The first half of this year, a single planet caught everyone’s eye. Well, not everyone, just those who were up before dawn. That’s when riveting Venus lit up the eastern sky. But where were all the other planets?
They were bunched up on one side of the Sun, and only now have all emerged in their full glory. Even though Mars has currently gotten very bright at it readies itself for its close approach on December 8, it’s not out until after midnight. And Saturn, while bright but not brilliant, doesn’t catch anyone’s attention unless it’s pointed out. Which the Moon will accomplish on October 5, when it hovers just below Saturn, making that ringed world a cinch to find.
But we’ll focus on two others — Jupiter in Pisces and Neptune in Aquarius. Jupiter because it’s the very brightest “star” in the whole sky, and automatically catches everyone’s attention all night long. It arrived at its closest of the year, and brightest and biggest on September 26, so it’s at its best right now. On top of that, we are meeting Jupiter at the narrowest gap between the orbits of it and Earth, meaning it’s as bright as it ever gets! Astronomers measure it at magnitude -2.9, which is three times more brilliant than the night’s brightest true star, Sirius. You can catch its creamy brilliance any night, or you can see it hovering near the Moon on October 8.
Another distant planet has also reached its closest point to Earth — Neptune. Normally we ignore that most distant planet because it’s the only one that cannot be glimpsed with the unaided eye. It’s also the only one not originally found by an observer inspecting the night sky. Rather, that blue ball, big enough to let 58 planet Earths fit inside if it were hollow, had a unique discovery history, a story we’ll tell in a moment. It’s been in the public spotlight lately because the James Webb telescope recently published a cool infra-red photo of it that nicely shows its skimpy rings, which normally cannot be seen at all.
As it circles the sun every 165 years, Neptune spends about 13 years in each zodiac constellation, and it’s just beginning its time in dim Aquarius. But even with a good backyard telescope, it appears as a faint, tiny, blue disk that appears the same size as a quarter-dollar coin located 1 ½ miles away. We’re talking small. Yet it first grabbed the world’s headlines back on September 23, 1846 when it was found by an astronomer using the nine-inch telescope at the Berlin observatory. He never got credited for Neptune’s discovery because that accomplishment belonged mainly to the French astronomer Urbain Le Verrier, who realized that Uranus was moving a bit oddly and that something must be tugging at it gravitationally. In 1845 he calculated where the mysterious object should be located and, the next year, tried to get astronomers to aim their telescopes there. No one in France was interested, but Le Verrier finally convinced the Berlin observatory to take a look, and in just one hour they found Neptune within a single degree of the predicted spot.
My favorite Neptune fact is that it’s gravitationally locked into a 2:3 orbital resonance with the demoted ex-planet Pluto. This means that just as Pluto makes two trips around the Sun, Neptune makes exactly three.
Neptune has 14 Moons, with a single huge one named Triton, which is the solar system’s only major satellite that orbits in the wrong direction, namely clockwise if you’re looking at it while north of the planet. Moreover, two of Neptune’s tiny Moons orbit that blue world in a highly squashed ellipse that takes them 30 million miles away from Neptune. That’s an impossibly large distance for a Moon to be. It’s farther from Neptune than Venus is from Earth. So screwy things are happening there.
But if you want even more, well, Neptune’s winds blow five times faster than tornadoes — the fastest winds yet detected anywhere in the known universe. It’s also the coldest planet, and, moreover, is made of gases that turn slushy and liquidy further down so that there’s no solid surface to land on. Bottom line — Neptune is one of those “look but don’t touch” places where no human will ever go. So rings or no rings, we’ll talk about its oddities once a decade or so, but spend our time observing other things. Like magnificent Saturn and Jupiter, floating above the Moon on October 5 and 8, respectively.