Go Out: Look Up!
A Guide to the Sky, Telescopes, and Telescope Programs
Go Out: Look Up!A Guide to the Sky, Telescopes, and Telescope Programs
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| Go Out: Look Up!A Guide to the Sky, Telescopes, and Telescope Programs
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A Conjunction in Astronomy is when two objects come close to each other.
There is something implied here: one or more of them are moving relative to each other.
Most of the sky is fixed: no relative motion. Polaris and Sirius, fixed, will never have a conjunction.
Something's gotta move.
Naked eye objects that move are the Sun, the Moon, Mercury, Venus, Mars, Jupiter and Saturn. Occasionally, you can see a naked eye comet or asteroid.
All of the above move across the background of a fixed celestial star field. Fairly regularly, the Moon or a planet will get close to a bright star.
Less regularly the moon will pass near a planet or a planet will pass by another planet.
Because the orbits of the moon and planets are inclined to some degree to each other, they don't always pass close by. Some passes are closer than others.
When the two best telescopic planets, Jupiter and Saturn, pass each other, it's called a Great Conjunction. They occur every 19.6 years. The last one was in 2000 and was too close to the sun to see well (see Wikipedia: Great Conjunctions).
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On December 21 of this terrible year, we are gifted with a great Great Conjunction: Jupiter and Saturn - amazing binocular and telescope targets on their own: will pass very close to each other. Close enough to be seen together in binoculars or telescopes at low to medium magnification. The moon is half a degree in diameter; Jupiter and Saturn will pass within 0.1 degree! The image to the right is to scale and shows what you would see in binoculars or a telescope near the closest pass (the image doesn't show Saturn's rings, which you can see even in small binoculars, and other than Titan, Saturn's moons are very faint). Some are calling this The Best Conjunction Ever. Expect thousands of photos the next day. This is a planetary astrophotographer's dream shot.
More info here: https://earthsky.org/astronomy-essentials/great-jupiter-saturn-conjunction-dec-21-2020 |
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Tonight after sunset, go outside and look South.
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The brightest "star" is Jupiter. To the upper left of it is a dimmer "star" with an orangish hue. That is Saturn. It's brighter than anything else in the area. Binoculars and telescopes will resolve Jupiter and its moons discovered by Gallileo and Saturn, its rings and Titan (the largest moon in the solar system (we have a probe sitting dead in the mud there)). If you go out every night and look at them, you'll find them slowly and consistently moving west. If you look at anything in the sky (other than the Moon), you'll see everything moving to the west at one degree per day. This is because the Earth is moving to the east in its orbit at one degree per day. Interesting coincidence? No. The reason we have 360 degrees in a circle is because we going around the sun in 365.25 days. A degree is essentially the drift per day. In addition to the earth-caused drift of the planets, Jupiter and Saturn are moving east around the sun, Jupiter faster than Saturn. Over the days to Dec. 21, you see Jupiter outpacing Saturn in the race east, closing the gap between them.
Don't wait until December. Practice photographing early, it's a little tricky getting things right... |
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| Draw a line from the Moon to Jupiter. Extend it a bit, there's Saturn. Extend the line quite a bit, and you'll intersect bright orange Mars. That's your ecliptic (more or less). Jupiter, Saturn, and Mars will slide down it past the sun to emerge in the morning sky. |
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Questions or comments? Email:Jeff Martin
Questions or comments? Email:Jeff Martin
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Questions or comments? Email:Jeff Martin |