Jupiter’s oppositions occur a month later each year, because each time our planet catches up to it in space, it has moved on a bit in its 12-year orbit. Since its path is elliptical, we sometimes meet it at a narrower and sometimes at a wider point. This year is as narrow as it can possibly get. It’s now at its very closest to us since this century began. It won’t come this close again until the year 2026.
When it’s this close, it of course looks very big, attaining some 50 arc-seconds of size in our sky. That’s easily large enough to show a disk through plain binoculars. Viewed with even the smallest telescopes, Jupiter offers a worthwhile target. Its four planet-class satellites become instantly obvious – though one of them, usually Io, often darts invisibly in front of or behind the planet. The moons always appear in a straight line, since they encircle Jupiter’s Equator, which in turn moves through space horizontally: Jupiter travels with just a negligible three-degree tilt to its axis.
Making things even better for observers, Jupiter has been steadily climbing northward during its dozen-year creep along the Zodiac, so that this year, in Aries, it gets high up around midnight. That’s important in keeping its image above the thickest, blurriest parts of our atmosphere, and grants telescopic observers a steadier image.
Alas, from this part of the country the air is almost in a state of blurriness, characterized to the naked eye by twinkling stars. So if you do have a telescope, first check out whether the stars are dancing or calm before dragging it out to aim it toward the giant planet. Only on rare, steady nights and with good equipment will you glimpse the white ovals, red spot (which has actually been orange the past two years) and wonderful curlicues and festoons for which the giant planet is famous.
Here’s something cool: Go to slooh.com and enjoy the free live Jupiter Internet show that I’ll offer on Saturday night (the 29th) from 7 to 9 p.m. We’ll use Slooh’s large telescopes in the Canary Islands to show you Jupiter in all its glory, accompanied by real-time narration. Mark it on your calendar.
But if all you care to use is the naked eye, fine. Look around tonight – or anytime the next couple of months – for the sky’s brightest star, and just salute this closest approach of the largest planet.