The Great Conjunction of 2020

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!

Hubble’s latest portrait of the “Lord of the Rings”

NASA’s Hubble Space Telescope captured this image of Saturn on July 4, 2020. Two of Saturn’s icy moons are clearly visible in this exposure: Mimas at right, and Enceladus at bottom. This image is taken as part of the Outer Planets Atmospheres Legacy (OPAL) project. OPAL is helping scientists understand the atmospheric dynamics and evolution of our solar system’s gas giant planets. In Saturn’s case, astronomers continue tracking shifting weather patterns and storms. Credits: NASA, ESA, A. Simon (Goddard Space Flight Center), M.H. Wong (University of California, Berkeley), and the OPAL Team

Saturn is truly the lord of the rings in this latest portrait from NASA’s Hubble Space Telescope, captured on July 4, 2020, when the opulent giant world was 839 million miles from Earth. This new Saturn image was taken during summer in the planet’s northern hemisphere.

Hubble found a number of small atmospheric storms. These are transient features that appear to come and go with each yearly Hubble observation. The banding in the northern hemisphere remains pronounced as seen in Hubble’s 2019 observations, with several bands slightly changing color from year to year. The ringed planet’s atmosphere is mostly hydrogen and helium with traces of ammonia, methane, water vapor, and hydrocarbons that give it a yellowish-brown color.

Hubble photographed a slight reddish haze over the northern hemisphere in this color composite. This may be due to heating from increased sunlight, which could either change the atmospheric circulation or perhaps remove ices from aerosols in the atmosphere. Another theory is that the increased sunlight in the summer months is changing the amounts of photochemical haze produced. “It’s amazing that even over a few years, we’re seeing seasonal changes on Saturn,” said lead investigator Amy Simon of NASA’s Goddard Space Flight Center in Greenbelt, Maryland. Conversely, the just-now-visible south pole has a blue hue, reflecting changes in Saturn’s winter hemisphere.

Hubble’s sharp view resolves the finely etched concentric ring structure. The rings are mostly made of pieces of ice, with sizes ranging from tiny grains to giant boulders. Just how and when the rings formed remains one of our solar system’s biggest mysteries. Conventional wisdom is that they are as old as the planet, over 4 billion years. But because the rings are so bright – like freshly fallen snow – a competing theory is that they may have formed during the age of the dinosaurs. Many astronomers agree that there is no satisfactory theory that explains how rings could have formed within just the past few hundred million years. “However, NASA’s Cassini spacecraft measurements of tiny grains raining into Saturn’s atmosphere suggest the rings can only last for 300 million more years, which is one of the arguments for a young age of the ring system,” said team member Michael Wong of the University of California, Berkeley.

Two of Saturn’s icy moons are clearly visible in this exposure: Mimas at right, and Enceladus at bottom.

This image is taken as part of the Outer Planets Atmospheres Legacy (OPAL) project. OPAL is helping scientists understand the atmospheric dynamics and evolution of our solar system’s gas giant planets. In Saturn’s case, astronomers continue tracking shifting weather patterns and storms.

Eclipse, not — Conjunction, hot!

See the eclipse? Not sure we can either. Side-by-side images made about half an hour apart, shot and processed with identical settings.

Penumbral lunar eclipses — when the Moon passes through the thin outer shadow Earth casts into space — are not spectacular. We described the July 4 – 5, 2020 eclipse as “subtle” when we wrote about it in advance. It turned out to be not-even-subtle. Essentially nobody could tell whether an eclipse had even happened, even in photographs tortured to bring out shadow details. Announcing penumbral eclipses is tricky: if nothing is said about them before they happen, we get asked why; if we promote the eclipse and even say it may be slight, people get disappointed when they hardly see the effects or don’t see anything happen at all. Still, we got to talk about the geometry of eclipses and people looked at our beautiful Moon, and that’s something.

A gorgeous high resolution portrait of Earth’s Moon at the height of the penumbral eclipse of July 4 – 5, 2020. Can’t see the eclipse shadow? Nope. That’s okay with the photographer. Credit: Alan Studt.

CAA member and accomplished photographer Alan Studt took advantage of the brilliant Moon to make its portrait. Studt explained this photo of the Moon is a composite, made up of images recorded at the peak of the eclipse. “Never saw a shadow,” he wrote, “which was fine with me.”

The Moon was shot with a telescope focal length of 4,400mm, at f/20, 1/80th sec., and ISO 250. It is made of 12 images (4 rows of 3 images)
stitched together in Lightroom and post-processed using Camera RAW in Photoshop.
Happily for skywatchers, the July Fourth holiday weekend presented a second opportunity for enjoyment: the conjunction of the “Full Buck Moon,” with planets Jupiter and Saturn. Clouds interfered, or possibly enhanced, photographic efforts. By eye, the trio was glorious with the dominant Moon, brilliant Jupiter, and shy Saturn gracing a sky full of moonglow.

Shot about an hour after moonrise, the Full Moon glowed brilliantly orange, lending color to the encroaching clouds. Jupiter is above Moon in this photo, Saturn is at the edge of a cloud on the left. A single DSLR exposure. Photo by James Guilford.

Alan Studt made his picture from two different shots/exposures: One shot for the clouds & one shot for the Moon. The clouds, Saturn, Jupiter and its moons (look closely at Jupiter) were all in one shot, 180mm, f/5. Just the Moon & clouds shot were 550mm, f6.3 Sky: 1/13th sec., ISO 5000. Moon: 1/125th sec., ISO 80. The images were post-processed in Lightroom & layer blended in Photoshop.

Conjunction photo combines separate exposures to show lunar features as well as moonlit clouds. Look closely, you may be able to make out the tiny dots of the Galilean Moons. Photo by Alan Studt.

Matt Franduto

Conjunction. by Matt Franduto.

Final Public Stargaze: October 5

Graphic: International Observe the Moon Night - October 5, 2019
Save the Night: International Observe the Moon Night, October 5, 2019

The year’s final public stargazing session hosted by the Cuyahoga Astronomical Association (CAA) will take place Saturday, October 5, from 8:00 to 10 p.m. at our Letha House Park West observatory site.

Given good sky conditions visitors will be able to view Jupiter, Saturn, star clusters, and Earth’s Moon. In fact, the date coincides with International Observe the Moon Night: a worldwide appreciation of our world’s nearest neighbor in space.

The event is free, open to the public, and is conducted as an “open house” — visitors may arrive and depart at any time during the event’s hours. The CAA’s observatory will be open and association members also will be on hand to share views through their personal telescopes.

An interesting activity any time of year is to make note of the daily changes we see in the phases of Moon. Open the PDF to print a handy guide and journal for lunar observation: Moon Observation Journal.

To find our observatory, and what to expect with a “star party,” visit the following: https://cuyastro.org/caa-observatory/