Polka Dots And A Suicidal Planet

The waxing first quarter moon will shine very close to Antares Thursday evening in twilight. This map shows them at around 8:30-9 p.m. as you look southwest. Created with Stellarium.

The moon will cover the star Antares, the bright red-colored star in Scorpius this afternoon for the Northern Minn.-Wis. region at about 4:05 p.m. Two things will make this nearly impossible to see: bright daylight and the moon’s low elevation above the southeast horizon. Skywatchers on the East Coast will have a better chance of seeing the event, called an occultation, through binoculars, or preferably a small telescope, where the moon is higher up.

No matter. The star-moon combo will still be very close together after sunset so keep a lookout for them in the southwestern sky. Many of us get a little thrill to see two bright celestial bodies so close together.

Jupiter wore spots last night (Aug. 26) before midnight. These drawings of the planet’s cloud belts and moon shadows were made using a 10-inch reflecting telescope at 250x. "G" stands for the moon Ganymede; "E" for Europa. These two moons and the shadows they cast on Jupiter’s clouds made for a wonderful night of planet viewing. In the right drawing, notice how white Europa appears compared to grey Ganymede. Credit: Bob King

I got an unexpected thrill last night when I pointed my telescope at Jupiter. Polka dots! The equatorial region of the planet was spotted with the shadows of two moons — Europa and Ganymede — and the little grey disk of Ganymede itself. When a moon passes in front of Jupiter and casts a shadow, astronomers call it a shadow transit. Ganymede, the largest of Jupiter’s four bright moons, casts the biggest shadow. You can easily see it in a very small telescope.

The moons Europa (left) and Ganymede taken by the Voyager and Galileo spacecraft. Europa’s icy crust makes it one of the most reflective moons in the solar system. Ganymede, which is made of a mixture of rock and ice, is considerably darker. Photos: NASA

What was even more amazing was spotting the tiny white disk of Europa as it neared the inside edge of the planet around 11:30 p.m. It was clearly white in contrast to Ganymede, a testament to its icy surface. It blows me away that even modest telescopes can see such things nearly half a billion miles away. It helped that the air was very steady which allowed the sharpest, clearest views of the planet in a long time.

The show didn’t end there. The moon Io popped into view around 11:30 after being eclipsed by Jupiter, and by 12:15 both Ganymede and Europa had departed the disk and sparkled in the dark alongside the planet. Not even Jimmy Fallon could touch this kind of entertainment.

I would posted news of this freckled frenzy in advance but I wasn’t paying as close attention to the comings and goings of Jupiter’s moons as I should have. The next time Ganymede and Europa cross in front of the planet at the same time will be after midnight on September 3. Please visit back next week when I’ll post details.

WASP-18b is so close to the star WASP-18 that it completes one orbit around it in less than a day. Credit: Picture courtesy ESA, NASA, M. Kornmesser (ESA/Hubble), and STScI

There have been more than 370 planets discovered outside the solar system. One of the most recent was picked up by Coel Hellier, a professor of astrophysics at Keele University in England. Called WASP-18b (named after the Wide Angle Search for Planets), this latest find is 10 times bigger than Jupiter and only 1.4 million miles from its star. That’s so close that the star’s powerful tidal forces — think of the moon pulling on the Earth to create the tides — are causing the planet to slowly spiral down into the star. Scientists calculate that this "giant Jupiter" has only a million years to live before it’s fried to a marshmallow crisp. WASP-18b is 325 light years away in the southern constellation of the Phoenix. Learn more about fated world here.