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Star Points: May offers opportunity to observe Jupiter and its moons

Star Points: May offers opportunity to observe Jupiter and its moons
Jupiter floats in the foreground as part of the Astro Adventure which was held at the Maryland Science Center. (Algerina Perna / Baltimore Sun)

May is one of my two favorite months for observing; the other is September. That is because in the mid-Atlantic region these seem to be the two months of the year with more clear nights than every other month. The weather dries out and the sky is clear and cloud free from zenith to horizon.

The main planetary body for this month is giant Jupiter. It reaches opposition on May 9 meaning it is up all night. It rises at sunset, transits at local midnight (1 a.m. Daylight time) and sets at sunrise. At opposition Jupiter shines at magnitude -2.5.

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Use a small telescope or binoculars to see Jupiter's four "Galilean" satellites — Ganymede, Io, Europa and Callisto. There are dozens of other moons, but these are the only ones visible in small telescopes. To see any more requires a moderate-to-large telescope and a good finder chart or software to predict where to look.

The brightness of the Galilean satellites is roughly between magnitudes 5 and 6 and theoretically bright enough to be seen with the naked eye whose limiting magnitude is usually stated as being mag. 6. However, the glare from nearby bright Jupiter dazzles the eye thus making them impossible to see with the naked eye. Some people however have reported success in observing them that way by blocking out Jupiter with an object — for instance, the tip of a ballpoint pen. I have never had any such luck myself. Without a doubt, near perfect vision is required.

A small telescope will reveal the darker brownish-red bands and lighter cream-colored zones in the clouds of Jupiter. The bands and zones all appear parallel to each other and to Jupiter's equator.

Later at night, two more naked eye major planets, Saturn and Mars, appear in the eastern sky in the pre-dawn hours. By mid-month Saturn is nearly due south at morning twilight with Mars following to the east. Mars will be about one magnitude brighter than Saturn — magnitudes -0.5 and +0.5, respectively.

On Saturday, May 12 members of the Westminster Astronomical Society will have telescopes at Bear Branch Nature Center (BBNC) for observing during and after the 7:30 p.m. planetarium program. There is no charge for the observing and it is free. Planetarium reservations can be made by calling Carroll County Recreation and Parks at 410-386-2103. The planetarium show is $5 per individual.



Curtis Roelle is a member of the Astronomical Society. His website is www.starpoints.org, and he can be reached atstarpoints@gmail.com.

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