conjunction

The Great Conjunction of 2020

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On December 21, 2020 Jupiter and Saturn will appear closer in our sky than they have since the year 1623 — only .10º apart. By way of comparison, Earth’s Moon covers about .50º on average! In fact, the two planets will have so little visual separation that they may appear as one bright “star” in our evening sky. As with many objects we see in our night sky, planets Jupiter and Saturn will only appear to be near to each other; they will will be physically separated by about 456 million miles.

The position of the planets as they will be at 7:00 PM EST, December 21, 2020. The bright green line represents the sight line from Earth to Jupiter and Saturn. Image Credit: SkySafari / James Guilford

Here’s why the planets will appear so close in our sky:

Viewed from Earth and looking out toward Jupiter and Saturn we see the planets as if they were in the same orbit — like watching runners in their separate lanes as one overtakes the other. Viewed from “above” we can see that the planets remain well apart.

Viewed closer to the orbital plane of the planets we see how Jupiter and Saturn appear closer together against the background of space. The green line represents the sight line from Earth to the planets. Image Credit: SkySafari / James Guilford

As we drop lower and closer to the orbital plane it becomes more difficult to separate Jupiter and Saturn until, on December 21, 2020, we won’t be able to see them as discrete objects without the use of a telescope!

Jupiter and Saturn appear to merge, on December 21, 2020 as viewed from Earth and depicted here just above the orbital plane of the planets. Image Credit: SkySafari / James Guilford

While the previous extremely close conjunction took place in 1623, Jupiter and Saturn were too close to the Sun to be observed. The last time they could actually be seen so close together was even longer ago: on March 4, 1226. Great Conjunctions take place just short of 20 years apart and most are not so close as this year’s — the next will take place on October 31, 2040, when Jupiter and Saturn will be separated by 1.1º which will be close, but not so amazing as 2020.

Jupiter and Saturn may be seen in the same narrow field of view during 2020’s Great Conjunction. This simulation depicts the position of Jupiter’s Galilean Moons and Saturn’s giant satellite, Titan. Image Credit: SkySafari

If you plan to take a look, you’ll need clear skies (of course!) and you’ll need to be timely — the planetary pair will become visible low in the southwestern sky with the fading twilight and will set in the west by 7:20 PM, December 21. To see the individual planets during their close encounter will require a telescope — a small one will do — or a decent telephoto lens on a camera mounted on a tripod. Given good optics and clear skies, viewers will be able to make out the Galilean Moons of Jupiter and, perhaps spy Titan, Saturn’s brightest moon.

Before and after the 21st, Jupiter and Saturn will appear close together as they first approach, and then recede from the conjunction, continuing to move along their orbital paths. The historic astronomical event will be one night and one night only in our lifetimes. Clear skies, please!

Moon and Mars Pair Up Night of October 2

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Earth’s Moon and Planet Mars will be just over one degree apart at 12:18 AM EDT, Saturday, October 3, as viewed from the Hiram, Ohio area. Credit: Sky Safari/James Guilford

The night of October 2 – 3 will see a brilliant pairing of lights, a conjunction, in our night sky. Earth’s Moon and planet Mars will shine close together — only a smidgen over a degree apart — in the southeast. As viewed from the Hiram, Ohio area, Moon and Mars will be nearest each other at 12:18 AM EDT. Don’t worry if you can’t stay up, the two will be a beautiful pair to behold all night long.

Our Moon will be a day past Full and in its Waning Gibbous phase, so it will be round and bright. Mars, while too distant to be seen as a disc by the unaided eye, is nearing an unusually close approach to Earth during its opposition and will shine like a coppery star. Mars will be nearest to Earth, at 62 million kilometers (38,525,014 miles) distant, on October 6 and it won’t be that close again until 2035.

Opposition refers to a time in their orbits when Mars (or another planet) is opposite the Earth from the Sun — around that time is when the two bodies, on concentric racetrack orbits around the Sun, pass each other and are at their closest and brightest.

July Fourth weekend brought sky events great and small

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Little difference can be seen between an earlier stage and the maximum eclipse state of the July 4 - 5, 2020 penumbral lunar eclipse. Photos by James Guilford.
Little difference can be seen between an earlier stage and the maximum eclipse state of the July 4 – 5, 2020 penumbral lunar eclipse. The images were made with identical camera and Photoshop settings. Photos by James Guilford.

There was much ballyhoo surrounding the penumbral lunar eclipse that would take place the night of July 4 – 5, 2020. We joined in just to explain a little about what was going on and what might be expected. Penumbral lunar eclipses take place when the Moon passes through the thin outer shadow Earth casts out into space; they are often very subtle, slight, and in this case, nearly undetectable. Just witness the photo above that shows the Full Buck Moon about one-half hour before maximum eclipse and the Moon at maximum. Casual observers saw no change across the entire event and it’s hard for us to see the difference even in photos that can be made to emphasize features! So we apologize if you waited up to see what we called the  “subtle” eclipse but, if you did, you saw a beautiful Full Moon!

Then there was the much-less-promoted Sunday night, July 5, conjunction of Earth’s Moon, with planets Jupiter and Saturn… a lovely sight! We went out to photograph it an hour after moonrise and spied a brilliant orange Moon lighting up the scattered clouds with Jupiter shining through and Saturn making a somewhat dimmer appearance. A conjunction is when two or more celestial objects appear close together in our skies — emphasis on appear since Moon, Jupiter, and Saturn are separated by hundreds of millions of miles. We were surprised to see, in the photo below, that even Jupiter’s four Galilean Moons can be seen. The stars and planets appear oblong or as short streaks due to Earth’s rotation and the length of the camera exposure.

Conjunction of Earth's Moon, with planets Jupiter (bright dot above), and Saturn (less bright dot to the left at the edge of a cloud), the night of July 5, 2020. Photo by James Guilford.
Conjunction of Earth’s Moon, with planets Jupiter (bright dot above), and Saturn (less bright dot to the left at the edge of a cloud), the night of July 5, 2020. Photo by James Guilford.

Jupiter and Venus converge June 30

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Image: Jupiter and Venus Converge June 30 - Chart Courtesy Sky & Telescope
Jupiter and Venus Converge June 30 – Chart Courtesy Sky & Telescope

Let’s hope for clear skies the evening of June 30 when the ongoing conjunction of Jupiter and Venus gets really cozy! Tuesday evening will see the two planets sharing a space only 1/3-degree apart in our sky; they will look like a brilliant double star. After Tuesday’s encounter, the planets will drift slowly apart night-by-night but will remain a beautiful sight in twilight. Chart courtesy Sky & Telescope – SkyAndTelescope.com