Mohawk Valley Astronomical Society

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Planet Watch 2017

by Perry Pezzolanella

Planetary observing here on the World of Water will be rewarding throughout most of 2017. Venus, Jupiter, and Saturn will keep the observer busy every clear night into November with Jupiter and Saturn competing for attention early in the summer! The night sky can deliver a few surprises with the possibility of an aurora, a strong meteor shower, or maybe the appearance of a bright comet or two. There are always beautiful lunar and planetary conjunctions and countless asteroids, satellites, Iridium flares, and the reliable International Space Station to make for a productive night of observing.

The main event of 2017 will be the partial eclipse of the Sun on August 21. The entire eclipse will be visible locally, if the weather permits. It will be an eerie sight with the Sun 67% obscured by the Moon at its maximum at 2:39 P.M. appearing like an upside down crescent high in the south. The eclipse begins at 1:19 P.M. and ends at 3:54 P.M. There are no lunar eclipses during 2017. It is hoped that several MVAS members will be on the center line elsewhere in the U.S. observing totality. The last successful solar eclipse locally was on Christmas Day 2000 with the Sun 60% eclipsed.

Venus will dominate the evening sky during the opening months of the year as Mars slowly fades into the western twilight by spring. Mercury will briefly come into view later in March just as Venus plunges out of view. Jupiter will already be gaining prominence in the evening by April, and Saturn will compete with it by June and vie for attention all summer. Jupiter will depart into the western twilight soon after Labor Day and Saturn will follow after Halloween. This will leave most of November and all of December barren of any bright planets. Uranus and Neptune will be at their best from September through the end of the year to help fill the void and should not be overlooked even if they are not brilliant planets. Here is the breakdown for each planet in the evening sky during 2017:

Mercury: The World of Ridges may seem challenging to find because it is always so low to the horizon and immersed in bright twilight, but it is easiest to see in the evening from March 18 through April 8, being highest above the horizon on April 1. Mercury grows steadily through this period from 6 to 10 arcseconds across as it approaches Earth, but its magnitude will dim from -1 to +2. It will go through phases like a tiny, coppery version of the waning Moon, from nearly full to a thin crescent.

Venus: The World of Volcanoes will dazzle the winter evenings early this year shining its highest above the western horizon, and will be at its brightest possible at magnitude -4.9 on February 17 before plunging out of view during March as it passes through inferior conjunction, between the Earth and Sun, on March 25. It will grow from a plump half-moon phase around 22 arcseconds across at the start of the year and will swell into a huge, thin crescent nearly one arcminute across by mid-March. Venus’s light will glisten on the newly fallen snow on frigid winter evenings and may be capable of casting shadows on the snow. After conjunction, it will re-emerge into the morning sky for the rest of 2017.

Mars: The World of Deserts has an off year as it spends most of the year on the far side of the Sun, making it too small and dim to seriously observe. It will be a different story by July 2018 when it will have its best opposition since 2003, growing to 24.3 arcseconds across!

Jupiter: The World of Lightning is a favorite as it is always so large and full of changing detail. Opposition occurs on April 7 in Virgo near Spica, with an angular diameter of 43.3 arcseconds across and shining at magnitude -2.5. Jupiter rises in the east during the evening by February, which makes for an excellent opportunity to follow it through one full rotation during the long winter nights as it rotates in less than ten hours while winter nights last more than 12 hours. Jupiter is consistently huge through a telescope making it rewarding to observe and photograph with its various cloud belts and two polar hoods. Even though the challenging Great Red Spot is growing smaller, it is contrasting more with its surroundings and can sometimes be seen. It might be possible to see the tiny discs of the larger moons, Callisto and Ganymede, to watch them transit Jupiter, and to follow their shadows across the giant planet. Jupiter will eventually become lost in the evening twilight by September as it fades to magnitude -2.0 and shrinks to 33 arcseconds across.

Saturn: The World of Rings will be at its best with the rings as wide open as possible and will be the highlight of all star parties during the pleasant warmer nights this summer. The rings will provide plenty of detail with the Cassini Gap being the obvious feature. Saturn is at opposition in southern Ophiuchus on June 15 when it will be 18.4 arcseconds across and shine at magnitude 0. The comfortable summer nights will allow an excellent opportunity to study its belts and spots, and to look for the Cassini Division in the rings. The largest moon, Titan, is usually visible, shining about 8th magnitude. Saturn will slowly fade to magnitude +0.6 and shrink to around 16 arcseconds across in November when it becomes lost in the evening twilight.

Uranus: The World of Smog will be at opposition on October 19 in Pisces. Uranus will be 3.7 arcseconds across and shine at magnitude +5.7 not far to the west of the bright star Omicron Piscum making it easy to locate again this year. Uranus rises before midnight by September and gradually fades into the evening twilight by April 2018.

Neptune: The World of Wind is at opposition on September 5 in Aquarius below the Water Jar and very close to the bright star Lambda Aquarii making another excellent year to locate and observe it. Neptune will be 2.4 arcseconds across and shine at magnitude +7.8. Neptune will rise before midnight by August and disappear into the evening twilight during February 2018. A finder chart for Uranus and Neptune will appear in the August issue of Telescopic Topics.

Pluto: The World of Glaciers is now a familiar world full of discoveries and new mysteries. Pluto is at opposition on July 10, just east of the Teaspoon asterism of Sagittarius among thousands of stars and will shine like a faint spark at magnitude +14.2. It will be only 0.1 arcseconds across making it a challenge to find. Pluto is exiting the heart of the Milky Way, making the task of confirming it perhaps a touch easier, but it will steadily dim to magnitude +15 by 2050, and its increasingly southerly declination, now nearly -22º, will forever keep Pluto as the ultimate observing challenge.