GREENSBORO, N.C. — You've likely seen this headline all over the internet in the last few weeks: "Christmas Star appears on December 21, 2020". Lots of folks will look to the starry sky that Monday night because, it's true, something special will happen. Saturn and Jupiter will appear to overlap. It's called a great conjunction. The event will look like a bright star in the southwestern sky. It's also true, the event is bright and rare and, this time, it happens near Christmas.
However, it's probably not the "Christmas Star."
To better understand this, I spoke with David Weigel, the planetarium director for the INTUITIVE Planetarium at the U.S. Space and Rocket Center in Huntsville, Alabama.
How close are the planets going to be?
To be clear, Saturn and Jupiter won't literally be close to each other. Weigel said the two massive planets, each about 760 to 1,300 times the size of Earth, will still be hundreds of millions of miles apart.
The planets appear close together because of their orbits, or their paths around the Sun. Those paths aren't a perfect circle, so when both planets and the Earth reach a certain point on their paths, they appear close together from our perspective here on Earth. During this year's conjunction, Saturn and Jupiter will appear to be 0.1 degrees apart, and that's special. It will be visible in the night sky.
How often does this happen? Weigel said conjunctions happen about every 20 years. The last time this happened, in 2000, the event wasn't so impressive. Saturn and Jupiter didn't appear as close together. The last time we saw a conjunction like the one coming on December 21 was back in 1623. German astronomer Johannes Kepler had just put together his theory of celestial mechanics. Essentially, he figured out how to use math and physics to more accurately predict what the night sky looked like hundreds of years ago. Kepler was a pretty brilliant guy.
Unfortunately, the great conjunction in 1623 was a bust. Saturn and Jupiter's paths were too close to the Sun, and people likely couldn't see anything.
Before that, there was another great conjunction in 1226 AD. This one happened at night, so people likely saw it. How bright will it be?
Weigel said don't expect anything crazy. It won't be as bright as the Moon.
"It will be a treat to look at, but don't expect some enormously bright beacon in the sky," Weigel said.
Fair enough.
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- Jupiter and Saturn will appear brighter than nearly every star. They can be seen easily from large cities, and dark sites.
- Dark skies will allow you to see fainter stars, but Jupiter and Saturn are bright enough that you don’t necessarily need to go to a dark site to take compelling photos of them. If you have a clear view toward the southwest, you have the chance to take some great photos.
- Think about composition. Jupiter and Saturn will just appear as points of light. To make your photo more interesting, try to frame the planets with something – the silhouette of a tree, an outdoor landscape, the arch of a building, or even a neon sign.
- Experiment with both wide-angle and telephoto shots. In early December, the two planets will be about 2 degrees apart, and will get progressively close toward December 21. In order to show them clearly in your photos, you might use a wide-angle composition early in December, and zoom in later in the month as they get closer.
- Be sure to go outside on a few different nights, and see how their separation changes.
- Using a tripod will help you hold your camera steady while taking longer exposures. If you don’t have a tripod, brace your camera against something – a tree, a fence, or a car can all serve as a tripod for a several-second exposure.
- These planets are visible in early evening, and you'll have about 1-2 hours from when they are visible, to when they set. The color and intensity of the sky changes during that time. Stay out for an hour or more, and try to capture shots with both the bright colors of sunset, and the darkness of the oncoming night. A photo from the same location can look completely different just an hour later!
- The crescent moon will pass near Jupiter and Saturn a few days before the conjunction. Take advantage of it in your composition!
- Jupiter and Saturn will be bright enough to detect in many cell phone cameras. You won’t see additional detail by zooming in, but you can frame Jupiter and Saturn creatively.
- Some recent cell phones have a ‘night mode,’ which will automatically stabilize a long-exposure, even without using a tripod. This can be great for capturing the dark foreground of your photo. Some phones will let you use ‘night mode’ on exposures up to 30 seconds, if you also use a tripod.
- Many cell phones have a wide-angle lens. Try using this to place a subject in the foreground, with Jupiter and Saturn above them.
- At the time of conjunction on December 21, Jupiter and Saturn may be too close to separate clearly in your photos. Images taken a few days before or after the conjunction may show them more clearly.
- Set your focus to Infinity (Manual Focus mode), so the planets will be sharp. Set your aperture wide open, to let in the maximum amount of light.
- If you have a tripod, it will help you take long exposures. If not, you can still take some great pictures with a short shutter speed (< 1/4 second). If your camera or lens has an image stabilizer, be sure it is turned on.
- If your photos show that the camera is not steady, shorten your shutter speed. You can also use a photographers’ trick to get a sharp photo when hand-holding: set up your camera to take multiple exposures, then hold the shutter button to take a series of photos. While some will be blurry due to camera shake, you may find a few that are sharp.
- If you use a 200 mm telephoto lens, you should be able to see Jupiter's four bright moons in a short exposure. Saturn’s rings will usually need a longer lens or a telescope in order to resolve clearly.
- To capture Jupiter and Saturn as sharp ‘points’ while using a tripod, use a shutter speed of up to a few seconds. More than this and the Earth's rotation will smear out the planets and stars. If you are using a wide-angle lens, you can use a longer exposure.
https://solarsystem.nasa.gov/news/1615/how-to-photograph-the-conjunction-of-saturn-and-jupiter/
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- https://solarsystem.nasa.gov/solar-system/our-solar-system/overview/
- https://twitter.com/i/status/1340378052656709632
Jupiter and Saturn will appear to be so close from Earth on Dec. 21 that they may look like one shining star.
Look up at the night sky on Dec. 21 and you may see something special.
The planets of Jupiter and Saturn will appear (weather-permitting) on the winter solstice to be so close from Earth that they may look like one shining star, even though they’ll actually be 450 million miles apart.
The so-called “Great Conjunction” last happened in 1623 but could not be seen from Earth. Before that, the phenomenon previously occurred on March 4, 1226.
2020’s celestial event has been christened by some as the “Christmas Star,” due to its proximity to Christmas Day.
“Alignments between these two planets are rather rare, occurring once every 20 years or so, but this conjunction is exceptionally rare because of how close the planets will appear to one another,” said Patrick Hartigan, a professor of physics and astronomy at Rice University.
“On the evening of closest approach on Dec 21 they will look like a double planet, separated by only 1/5th the diameter of the full moon,” Hartigan explained in a statement. “For most telescope viewers, each planet and several of their largest moons will be visible in the same field of view that evening.”
“Look for them low in the southwest in the hour after sunset,” NASA recommended on its website. “And on December 21st, the two giant planets will appear just a tenth of a degree apart — that’s about the thickness of a dime held at arm’s length!”
Viewing conditions will improve the closer people are to the equator.
“The further north a viewer is, the less time they’ll have to catch a glimpse of the conjunction before the planets sink below the horizon,” said Rice. “Fortunately, the planets will be bright enough to be viewed in twi-light, which may be the best time for many U.S. viewers to observe the conjunction.”
It also depends on the weather as to how visible the conjunction will be.
Nahum Arav, a professor of physics at Virginia Tech, described the “rare event” as “special because of how bright the planets will be and how close they get to each other in the sky.”
The two planets will be “easily” seen by the naked eye, he said in a statement. “They will be very close to each other, about a fifth of the moon’s diameter. At their closest, some people will need a binocular to separate them.”
The spectacle will next reportedly occur on March 15, 2080.
After that? Well, it’s a bit of a longer wait — until the year 2400.
Check out NASA’s tips on photographing the conjunction here.
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