Advising readers to scan the night sky this time of year always feels a little awkward, because the Pacific Northwest’s view-obscuring cloud cover is legendary in winter. (Not to mention fall and spring.) You never do know if all the bright, shiny stuff up there will be wrapped in a wet, dark blanket.
If we do get lucky with clear night skies this month, looking up will be worth it.
You may have already noticed one standout shiny star that’s been rising after sunset and crossing the night sky in recent months. This weekend, that shiny star will reach maximum visibility and brilliance, from our point of view.
Jupiter is our solar system’s planetary supergiant. With a diameter of 88,000 miles, Jupiter is 11 times larger than Earth. Its volume is over 1,300 times the Earth’s — that is, more than 1,300 Earths could fit inside of Jupiter. Jupiter’s gravity is so immense, science fiction writer Arthur C. Clarke theorized in his novel “2010: Odyssey Two” that Jupiter’s super-compressed heart could be the largest gem in the universe.
“There, by one of Nature’s supreme jests, was something very precious to mankind,” Clarke writes. “The core of Jupiter, forever beyond human reach, was a diamond as big as the Earth.”
In coming days, supergiant Jupiter will achieve two orbital milestones: opposition and perigee.
Opposition simply means that an outer planet is directly opposite the sun, with Earth in between. It’s as if the sun and Jupiter sit at two ends of a cosmically long string, with Earth perched somewhere along that straight line. When the sun sets, Jupiter rises (in the east-northeast, just before 4:30 p.m. Saturday). When the sun rises the next morning, Jupiter sets.
A planet in opposition is also in “full phase,” reflecting sunlight back at us with maximum fullness and brightness — especially at midnight, when the bright planet climbs to its highest point in the contrasting darkness.
Opposition only applies to the outer planets — the ones farther away from the sun than Earth. Inner planets Mercury and Venus are closer to the sun than we are, so they never appear on the other side of the sky.
Meanwhile, Jupiter is also drawing closer to Earth than its irregular, oval-shaped orbit has brought it since 2022. That point of planetary closeness is called perigee. On Dec. 6, the distance between Jupiter and Earth will shrink to an intimate 380 million miles, according to the website earthsky.org.
Put all these phenomena together — Jupiter’s hugeness, its full-phase brilliance and its passing proximity to Earth — and you’ve got the perfect conditions for a planet that really pops in our night sky. Jupiter can get so surprisingly brilliant on and around its opposition and perigee, the occasional unsuspecting sky spectator has been known to wonder — and worry — what that humongous, motionless, gleaming thing might be. In October 2010, according to The Peninsula Daily News, the Clallam County Sheriff’s Office fielded numerous reports of a UFO that turned out to be shimmering Jupiter.
While oppositions can be pretty spectacular, they’re not rare. They occur about once a year as Earth’s speedy orbit sends us whizzing past all the slower-moving outer planets. (It takes Jupiter 11.9 years to orbit the sun.) As we do that, those planets sometimes appear to start looping backward in the sky, in an illusion called retrograde motion.
Viewing Jupiter
Jupiter was a prime target of inventor and astronomer Galileo’s innovation, the telescope, in 1610. As he started tracking the movements of four little white dots around the planet, Galileo realized he was witnessing a cosmic proof of the law of gravitation, with satellite worlds circling a massive one.
You can make the same discovery for yourself. Get out your binoculars and train it upon the planetary giant. It’ll be hard to miss four points of light hugging the planet and moving around it, night after night. Those are the Jovian satellites Io, Ganymede, Callisto and Europa. All but the latter are larger than Earth’s moon.
Galileo was the first to discover another planet’s moons. In the years since, astronomers with better technology than hand-made telescopes have spotted many more moons around Jupiter. The count is now up to 95 moons, according to NASA.
With sufficiently powerful binoculars, you’ll also be able to make out the churning cloud bands that encircle the planet. If not, Jupiter’s sharp brilliance is still guaranteed to impress. Jupiter will remain visible in our night sky through April 2025.
What else is up?
Red planet Mars will grow distinctly bright in December as it gets ready for its own oppositional star turn Jan. 16. Mars rises in the east-northeast at about 8 p.m. Saturday, but by the end of the month it’ll be appearing hours earlier. While it’s tough to see any detail without a powerful telescope, Mars’ ruddy shine makes it unmistakable in the sky.
Finally, don’t get too excited about the peak of the annual Geminids meteor shower, expected Dec. 13. That’s because a waxing moon will also be preparing to peak (on Dec. 15), likely washing out all but the brightest shooting stars. Moonlight will last throughout that night, dampening whatever show the Geminids put on for us.
If you’re determined to catch some Geminids, the time to start looking is now, since this meteor shower is active late November through Christmas.
