Return to Newsletter Index

Planet Watch 2018

by Perry Pezzolanella

This will be another excellent year for planetary observing with the best time being during the warmer months. Venus, Mars, Jupiter, and Saturn will keep observers busy every clear evening from February into October. All four planets will be very bright and compete for attention, perfect for star parties! The night sky is notorious for delivering 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 especially with Venus and the crescent Moon this year, along with countless asteroids, satellites, and the International Space Station to make pleasurable nights of observing.

The main event of 2018 will be an impressively close approach of Mars this summer for the closest since the historic 2003 opposition. A slight partial lunar eclipse will be visible before sunrise on January 31 in the brightening twilight before the Moon sets. The next total lunar eclipse will occur during the night of January 20-21, 2019; the next solar eclipse will be a deep partial occurring on June 10, 2021 at sunrise with the Sun rising as a stunning crescent around 83% eclipsed.

There will be a quiet start to the new year with Uranus slowly sinking into the twilight glow by March just as Venus reappears. Mercury makes its best evening appearance in the west after sunset in March. Jupiter will be climbing higher earlier in the evening in April and will be joined by Saturn in May, and Mars in June. Mars will actually outshine Jupiter during July and August, which will be quite a sight to see! Venus will join the trio earlier in the evening low in the west, but it will still be worth observing before it sinks into the western twilight along with Jupiter during October. Saturn will linger into November before leaving Mars behind as the lone sentinel of the lengthening evenings as Christmas approaches. Uranus and Neptune will be at their best from September through the end of the year and should never be overlooked even if they are not brilliant planets. Here is the breakdown for each planet in the evening sky during 2018:

Mercury: The Swiftest World 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 1-22, being highest above the horizon on March 15. It will be unusually easy to find in early March as it will be very close to dazzling Venus. 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 Hottest World will become visible low after sunset during February and remain dismally low and difficult this year with it being highest above the western horizon on August 17. Venus will be at its brightest at magnitude -4.5 before plunging out of view during October as it passes through inferior conjunction, between the Earth and Sun, on October 26. It will grow from nearly full in May to a crescent by August and continue to swell into a huge, thin crescent over one arcminute across by late-October.

Mars: The Dustiest World will finally be at its best since 2003 when it reaches opposition on July 28, but due to its highly elliptical orbit, it will be closest to Earth on July 31 when it will be an impressive 24.3 arcsecond across and blaze at magnitude -2.8 in Capricornus. It should be possible to see the bright south polar ice cap and dusky surface features as long as the dust storms stay away. Mars will steadily shrink to less than 8 arcseconds across and grow dimmer than magnitude 0 by Christmas as it slowly sinks in the west well into 2019.

Jupiter: The Largest World is at opposition on May 9 in Libra, with an angular diameter of 43.8 arcseconds across and shining at magnitude -2.5. Jupiter rises in the east during the evening by March and is consistently huge through a telescope making it rewarding to observe and photograph with its various cloud belts and two polar hoods. The Great Red Spot can be challenging, but can sometimes appear quite obvious depending on the brightness of the clouds near it. It might be possible to see the tiny discs of the larger moons, Callisto and Ganymede, and watch them and their shadows transit Jupiter. The largest planet will become lost in the evening twilight by October as it fades to magnitude -2.0 and shrinks to 33 arcseconds across.

Saturn: The Prettiest World is at its best once again in 2018 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 Sagittarius on June 27 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 around 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 Murkiest World will be at opposition on October 23 in Pisces. Uranus will be 3.7 arcseconds across and shine at magnitude +5.7 to the east of the bright star Omicron Piscium making it easy to locate again this year. Uranus rises before midnight by September and gradually fades into the evening twilight by April 2019.

Neptune: The Windiest World is at opposition on September 7 in Aquarius below the Water Jar and east of the bright, golden star Lambda Aquarii, which will help 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 2019. A finder chart for Uranus and Neptune will appear in the August issue of Telescopic Topics.

Pluto: The Coldest World is now a known world of fascinating landmarks. Pluto is at opposition on July 12, just east of the Teaspoon asterism of Sagittarius among thousands of stars and will shine like a faint spark at magnitude +14.3. It will be only 0.1 arcseconds across making it a challenge to find, but it is slowly exiting the heart of the Milky Way, making the task of confirming it perhaps a touch easier.