For the past few nights, there has been a bright light that drew attention to itself low in the eastern sky around 7:30 p.m. local time. It shines with a constant silvery glow and a few hours later, when it has climbed noticeably higher in the east-southeast part of the sky, it seems to command attention.
Of course, that would make sense because you’re looking at the object named after the King of the Gods and also the King of the Planets: Mighty Jupiter.
And this marks a rather auspicious week, as we’ll see Jupiter looming as big and bright as possible from our Earth vantage point, as it approaches perihelion: that point in its 12-year orbit that puts it closest to the sun. .
Related: Jupiter has been closest to Earth for 59 years, according to NASA
Jupiter now appears 11% larger and more than 1.5 times brighter than in April 2017, when it was near aphelion (the farthest point in its orbit from the sun). Even permanently held 7-power binoculars will show Jupiter as a small disk. A small telescope will do much better, while in larger instruments Jupiter resolves into a series of red, yellow, beige, and brown hues, along with a host of other telescopic details. Amateur astronomers photographed this large planet all summer as it approached Earth. The opposition, when it will be in the sky all night, from sunset to sunrise, occurs on Monday, September 26.
At 10 p.m. Eastern Time on Sunday, September 25, Jupiter will make its closest approach to Earth since 1963. It will then be 367,413,405 miles (591,168,168 km) away. It might not look exactly “close”, but Jupiter is so big and bright that it’s not only easily visible to the naked eye, but through a small telescope magnifying only 36 times it appears as big as the moon. with the naked eye. .
A giant among giants
Jupiter has a diameter nearly eleven times that of Earth at 88,846 miles (142,984 km) wide. It takes almost 12 years to make a trip around the sun. But if Jupiter’s year is long, its day is short. The large planet rotates once in just under 10 hours. For a planet of this size, this rotation speed is incredible. A point on Jupiter’s equator moves at a speed of 22,000 mph compared to 1,000 mph for a point on Earth’s equator. This rapid rotational speed gives Jupiter the appearance of a slightly flattened ball. It has a rocky core enclosed in a thick mantle of metallic hydrogen enveloped in a massive atmospheric mantle of multicolored clouds of ammonium hydrosulfide.
Jupiter is a giant giant of a planet, with a mass more than twice that of the other seven planets combined. It has one of the most mysterious flaws on the face of any planet: the great red spot that comes and goes unpredictably and is as wide as Earth. There is also evidence that Jupiter loses more thermal energy to radiation than it gains from the sun, and therefore can produce its own energy – an activity generally more characteristic of a star than a planet.
Jupiter also has a faint ring system, although unlike Saturn’s famous rings which are highly reflective because they are made up of ice, Jupiter’s rings are mostly made up of a myriad of tiny dust particles.
And like Earth, Jupiter has a magnetic field; a vast doughnut-shaped belt of electrically charged particles that encircles the planet – a ring similar to Van Allen’s belts of solar charged particles held captive by the Earth’s magnetic field.
The dance of the moons
Let’s not forget the four main moons of Jupiter, which were discovered 412 years ago by Galileo. They are a telescopic treasure. The four – Io, Europa, Ganymede and Callisto – joyfully race among themselves and orbit Jupiter so rapidly (1.68 days for Io to 16.7 days for Callisto) that they change appearance from hour to hour and from night to night, casting their shadows on the planet, disappearing behind its giant disc, or plunging into its shadow.
On Sunday (September 25) for example, you may see three moons on one side of Jupiter (Io, Europa, and Callisto) with the fourth moon (Ganymede) all alone on the other side. On Monday (September 26), Ganymede will be joined by Europa and Io; 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, at 12:08 a.m. EDT on Wednesday, September 28 (9:08 p.m. PT on the 27th), Ganymede will appear to cross in front of Jupiter, known as a transit. In addition to the “Big Four”, Jupiter has 76 other satellites. Many of them are exceptionally small and were discovered by space probes that passed close to Jupiter during the decades of the 1970s, 1980s and 1990s.
When Jupiter appears high in the sky, it may appear to some to be moving in a circle or spiral. Over the years, I’ve received emails from people who claim to have seen Jupiter do just that: go back and forth.
So why does it seem to move? Those who saw this strange movement probably felt the autokinetic effect. It is a phenomenon of human visual perception in which a small, stationary point of light in an otherwise dark or featureless environment appears to move. Many UFO sightings have also been attributed to the action of the autokinetic effect on stars or planets. Psychologists attribute the perception of movement where there is none to “small involuntary movements of the eyeball”. The autokinetic effect can also be enhanced by the power of suggestion: if one person signals that a light is moving, others will be more likely to report the same.
Currently, Jupiter shines in the constellation Pisces, a star pattern composed mostly of faint stars. Under a clear, dark sky with no nearby moon, Jupiter will appear to shine with little or no competition from other nearby stars. If a person is constantly staring at Jupiter over a period of 15-30 seconds, it is quite possible that the autokinetic effect will kick in and cause Jupiter to spin or perhaps go in a small circle.
This week, late evening, try looking at Jupiter and see if it moves for you.
If you want an unobstructed view of Jupiter in opposition, don’t miss our guides to the best binoculars and best telescopes for spotting Jupiter or other objects in the night sky. To capture the best images of Jupiter you can, check out our recommendations on the best cameras for astrophotography and the best lenses for astrophotography.
Editor’s note: If you take a photo of Jupiter and would like to share it with Space.com readers, send your photo(s), comments, and name and location to firstname.lastname@example.org.
Joe Rao is an instructor and guest speaker at New York’s Hayden Planetarium (opens in a new tab). He writes on astronomy for natural history journal (opens in a new tab)the Farmers Almanac (opens in a new tab) and other publications. Follow us on twitter @Spacedotcom (opens in a new tab) and on Facebook (opens in a new tab).