Sky Watch: Jupiter is on the night shift

Have you seen that super bright star rising in the low southeastern sky shortly after sunset in the evening twilight? It’s not a star, but rather the big guy of our solar system, the planet Jupiter.

The 88,000-mile wide planet, named after the king of the gods in Roman mythology, is not only visible all night long right now, it’s also at its closest approach to Earth for 2018, at just under 410 million miles. Actually, though, it’s Earth and Jupiter approaching each other in their respective orbits around the sun.

Just a few nights ago, Jupiter reached what astronomers call “opposition.” It’s dubbed that because Jupiter and the sun are more or less at opposite ends of the sky and the Earth lies between them, as you can see in the diagram. Since they’re at opposite ends of our celestial dome the sun sets in the west as soon as Jupiter rises in the east, and vice versa, just like a full moon. The Jovian giant is prowling across the sky all night long for our perusal!

(Courtesy of Mike Lynch)
(Courtesy of Mike Lynch)

You can also see that geometrically Jupiter and the Earth are at their minimum distance from each other. Earth and Jupiter get into the opposition position every 399 days, or a little more than every 13 months. That’s because it takes Earth slightly over 365 days to make one complete orbit of the sun, while it takes Jupiter 12 years to make its much larger solar circuit. So in the year that it takes Earth to circle the sun, Jupiter has only made it a twelfth of the way around the home star of our solar system. As a result, it takes the Earth a little over a month to be in position where it’s once again in line between the sun and the king of the planets.

If you have super eagle eyes, there are times when Jupiter looks like it has tiny appendages on either side of it. These are Jupiter’s moons. There’s no way you can visually resolve them with the naked eye, no matter how good your eyesight is, but even a pair of small binoculars will reveal up to four of Jupiter’s brightest moons, which look like little stars on either side of the great planet. I’ll have much more on Jupiter’s moons and how to keep up with them in next week’s Skywatch column.

With a small telescope, you can easily see Jupiter’s moons, but you also can clearly resolve the disk of the planet and some of the cloud bands and zones that stripe the big guy of the solar system.

Jupiter is mostly just a big ball of hydrogen and helium gas, but in its outer atmosphere there’s methane, ammonia, sulfur and other gases that create the multicolor cloud bands. Two darker cloud bands on either side of Jupiter’s equator are the easiest ones to spot.

There are also storms circulating in Jupiter’s upper atmosphere. The biggest one is known as the Great Red Spot, and it is three times the diameter of our Earth. This giant hurricane-like storm has been raging on Jupiter for hundreds of years. Despite its moniker, the Great Red Spot isn’t all that red — more like a pale pink. Unless you have a moderate to large telescope and super clear conditions, it’s hard to spot it in Jupiter’s southern hemisphere. What also makes it tough to see is that it’s not always visible because of Jupiter’s rapid rotation. Jupiter whirls around on its axis once every 10 hours, so half of the time the Red Spot is facing away from us.

A really handy website I like to use to find the Red Spot is from Sky and Telescope magazine. You can find the times the Red Spot will transit Jupiter, which is the time it can be found in the middle of the planet and skewed just to the south of the center point, nestled in the darker equatorial cloud band. Remember that most telescopes give you a reverse-upside-down view, so in that case you’ll look a little above the center of Jupiter’s disk. Seeing that pale pink storm is definitely a stargazing challenge.

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