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Planets offer easy, enjoyable viewing targets

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Friday, June 8, 2018 10:09 PM

Greetings, Stargazers.

This will be a good summer for planet watching. At most star parties, the planets are considered dusk objects because they can successfully be seen before it is really dark. I must admit that I typically rush the planets in order to point my telescope at more distant nebulae and galaxies. So this month, I will try to rectify my neglect of the planets and give you a rundown of some things you can expect to see.

Because the planets are brighter than most other things in the sky, they are among the easiest to find and keep track of. Using your naked eyes, you can track the motion against the background stars from night to night. You should also be able to note the sometimes-dramatic variations in brightness from month to month. As with many things celestial, binoculars or telescopes can show you even more.

Mercury is the planet that may best be viewed with your naked eye. Being closest to the sun, it comes and goes rather quickly as an evening or morning star. It is small and without an atmosphere, so its surface looks quite a bit like our moon. However, it is so small that even the best Earth-based telescopes can’t show any of this surface detail.

Venus is totally covered with clouds that make it a dazzling white through binoculars or telescopes. As such, you won’t see any surface detail and don’t expect to keep your night vision after a Venus view through a telescope. The interesting thing about a magnified Venus is the rather obvious phase. Like the moon, Venus goes through a waxing and waning cycle of crescent and gibbous phases as it completes its orbit. Right now, Venus is in a waning gibbous phase as it gets closer to Earth in its orbit.

Mars is often a disappointment when seen for the first time through a telescope. It is relatively small, and most small telescopes can’t show much surface detail. However, the polar ice caps can be startlingly white, and patient viewing with high magnification (greater than 100x) can reward the viewer with subtle details. I should let each individual decide if their imagination lets them see canals or not. This year provides the closest view since 2003, and later this summer, Mars will shine brighter than Jupiter.

Jupiter is always a great telescope target. Even though it is more than 10 times as far away as Mars, it is more than 20 times its diameter so always appears bigger in a telescope. The Galilean moons Io, Europa, Ganymede and Callisto change their positions noticeably from hour to hour so there is always a different view. These moons are easily visible through binoculars. Cloud bands on the surface of Jupiter are visible in even the smallest telescopes. An 8-inch telescope can show more cloud bands and more surface details, such as the “great red spot,” even though you are likely only to see it as a “pale beige spot.” Don’t expect to see any of the colors you see in photographs unless you get a chance to view Jupiter through a 16-inch-or-larger telescope.

Saturn can’t help but be everyone’s favorite target. Even binoculars can show that Saturn doesn’t look round, and the smallest telescopes can show the space between the planet and the rings. Larger telescopes can show one or more gaps within the rings. Because of its current position in its orbit, this year Saturn will never get more than about 30 degrees above the southern horizon. That is its lowest high point in many years.

This monthAt dusk, Venus and Jupiter will be competing for your attention. When looking south, they will be symmetrically positioned to your left and right and will be visible long before any other stars. At 9:30 p.m., Venus will be 30 degrees over the western horizon, and Jupiter will be 30 degrees over the southeastern horizon.

Later this month, Mercury will be visible as an evening star in the west, below and to the right of Venus, but much dimmer.

Saturn rises with the Milky Way a little before 11 p.m. and will be near the teapot asterism of Sagittarius. It will be at opposition, its closest approach to Earth, on June 27.

Mars is now already brighter than any star, but it doesn’t rise until almost 1 a.m. Every night, it will get slightly brighter and rise slightly earlier as it approaches its opposition next month.

Charles Hakes teaches in the Physics and Engineering Department at Fort Lewis College and is the director of the Fort Lewis Observatory. Email him at hakes_c@fortlewis.edu.

Useful links

Size and distance to the planets: https://bit.ly/2M2oOEK.
Astronomy picture of the day: http://apod.nasa.gov/apod/.
An astronomer’s forecast for Durango: https://bit.ly/2eXWa64.
Old Fort Lewis Observatory: www.fortlewis.edu/observatory.
Four Corners Stargazers:
https://bit.ly/2eUqRJX.https://bit.ly/2iGQPTb.https://bit.ly/2igOSMc.

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