September/October 2017 – Vol. 30 No. 1

Evening Planets in School Year 2016-17

Posted: Monday, September 19th, 2016

by Robert C. Victor. Thanks to Robert D. Miller for the monthly twilight charts,

and to Dr. Jeffrey L. Hunt for the graphs of planets’ rising and setting times. 

Monthly sky maps for September 2016 through June 2017 depict the changing positions of the five bright planets and the 16 stars of first magnitude or brighter visible from southern California. Planets are plotted daily at mid-twilight, when the Sun is 9° below the horizon, 39 to 53 minutes after sunset, depending on latitude and time of year. Star positions are shown as continuous curves, as stars drift west with the advancing season, a result of the Earth’s revolution about the Sun. Inspect the charts in sequence to follow a planet’s progress through the weeks or months of its apparition. Keep in mind that the Sun is below the western horizon. Mercury and Venus, inner planets, climb up from the western horizon only a limited distance, and then fall back to the same horizon. The outer planets Mars, Jupiter, and Saturn begin evening visibility at the eastern horizon (opposite the Sun) and end their apparitions sinking into the western twilight glow. 

Links to monthly evening twilight charts: 

For southern California –

2016:    SEP    OCT   NOV    DEC

2017:    JAN    FEB  MAR    APR   MAY    JUN 

For northern California – 

2016:    SEP    OCT   NOV    DEC

2017:    JAN    FEB  MAR    APR   MAY    JUN

Links to graphs of planets’ evening setting times:

Venus will dramatically improve in visibility in late 2016, as the fast-moving inner planet gains on Earth and moves farther away from its superior conjunction beyond the Sun on June 6. By late August or early September 2016, Venus sets about one hour after sunset. Note from the graphs of the planets’ setting times that Venus sets after the Sun until late in March 2017. By late October or early November 2016, Venus sets two hours after sunset, and will be noticed in a fully darkened sky before it sets. In early December 2016, Venus will set a full three hours after sunset. On January 12, 2017, Venus will reach greatest elongation, 47° east (upper left) of the setting Sun, and will set nearly four hours after sundown. Around then, Venus will be of increasing interest for viewing through a telescope, as the planet will display a tiny “half-moon” shape, even at low magnification. February and March will be even better! As Venus swings closer to Earth, it will grow rapidly in apparent size and display ever thinner crescent phases while the planet becomes more backlighted by the Sun. Greatest brilliance at mag. –4.8 occurs in mid-February 2017. Even slight optical aid such as binoculars will then reveal a crescent about one-quarter full, easy to observe in daylight or in bright twilight. Inferior conjunction (Venus nearly between Earth and Sun) will occur on March 25. On this occasion, Venus passes over 8° north of the Sun, so it will be possible to observe the very thin crescent Venus both after sunset and before sunrise for a few days (and even in the daytime if proper precautions are taken) as the planet shifts into the eastern morning sky.

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Jupiter disappears into the bright evening twilight glow by early September 2016. After passing conjunction beyond the Sun on Sept. 25, Jupiter reappears low in the eastern morning twilight glow about 15 days later. During Oct. 10-12, emerging Jupiter climbs past departing Mercury, at the end of the inner planet’s brief but favorable morning apparition. With each passing month, Jupiter rises earlier in the night, until on April 7, 2017 it will be at opposition, rising around sunset and visible all night. After opposition, in spring and summer of 2017, Jupiter will be a prominent object in the evening sky in the constellation Virgo, not far from the star Spica. Through a telescope, Jupiter’s two dark equatorial cloud belts and its four satellites discovered by Galileo are prime attractions.

Saturn is still visible in the evening sky in September 2016, lingering only 6° from the reddish first-magnitude star Antares, heart of the Scorpion. If you want students to have good telescopic views of the rings, be sure to schedule a viewing session early in this school year, while Saturn is still fairly high. By mid-November, Saturn will set before twilight ends, and around Thanksgiving, it departs. Saturn passes conjunction with the Sun on December 10, and by New Year’s Day 2017, it emerges low in the southeastern morning twilight. The ringed planet then rises nearly two hours earlier per month. Saturn fans will have to wait until mid-June 2017 for Saturn to reach opposition, when it will rise around sunset and again become available for early evening observation.

Keep in mind that evening sky watching sessions in June must start at a late hour, so if you want to provide younger students a chance to view Saturn’s rings without staying up late, plan a session for later in summer, or in early autumn.

Best dates to observe planets are not the same from one year to the next. Venus returns to the same position with respect to Earth and Sun, such as inferior conjunction, at intervals of just under 1.6 years or 19.2 months, resulting in five full cycles of evening and morning visibility in just under 8 years. Oppositions of Jupiter occur just over a month later each year – it takes Earth an extra month to catch up to it again after a year. Saturn’s oppositions occur about 12 or 13 days later annually. Jupiter and Saturn will come to opposition less than a week apart in July 2020. The two giant planets will be spectacular together, staying within a few degrees of each other in the evening sky for the rest of that year. They’ll pass just 0.1° apart at dusk on Dec. 21, 2020, their closest pairing since 1623, during Galileo’s time. I’m looking forward to that rare event, and I hope you and your students will also!

