Jupiter-Saturn Great Conjunction: Watch Best View Since Middle Ages!

by Lance D. Davis

Stargazers get ready for a nice treat as we are about to witness a super-rare planetary alignment not seen for almost 800 years!

Our solar system’s two biggest worlds – the mighty Jupiter followed by the glorious ringed Saturn – will appear in the sky next to each other at their closest since 1623 and closest visible from Earth since the Middle Ages in 1226. This will happen on Dec. 21, 2020, during an event called a “great conjunction.”

Astronomers use the word conjunction to describe close approaches of planets and other objects on our sky’s dome. They use great conjunction specifically for Jupiter and Saturn because of the planets’ top-ranking sizes.

view of the 2020 great conjunction through the naked eye just after sunset
A graphic made from a simulation program, showing a view of the 2020 great conjunction through the naked eye just after sunset at approximately 5:15 p.m. (EST) on Dec. 21.
Credit: NASA

Great conjunctions between Jupiter and Saturn happen every 20 years, making the planets appear to be close to one another. This closeness occurs because Jupiter orbits the Sun every 12 years, while Saturn’s orbit takes 30 years, causing Jupiter to catch up to Saturn every couple of decades as viewed from Earth.

The last conjuction between these planets took place on May 28, 2000. This year’s conjunction occurs on Dec. 21, which coincidentally is also the date of the winter solstice in the Northern Hemisphere. The 2020 conjunction is unique because of how close Jupiter and Saturn will appear. In most conjunctions, Jupiter and Saturn pass within a degree of each other. This year, they will pass 10 times closer to each other – the closest in nearly 400 years.

view of the 2020 great conjunction through a telescope
A graphic made from a simulation program, showing the view of the 2020 great conjunction
through a telescope at approximately 5:15 p.m. (EST) on Dec. 21. Credit: NASA

Currently, you can watch Jupiter and Saturn get closer in Earth’s sky each evening until their grand finale on Dec. 21. Just look for them shortly after sunset, shining brightly and low in the southwestern sky. Also, tune in to NASA Science Live or NASA Facebook on Dec. 17 at 3:00 p.m. EST (2:00 p.m. CST) and learn how to see Jupiter and Saturn’s great conjunction.

During the great conjunction, the giant planets will appear just a tenth of a degree apart – that’s about the thickness of a dime held at arm’s length! This means the two planets and their moons will be visible in the same field of view through a small telescope. Truly, this is a once-in-a-lifetime event!

Some astronomers suggest the pair will look like an elongated star and others say the two planets will form a double planet. To know for sure, we’ll just have to look and see. Either way, take advantage of this opportunity because Jupiter and Saturn won’t appear this close in the sky until 2080!

Additional Information & Resources:

Learn how to photograph the Jupiter-Saturn conjunction.
Read about mission visits to Jupiter and Saturn.
Find an astronomy club or event near you!

Total Solar Eclipse to Cast Shadow on South America

by Lauren Lambert

What is a Solar Eclipse?

A solar eclipse is a natural phenomenon that occurs when the Moon passes between the Sun and Earth. This event happens when the Moon completely blocks the Sun and the Moon’s shadow falls onto a portion of the Earth’s surface.

There are three types of solar eclipses: total, partial and annular. During a total solar eclipse, observers can witness daytime twilight because the disk of the Moon blocks 100% of the Sun. During a partial solar eclipse, the Moon is not entirely covering the Sun and you will likely not notice any difference in light intensity. You may only notice a subtle difference if the partial eclipse is close to total and you go outside at maximum eclipse.  Lastly, an annular eclipse can be observed when the Moon is at apogee, or the farthest from Earth within its elliptical orbit. This causes a ring of light, or annulus, to be visible around the Moon, which is sometimes referred to as the “ring of fire.”

total solar eclipse image
During the total solar eclipse, the Sun’s visible-light corona (meaning crown), only visible at maximum eclipse from within the path of totality, is seen here as a crown of white light extending from around the edge of the eclipsing Moon. The red loops of material also seen around the edge, are called prominences, in which magnetic fields enclose hot solar material. Credit: NASA/Armstrong’s Gulfstream III.

Total eclipses are of particular interest to solar scientists, because with the Moon blocking the bright light of the Sun, you can see the Sun’s atmosphere from the ground.  Solar scientists at Marshall Space Flight Center, and around NASA, make use of telescopes called coronagraphs that block the Sun so they can see the dim atmosphere, the corona, around it. But — given how perfectly the Moon lines up with the Sun — you can see the atmosphere closer to the surface of the Sun than we even can with our telescopes in space.

The shadow of the Moon on a planet during an eclipse can be described using three terms: umbra, antumbra and penumbra. The umbra is the shadow that is cast when the Moon completely covers the Sun and is where the path of totality falls. If the Moon is further away from the Earth, it is unable to block the Sun entirely. The Sun appears as a ring of light around the Moon. In this case, the shadow is known as the antumbra, or path of annularity, and occurs during an annular eclipse. Similarly, a partial solar eclipse can be observed when only a portion of the Moon blocks the Sun and creates a shadow referred to as the penumbra. The penumbra also occurs surrounding the umbra during a total eclipse, effectively covering those regions on the planet that only have a view of a partial eclipse.

Crescents of light from solar eclipse
Crescents of light are projected onto the ground during the partial phases of a solar eclipse due to light from the Sun passing through gaps between the leaves of trees, a pinhole effect. This is a safe and indirect way to view a solar eclipse. Credit: NASA/Johnson Space Center

Solar eclipses happen at least twice per calendar year, with total solar eclipses occurring about once every year and a half. But the possibility of seeing them is rare if you’re not in the right place at the right time. Additionally, since Earth is made up of mostly water, the path of totality, or the area receiving total blockage of the Sun, may not necessarily fall on land.

The year of 2020 sees two solar eclipses. The first occurred on June 21 and was an annular solar eclipse, visible from the continents of Africa and Asia. The second will be a total solar eclipse, occurring on Dec. 14, visible from South America. The path of totality crosses over Chile and Argentina, but some of their areas outside of the path of totality will experience a partial solar eclipse. The total eclipse will also be visible in Antarctica, South Africa, as well as the Pacific, Atlantic, and Indian Oceans. Observers will be able to witness the total solar eclipse for about 2 minutes.

If you are not within the path of totality, watching the total solar eclipse from a virtual location is an option as well. You can view it on NASA TV and the agency’s website, beginning at 10:30 a.m. EST on Dec. 14.  Be sure to check it out, as the next total solar eclipse won’t be happening until Dec. 4, 2021.

Top 5 Solar Eclipse Viewing Tips:

  1. Do not stare directly at the Sun. Wear safety approved, protective solar eclipse-viewing glasses to directly view the event or use some indirect means (see below). For more information here are some NASA Safety tips.
  2. To indirectly view the eclipse, create a pinhole camera or box projector. Learn how to build your own here.
  3. Stand under a tree and look at the ground. The trees act as pinhole projectors and will project hundreds of crescent shapes right at your feet.
  4. To capture an eclipse with binoculars, a telescope, or a camera, you must use a safety-approved, protective solar filter on your lens.
  5. Keeping with the theme of 2020 Observe the eclipse virtually! It will be streamed live here.