Maybe you’ve already noticed that bright star low in the southeastern sky around bedtime. That’s Jupiter, the biggest planet and a welcome sight in the evening sky. For months now, Mars has been the only planetary presence, and it’s been fading away in the west like a cooling ember. Jupiter has come to save the day as it does once every 13 months when it lines up with the Earth and sun at opposition.
That’s when the two planets are paired up on the same side of the sun and closest to one another. Closest also means brightest. Jupiter will shine at magnitude –2.6, about the same brightness as a good pass of the International Space Station.
Because Jupiter’s on one side of the Earth and the sun on the other, we see them in opposite parts of the sky, hence the term. Opposition occurs on June 10. On that day, the big planet will rise in the east just about the same time the sun sets in the west and toot its horn all night long.
Jupiter resides for now in Ophiuchus the serpent-bearer, sometimes dubbed the 13th zodiac constellation. There are officially 12, but when constellation boundaries were set in 1930, Ophiuchus (oh-fee-YOU-cuss) was extended south to include the ecliptic, the path of the planets and sun. That path is what defines the zodiac, the belt of constellations familiar from the daily horoscopes.
It departs Ophiuchus on Nov. 16 when it crosses the border into Sagittarius the archer. If you can reach dark skies you’ll find Jupiter glaring from a particularly dark splotch of sky called the Great Dark Horse. That’s no hole but multiple massive clouds of star dust shaped like a horse reared up on its back legs silhouetted against the starry Milky Way. It’s faintly visible to the naked eye and a fine sight in wide-field binoculars.
Through steadily-held 10x binoculars you can make out from one to four of Jupiter’s brightest moons called the Galilean satellites because they were first seen by the old Italian himself. The reason the number varies is because sometimes a moon will pass in front or behind the planet and hide from view. They look like tiny stars in a line very close to and on either side of the planet. A small telescope gives a much better view plus the image is steady and not bouncing up and down with every heartbeat.
That same small scope will also show the most prominent cloud belts — the North and South Equatorial Belts — as two parallel stripes on either side of Jupiter’s equator, and you might even catch the shadow cast on the clouds by the largest moon, Ganymede, when it passes in front of Jupiter, called a transit. All we see of Jupiter is atmosphere. No surface. Deep down there’s probably a ball of rock a couple times the size of the Earth beneath a thick shell of hydrogen gas compressed so strongly it behaves like a metal.
A 6-inch or larger telescope will clearly show the planet’s best known feature, the Great Red Spot (GRS), a hurricane of sorts more than twice the size of the Earth that’s been whirling around near the south edge of the South Equatorial Belt for centuries. Because Jupiter is rather low in the sky this season for northern hemisphere skywatchers it’s more affected by atmospheric turbulence. The other morning I got up to view the GRS but the planet was total mush and I could barely make it out in the unsteady air.
To see details on planets you have to be persistent and foray into as many clear or partly cloudy nights as possible — even for just 10-15 minutes — in hopes of catching that perfect one where the air is still and the planet looks as sharp and present as the hand in front of your face. In an earlier blog I described how the Red Spot appears to be shedding material called “flakes” over the past month or so.
Capable astrophotographers have recorded all these transformations in great detail; to see them visually you’ll need an 8-inch or larger telescope and a sharp, steady view.
But you can see the Spot itself, its lovely reddish-orange hue and the long, dark cloud cloud bands that extend out in front of it. Other belts and zones (the brighter areas between the dark belts) will be visible, too. Plus you can watch moons disappear as they’re eclipsed by Jupiter’s shadow and hover like pearl earrings along the planet’s edge before and after transits and occultations.
Here are some resources for you:
GRS transit calculator. Just enter a date and you’ll get the times of the next three transits of the Red Spot for your time zone. That’s when it faces you squarely. You can easily see it an hour or so before the transit time and an hour after.
Phenomena of Jupiter’s Moons. Download this pdf that lists all of the eclipses, transits and occultations of Jupiter’s moons for 2019. Times are 24-hour format and given for Greenwich (England). Subtract 4 hours for Eastern Daylight; 5 hours for Central; 6 hours for Mountain and 7 hours for Pacific. Or just use the Jupiter Moons Observing Tool to see where the moons are and what events are happening for a particular night for your zone
Observing Jupiter is alway so much fun because it’s a planet with a lot of weather which means a lot of changes can happen to its clouds and storms in a relatively short time — just like on Earth! Even just watching the moons dance around in the smallest of scopes is a joy.