Mars in late May 2016 presented earthbound viewers with a fine opposition and a closest approach. Mars then appeared at magnitude –2.1, slightly brighter than Jupiter at the time. Mars remains in the evening sky for nearly all of school year 2016-2017, but fades as our faster-moving Earth leaves it behind. Mars is still a bit brighter than zero magnitude in south-southwest at dusk in early September 2016; it slightly outshines Arcturus and Vega, the brightest stars then visible. Mars fades to mag. +1.0 by mid-January 2017, when it’s in the southwest at dusk, a few degrees upper left of brilliant Venus. For a few evenings around April 21, 2017, Mars passes within 4° south of the Pleiades star cluster low in west to west-northwest, and glows dimly at mag. +1.6, about as bright as Castor, the fainter of the Gemini twins. Mars passes 6° north (upper right)

of brighter, sinking Aldebaran, eye of Taurus, on May 5, 2017. Around the middle of May, Mars sets as twilight ends. Binoculars may help follow Mars sinking into the twilight glow until early June. Mars is in conjunction with the Sun on July 26, 2017.

By early in September 2017, dim Mars at mag. +1.8 begins to emerge into the eastern morning twilight glow. On the night of July 26, 2018, Earth will overtake Mars, and the red planet will be at opposition, in the sky nearly all night, gleaming at mag. –2.8. Closest approach, within 36 million miles of Earth, occurs four nights later.

Oppositions of Mars occur at intervals of 25 to 27 months, happening each time Earth overtakes Mars: May 22, 2016; July 26, 2018; Oct. 13, 2020; Dec. 7, 2022; Jan. 15, 2025; Feb. 19, 2027; Mar. 25, 2029; May 4, 2031; June 27, 2033; Sept. 15, 2035…  After opposition, Mars remains visible in the evening sky for nearly a year. At intervals of 15 or 17 years, the opposition occurs while Mars is near the perihelion of its orbit. These cases are closer and brighter than all the intervening ones: September 1956, August 1971, September 1988, August 2003, July 2018, September 2035, August 2050…

Mercury remained very low in evening twilight in a poor appearance in July-August 2016. Only its presence near Venus and Jupiter enabled observers with binoculars to find it. The innermost planet’s next evening appearance in late November through mid-December 2016 is only slightly more favorable. Mercury lingers 24° lower right of Venus during Dec. 2-12. The apparition begins as Mercury (mag. –0.5) passes 3.5° south (lower left) of departing Saturn (+0.5) on Nov. 23, but the pair is very low in bright twilight in SW to WSW; use binoculars. Mercury is still of mag. –0.5 when it reaches greatest elongation, 21° from Sun on Dec. 10, and almost as bright when at peak altitude a few days later. Mercury dims to mag. 0.0 by Dec. 17 and fades very sharply thereafter.

Mercury begins its best evening appearance of the 2016-17 school year by March 18, 2017, when the emerging planet shines at mag. –1.3 and appears within 9° left of departing Venus. Mercury climbs to peak altitude in evening twilight on March 31, still bright at mag. –0.2, and at greatest elongation, 19° almost directly above the Sun. This is a very favorable apparition, making Mercury very easy for unaided eye. During April 1-4, Mercury pauses 15° lower right of fainter Mars (+1.5). By April 6, Mercury fades to mag. +1.0. Mercury fades very quickly after that, and within a very few days can no longer be seen. The reason for the rapid fading is that in the planet’s crescent phases, features on its rough surface cast shadows, decreasing the brightness of the illuminated area. Cloud-covered Venus does not suffer such an effect; in fact, Venus appears brightest when it’s a crescent about one-fourth illuminated, about five weeks before and after inferior conjunction.

Planet gatherings and pairings. The recent striking arrangements of Venus, Jupiter, and Mercury, and of Mars, Saturn and Antares, in late August 2016 are described in a separate article. Venus, Saturn, and Antares will form beautiful gatherings during Oct. 26-29. For eight evenings, Jan. 29-Feb. 5, Venus lingers within 5.5° west of Mars; Venus does not overtake the red planet this time and instead will pull away.

The Moon is found near one or more planets in the evening sky on these dates in late 2016: Sept. 2, 3, 8, 9, Oct. 3, 5, 7, 8, Nov. 2, 5, 6, 30, Dec. 2, 3, 4, 5. In the first half of 2017: Jan. 1, 2, 31, Feb. 28, Mar. 1, 14 (late evening), 28, 29, 30, Apr. 10, 27, May 7, 26, June 3, 9, 30.

These events and many others will be illustrated on the Abrams Planetarium Sky Calendar. For information on how to subscribe, visit www.abramsplanetarium.org/skycalendar/.

Robert C. Victor was Staff Astronomer at Abrams Planetarium, Michigan State University. He is now retired and enjoys providing skywatching opportunities for school children in East Lansing, MI and in and around Palm Springs. 

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. 

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 writes an astronomy blog at jeffreylhunt.wordpress.com and can be followed on Twitter at @jeff_hunt.

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Written by Robert Victor

Robert Victor

Robert C. Victor was Staff Astronomer at Abrams Planetarium, Michigan State University. He is now retired and enjoys providing skywatching opportunities for school children in and around Palm Springs, CA. Robert is a member of CSTA.

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