jupiter, and Mercury, we’ll use a telescope to view Saturn’s rings:

Saturday, May 25: In the northern part of Palm Springs, meet in Victoria Park on Via Miraleste just south of Vista Del Monte Elementary School at 8:15 p.m.

Sunday, May 26: In Idyllwild, location to be announced.

Monday, May 27: In the northern part of Cathedral City, meet on the west side of San Eljay Avenue just north of 30th Avenue at 8:15 p.m. That’s across San Eljay from the southwest entrance of James Workman Middle School. The location has a fine view toward Banning Pass.

How unusual is this gathering of planets?

The compact gathering of Venus-Jupiter-Mercury low in the west-northwest at dusk is a rare event especially worthy of observation. There will be only 14 other trios of planets (when all fit within a 5-degree field) before 2050. Of these, the next one, of Venus-Mars-Jupiter in the morning sky in October 2015, will be the most impressive, more 30 degrees up in dawn mid-twilight. With daylight saving time in effect in October, planet-gazers won’t have to get up very early to see that wonderful gathering in autumn of 2015.

For the next evening trio as good as this month’s gathering, with the planets clustering more than 4 degrees up in the middle of twilight, we’ll have to wait until September 2040.

So take advantage of this weekend’s opportunity to see three planets gather. Many years will pass before planet-watchers can enjoy as favorable a view of a similar event in the evening sky.

Robert Victor is the former as staff astronomer at Abrams Planetarium at Michigan State University.

Published in Astronomy