In recent nights, there was a bright light that drew attention to itself low in the eastern sky around 19:30 local daytime. It shines with an even silvery glow and after a couple of hours, when it has risen noticeably higher in the east-southeast part of the sky, it seems to attract attention.
Of course, this would make some sense, because you are looking at an object named after the king of the gods as well as the king of the planets: Mighty Jupiter.
And it marks a pretty auspicious week because we’ll see Jupiter as big and bright as it can be from our earthly vantage point as it approaches perihelion: the point in its 12-year orbit that places it closest to the Sun. .
On the subject: Jupiter approached Earth in 59 years, NASA reports
Jupiter now appears 11% larger and more than 1.5 times brighter than it was in April 2017, when it was near aphelion (the farthest point in its orbit from the Sun). Even 7x binoculars will show Jupiter as a tiny disk. A small telescope will do a much better job, while in larger instruments Jupiter can be seen in a series of reds, yellows, tans, and browns, as well as many other telescopic features. Amateur astronomers have been photographing this large planet all summer as it approaches Earth. The opposition, when it will be in the sky all night, from sunset to sunrise, occurs on Monday (September 26).
At 10:00 pm ET Sunday (September 25), Jupiter will make its closest approach to Earth since 1963. Then he will be at a distance of 367,413,405 miles (591,168,168 km). It may not seem quite “close”, but Jupiter is so large and bright that not only is it easy to see with the naked eye, but in a small telescope that magnifies only 36 times, it appears to the naked eye as big as the Moon. .
(Image credit: Haitong Yu/Getty Images)
Giant among giants
Jupiter has a diameter nearly eleven times that of Earth and is 88,846 miles (142,984 km) wide. It takes almost 12 years to complete one trip around the Sun. But if Jupiter’s year is long, then its day is short. A large planet makes one revolution in just under 10 hours. For a planet of this size, this rate of rotation is astonishing. A point on Jupiter’s equator moves at 22,000 miles per hour, compared to 1,000 miles per hour for a point on Earth’s equator. This high rate of rotation gives Jupiter the appearance of a slightly flattened ball. It has a rocky core surrounded by a thick mantle of metallic hydrogen, wrapped in a massive atmospheric cloak of colorful clouds of ammonium hydrosulfide.
Jupiter is a huge giant planet, more than twice the mass of all seven other planets combined. It has one of the most mysterious spots on the surface of any planet: the Great Red Spot, which appears and disappears unpredictably and has a width equal to the Earth. There is also some evidence that Jupiter loses more heat energy to radiation than it receives from the Sun, and so it can produce energy of its own, an activity usually more characteristic of a star than a planet.
(Image credit: NASA)
Jupiter also has a faint ring system, although unlike Saturn’s famous rings, which are highly reflective because they are made of ice, Jupiter’s rings are mostly made up of many tiny dust particles.
Like Earth, Jupiter has a magnetic field; the vast donut-shaped belt of electrically charged particles that surrounds the planet—a ring similar to the Van Allen belts of charged solar particles held together by the Earth’s magnetic field.
Dance of the moons
Let’s not forget about the four main satellites of Jupiter, discovered 412 years ago by Galileo. This is a telescopic treasure. The four – Io, Europa, Ganymede and Callisto – run in a fun race with each other and revolve around Jupiter so quickly (1.68 days for Io and 16.7 days for Callisto) that they change their appearance from hour to hour and night towards night, casting their shadows across the planet, disappearing behind its giant disk or sinking into its shadow.
On Sunday (September 25), for example, you will be able to see three moons on one side of Jupiter (Io, Europa and Callisto) with a fourth moon (Ganymede) on the other side. On Monday (September 26), Europa and Io will join Ganymede; now Callisto will be alone on the other side of Jupiter. Finally, on Tuesday (September 27) you will see two moons on one side (Europa and Ganymede) and two (Io and Callisto) on the other.
In fact, on Wednesday (September 28) at 00:08 ET (27:08 PT September 27), Ganymede will pass in front of Jupiter, which is called a transit. In addition to the Big Four, Jupiter has 76 other moons. Many of them are exceptionally small and were discovered thanks to space probes that passed near Jupiter during the decades of the 1970s, 80s and 90s.
When Jupiter appears high in the sky, some may appear to move in a circle or spiral. Over the years, I’ve received emails from people who claimed to have seen Jupiter do just that: move forward and backward.
So why does it seem to be moving? It is likely that those who saw this strange movement experienced an autokinetic effect. This is a phenomenon of human visual perception in which a fixed small point of light in a dark or featureless environment appears to be moving. Many UFO sightings are also explained by the autokinetic effect on stars or planets. Psychologists explain the perception of movement where it is not, “small involuntary movements of the eyeball.” The autokinetic effect can also be enhanced by the power of suggestion: if one person reports that light is moving, others are more likely to report the same.
Jupiter is currently shining in the constellation Pisces, a star pattern made up mostly of dim stars. Under clear dark skies and no moon, Jupiter will shine with little or no competition from other nearby stars. If a person constantly looks at Jupiter for about 15 to 30 seconds, it is possible that an autokinetic effect will kick in, causing Jupiter to rotate or perhaps describe a small circle.
Try looking at Jupiter in the late evening hours this week and see if it moves for you.
If you want to see a great view of Jupiter at opposition, don’t miss our guide to the best binoculars and the best telescopes to spot Jupiter or other objects in the night sky. For the best shots of Jupiter, check out our recommendations for the best cameras for astrophotography and the best lenses for astrophotography.
Editor’s Note: If you have photographed Jupiter and would like to share it with Space.com readers, please send your photos, comments, your name and location to spacephotos@.
Joe Rao is an instructor and guest lecturer at the Hayden Planetarium in New York. (will open in a new tab). He writes about astronomy for Natural History magazine. (will open in a new tab)Farmer’s Almanac (will open in a new tab) and other publications. Follow us on Twitter @Spacedotcom (will open in a new tab) and on facebook (will open in a new tab).