Al Stahler: Jupiter, Saturn and moon
Jupiter orbits half-a-billion miles out from the sun … Saturn, nearly twice that. There is no risk of these planets colliding … or even coming remotely close to each other.
That won’t keep Jupiter and Saturn from appearing to be close together – very close – when we look up at them in the sky.
Jupiter and Saturn will be easy to find in the Thursday or Friday night sky, and once you see them, they’ll be easy to find next Monday, when they reach their grand conjunction – their close approach in the sky.
Take a look around your room. Pick out something nearby – I’m using a floor lamp, near my chair.
Now look at something, in the same direction, a bit farther away – I’m looking at a table, almost behind the lamp. Ignoring distance, lamp and table seem to be side-by-side.
Now … moving my head one way or the other, I can make lamp and table appear to move sideways … to move away from each other … or to move closer.
Looking out, into the sky tonight, Saturn is almost, though not quite, behind Jupiter (half-a-billion miles behind).
Our head, firmly attached, follows our body everywhere. And our body, held down by gravity, follows the Earth wherever it goes. As Earth moves around the sun, it takes our bodies – and our heads – with it.
Looking at the sky, from one night to the next, Earth moves our head, one way or another. Like the table that seems to move toward the lamp, Saturn seems to be moving toward Jupiter.
National Weather Service forecasts tonight’s sky to be mostly clear, which will make it easy to find the moon.
After last Monday’s (invisible) new moon, the moon is now a crescent, easy to find in the southwest as soon as the sky grows dark.
To the right of the crescent moon – brighter than any star – is Jupiter. Jupiter is huge – if it could be weighed, it would tip the balance at more than three hundred Earths. Immense mass gives Jupiter an immense gravitational field – powerful enough to tweak our own planet’s orbit, contributing to the forces that push Earth into (and, mercifully, pull us out of) ice ages.
Huge size also allows Jupiter to reflect lots of sunlight, which is why it’s so bright.
And off the giant planet’s shoulder – at about ten o’clock – is planet Saturn. Farther from the sun, Saturn receives less sunlight than Jupiter. Farther from Earth, less of Saturn’s reflected sunlight reaches our eyes. Saturn is not nearly as bright as Jupiter … but it is visible.
Both Jupiter and Saturn have dozens of moons. Several of Jupiter’s four largest (and brightest) moons are often visible in binoculars – just be sure to brace your elbows on something solid – a table, a railing – to keep the binocs steady.
As Earth carries our bodies, our heads, our eyes around the sun, Jupiter and Saturn will appear to move closer and closer, reaching their grand conjunction next Monday.
Al Stahler enjoys sharing science and nature with friends and neighbors in The Union and on KVMR-FM. He teaches classes for both kids and grown-ups, and can be reached at email@example.com.
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