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Find the Ecliptic After Dark


Last updated 2/15/2024 at 10:55am

It is roughly along the arc of the ecliptic that we will always find the sun, moon and planets, and this week we can spot several just after dark.

This week we can see something that many beginning sky watchers miss. I say we can "see" it, but in reality, it's invisible except in our imaginations. I'm referring to what astronomers know as the "ecliptic."

The ecliptic outlines the path that the sun, moon and planets of our Solar system take as they wander our skies from night to night and from month to month.

The planets orbit our sun, and the moon orbits the Earth, all in nearly circular paths that lie roughly on the same geometric plane. We on Earth, of course, lie on the inside of this Solar system, so when we gaze outward, we see these bodies along an arc that spans the sky.

It's along this arc that the planets, sun and moon appear to move over time. We call it the ecliptic because, as you might imagine, this is the only place where eclipses can occur.

The ancients may not have known its true nature, but they certainly noticed the pattern, and they created a set of constellations through which these Solar system bodies appeared to wander over time: the zodiac. This week after sunset we can see Sagittarius, Capricornus, Aquarius, Pisces, Aries and Taurus along the ecliptic in our southern sky.

It is roughly along this arc that we will always find the sun, moon and planets, and this week we can spot several just after dark. Some are pretty easy to find, but others are a bit tougher.

First off, look for the full moon low in the east after sunset on Nov. 26. Not far to its west on that night lies the brilliant planet Jupiter. Even without the moon to guide us, it'll be hard to miss this stunningly bright object. Appearing farther to the west, and much fainter than Jupiter, lies Saturn.

By connecting the moon, Jupiter and Saturn with an imaginary line and extending it completely across the southern sky you can trace the ecliptic. Along the way you will have encountered three other planets, though they're quite a bit more challenging to find.

The easiest of these is Mercury. I say it's easiest only because it's visible to the unaided eye, but it lies very low in the southwestern sky for only a short time during dusk. You will need a clear sky and low horizon toward the southwest – and possibly even binoculars – to spot this elusive planet.

If you have a small telescope, you'll be able to find the other two planets there right now. Uranus is the easier of the two; now lying its closest to Earth it will appear in a small scope as a tiny bluish-green dot. Those with excellent eyesight might even spot it with the unaided eye, but only from a dark location with no moonlight to interfere.

Neptune... well, here's a real challenge. Only if you know where to aim a small telescope will you see Neptune as a tinier and fainter version of Uranus.

It's only along this ecliptic band that we will ever find the sun, moon and planets. If ever they should appear elsewhere... well, you'll know something has gone terribly wrong!

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