Four Planets and a Moon
Last updated 11/9/2023 at 2:46pm
This week, the moon illuminates our evening sky as it drifts in its monthly orbit around the Earth, and it will be accompanied by the four outer planets of our Solar system.
On Oct. 23, look for the moon to lie just to the southwest of the bright planet Saturn. Of course, it doesn't really lie next to Saturn; that's just an optical illusion caused by the two appearing roughly along our same line of sight. On that night, the moon will lie about 225,500 miles from us, while Saturn will lie more than 857 million miles away – some 3,800 times farther.
Five nights later, on Oct. 28, the moon will be in its full phase – aka the "hunter's" moon – and will appear quite close in the sky to the brilliant planet Jupiter. Jupiter lies 370 million miles from us, or some 1,624 times farther than the moon on that night, so there's no danger of a collision!
Those in Europe, Africa and the Eastern Hemisphere will see a small partial eclipse of the moon that night, but we in North America will not.
What we will see is a full moon along with Jupiter and Saturn, two of the brightest objects there, but not the only planets. Also there right now are the planets Uranus and Neptune.
Neptune and Uranus will also be visited by the moon. On Oct. 25, the waning gibbous moon will lie just below Neptune, and four nights later it will pass by the planet Uranus. Unfortunately, these distant worlds are much too faint to see with the unaided eye, but a small telescope can show them if you know exactly where to aim it.
These four outer planets are quite different from the inner planets (Mercury, Venus, Mars and Earth).
First, they are what astronomers call gas giants, with no surfaces on which to stand. Unlike the inner (rocky) planets, they are made of gases that are held together by gravitation. A spacecraft trying to land on any of these worlds would just sink deeper into their clouds until it becomes crushed by the weight of the planet's atmosphere.
Second, these are significantly larger than any of the inner planets. Jupiter is the largest, some 11 times the diameter of the Earth, while Saturn is about 9 1/2 times larger. Uranus and Neptune are each about four times larger than Earth.
Finally, each is surrounded by its own ring system and dozens of moons. The rings of Saturn are bright enough to see with a small telescope, but those of the other three are not. And as of June 2023, the outer worlds are home to at least 282 moons that we know of, while the inner planets have a total of only three (Earth with one and Mars with two).
Not much else appears in the moonlight this week, so now would be a great time to check out Jupiter and Saturn with a small telescope. Uranus and Neptune are a bit more challenging to locate, of course, but if you go online to get a finder chart for each and have some patience, you might have some luck!
Visit Dennis Mammana at dennismammana.com.