You may have noticed that Jupiter is particularly bright as of late. It's about to get brighter. Today, March 8, look up at the night sky, and you'll see Jupiter as close to the Earth as it's going to get this year. From our vantage, it will be opposite the Sun and thus in full sunlight. To understand what this means, consider a full moon as an analog: the reason the Moon is full is because it is in full sunlight. Think of Jupiter at opposition as being a "full Jupiter." (Here is a visual representation of the current positions of the planets in our solar system.)
With even a modest telescope, you might be able to make out Jupiter's bands of brown, tan, and white. Sky & Telescope offers a detailed viewing guide for Jupiter, noting that the gas giant "is thrilling to view in just about any telescope. Even a small department-store refractor will reveal several cloud belts and its four brightest moons."
As you gaze upon the gas giant, you can consider some fascinating facts about how we've closed the distance between it and us—and how we're making a return visit this summer. Read on.
A BIG PLANET WITH AN OUTSIZED ROLE IN PROVING GEOCENTRISM WRONG
Jupiter is the first planet beyond the asteroid belt. It is by far the largest known planet in the solar system, and could fit 1000 Earths inside of it. The planet was instrumental in obliterating the notion of the Earth as the center of the solar system. In 1610, after improving his telescope, Galileo Galilei discovered four moons orbiting Jupiter. (Io, Europa, Ganymede, and Callisto are referred collectively as the "Galilean moons.") Evidence of celestial bodies orbiting something other than the Earth was a massive revelation, and ultimately dealt a death blow to the geocentric model of the universe.
In 1632, Galileo published Dialogue Concerning the Two Chief World Systems, which purported to "teach the debate," though was pretty obviously pro-heliocentric. (He wasn't exactly subtle. A character named Salviati argues in favor of a heliocentric solar system first put forth by Copernicus. A character named Simplicius—a play on "simple-minded"—supports a geocentric model.) The Catholic church was not amused, and the following year, the Inquisition tried Galileo for heresy. He spent the last nine years of his life under house arrest. One hundred years later, the church removed Dialogue from its list of banned books, and in 1992—some 359 years after the fact—a Vatican science panel said they regretted the error.
JOURNEYS TO JUPITER THEN & NOW
NASA has been sending spacecraft to study Jupiter since the 1970s. The first spacecraft to reach Jupiter was Pioneer 10 in 1973, the first of four Jupiter flyby missions. (It was also the first spacecraft to reach the outer solar system, where Jupiter orbits the Sun.) Though NASA lost contact with Pioneer 10 in 2003, it remains headed in the general direction of Aldebaran, the red eye of the constellation Taurus, and will reach the eye in 2 million years.
In the late 1970s, NASA returned to Jupiter as part of the Voyager program to the outer planets. It was a once-in-a-175-year opportunity. Jupiter, Saturn, Uranus, and Neptune were in rare alignment. The original plan called for two Voyager spacecraft to explore Jupiter, Saturn and their moons on a five-year mission, and in this endeavor they were wildly successful, discovering new rings around Jupiter and active volcanoes on its moon Io, and enhancing our understanding of Jupiter’s giant red spot. New programming developed after launch then allowed the missions to reach Uranus and Neptune. The spacecraft are still going, with Voyager 1 having recently crossed into interstellar space, placing it beyond the solar winds released from the Sun. It is the first spacecraft to achieve this. (Voyager 2 should arrive in interstellar space this year.)
In 1989, NASA launched the Galileo spacecraft, which would go on to unlock many mysteries of the Jovian system, discovering an immense "interplanetary dust storm"; a new radiation belt above Jupiter; 400-mph winds on Jupiter; a high abundance of helium—as much as can be found on the Sun!—and low occurrences of water in the atmosphere.
These exploration efforts are only the beginning. In July, the NASA spacecraft Juno will enter Jupiter's orbit after a five-year journey. The mission's goals are to work out how Jupiter formed, determine the nature of its core, and try to figure out how it generates such a massive magnetic field. It is the first solar-powered spacecraft to be used for an outer planets mission; previous missions used nuclear power. In January, it set a distance record for the farthest solar-powered object ever launched.