Astronomy EssentialsSpace

Jupiter gives us Pluto in 2020

Sky chart with line of ecliptic, Saturn, Jupiter, and arrow pointing to location of Pluto.
The year’s 3rd and final conjunction of Jupiter and Pluto will take place on November 12, 2020. The first conjunction happened on April 5, 2020, and the second one on June 30, 2020.

See the moon, Jupiter and Saturn November 18 to 20, 2020

2020 counts as a banner year for Jupiter and Pluto. That’s because giant Jupiter and tiny Pluto have a triple conjunction this year, coming together, moving apart and coming together again three times in 2020. The first conjunction took place on April 5. The second occurred on June 30, and the final one will take place on November 12. Because all of these Jupiter-Pluto conjunctions happen when these two planets are in our night sky (as opposed to being lost in the sun’s glare), this year’s close alignment of Jupiter and Pluto might be the best for centuries to come.

The 2021 lunar calendars are here! Order yours before they’re gone. Makes a great gift!

In 2020, dazzlingly bright Jupiter and extremely faint Pluto remain near each other throughout the year, snuggling up together in front of the constellation Sagittarius. Pluto requires a telescope to be seen. No telescope? Try NASA’s Night Sky Network to find star parties and/or astronomy clubs near you.

And you don’t need a telescope to use your imagination. Throughout 2020, brilliant Jupiter enables us to envision Pluto with the mind’s eye on the sky’s dome. First find Jupiter and – presto – you’ve nearly stumbled upon Pluto. Just remember, Jupiter outshines Pluto by several million times.

Where are these worlds now? In November 2020, Jupiter and Pluto light up the southwest sky at nightfall. They sink downward as evening deepens, to set around mid-evening at mid-northern latitudes, and late night in the Southern Hemisphere.

Chart: 4 positions of moon near slanted green ecliptic line and dots for Jupiter and Saturn.
Watch for the waxing crescent moon to shine close to Jupiter and Saturn for several days, centered on or around November 19, 2020. Although not shown, the dwarf planet Pluto lurks close to Jupiter on the sky’s dome. Read more.

Although Jupiter and Pluto nearly align along the same line of sight throughout 2020, these two worlds aren’t close together in space. Jupiter is a bit more than 5 astronomical units (AU) from the sun, while Pluto lodges way beyond Jupiter, in the Kuiper Belt, at over 34 AU from the sun. One astronomical unit (AU) = one sun/Earth distance.

Jupiter’s and Pluto’s present distance in AU via Heavens-Above

Here’s some observational data about Pluto for 2020, from

Visualize the solar system to scale at If the Moon Were Only 1 Pixel.

In a star field, one tiny dot jumps from one position to another.
Steven Bellavia in Mattituck, New York, captured Pluto on 2 separate nights, June 24 and June 27, 2019. In this animated gif, you can see that Pluto moved in front of the stars between those 2 nights. Steven wrote: “Most of the motion you see is actually from the Earth, not Pluto, since our motion changes our perspective of the much-closer Pluto against the backdrop of the much-farther stars.” Thanks, Steven!
Multi-colored gray, russet, and tan planet with smaller gray moon.
Mosaic image of Pluto and its largest moon Charon, captured around the time the New Horizons spacecraft swept closest to them on July 14, 2015. Image via NASA/ JHUAPL/ SwRI.

Two planets are said to be in conjunction whenever they reside north and south of one another on the sky’s dome. Conjunctions of Jupiter and Pluto recur in periods of 12 to 13 years. The previous Jupiter-Pluto conjunction happened on December 11, 2007, and the one before that on December 2, 1994. After 2020, the next Jupiter-Pluto conjunction will occur on February 4, 2033, and the one following that on April 12, 2045. But the gap between Jupiter and Pluto at each one of these conjunctions is quite far apart, and the conjunctions of 1994, 2007, and 2033 happen so close to the sun that even Jupiter is lost in the sun’s glare.

Far and away, 2020 presents the best alignment of Jupiter and Pluto in the 21st century (2001 to 2100). What’s more, Jupiter and Pluto stage three conjunctions this year, as Jupiter passes less than one degree north of Pluto at each conjunction on April 5, June 30 and November 12, 2020. (For reference, the moon’s angular diameter spans about 1/2 degree of sky.) All of these conjunctions in 2020 take place in front of the constellation Sagittarius, with Jupiter first passing Pluto on April 5 in prograde (going eastward in front of the backdrop stars), then sweeping past Pluto on June 30 in retrograde (going westward relative to the background stars), and then for the final Jupiter-Pluto conjunction on November 12 in prograde (eastward).

Sky chart of Sagittarius's teapot asterism, with the ecliptic line and an arrow pointing to a star.
All three Jupiter-Saturn conjunctions on April 5, June 30 and November 12, 2020, take place in front of the constellation Sagittarius, not far from the 5th-magnitude star 56 Sagittarii. Constellation chart via International Astronomical Union (IAU).

Most of the time, a Jupiter-Pluto conjunction in any year is a solitary event, as Jupiter laps Pluto going eastward, and never looks back. Triple conjunctions of Jupiter and Pluto – which occur over a period of about 7.4 months – are rare because Jupiter has to first catch Pluto going prograde (eastward), then in retrograde (westward) and then in prograde (eastward) again. The three-peat performance last happened in 1955-56 (November 2, 1955; February 8 and June 16, 1956), and will next occur in 2106-07 (July 13 and November 2, 2106; February 19, 2107). Yet, all three conjunctions in 1955-56 were widely spaced, and all three conjunctions in 2106-07 will be widely spaced, too.

Diagram of planetary orbits projected onto a vertical screen.
Illustration showing why a superior planet appears to go in retrograde (westward in front of the backdrop stars of the zodiac). As seen from the north side of the solar system, all the planets orbit counterclockwise. When the faster-moving Earth goes by a slower-moving superior planet, that planet appears to go backward (in retrograde). In 2020, Mars is in retrograde from September 9 to November 15, Jupiter from May 14 to September 13, and Saturn from May 11 to September 29. Image via Wikimedia Commons.

In other words, as we said above, 2020 may well showcase the best Jupiter-Pluto alignment for centuries to come. Most excitingly, both Jupiter and Pluto reached opposition in mid-July 2020. At opposition, a superior planet – any planet revolving around the sun outside Earth’s orbit – resides opposite the sun in Earth’s sky.

Diagram showing Earth between an outer planet and the sun.
Opposition happens when Earth flies between a superior planet, like Mars, and the sun. This happens yearly for most of the outer planets (and every other year for Mars). Illustration via Heavens-Above.

At opposition, a superior planet (or superior dwarf planet) rises at sunset and sets at sunrise, and is out all night long. It’s at opposition that a planet shines at its brightest best in Earth’s sky, and it’s at or near opposition that a planet comes closest to Earth for the year.

Jupiter reached opposition on July 14, 2020, at about 08:00 UTC, and was closest to Earth on July 15, 2020, at about 10:00 UTC.

Pluto reached opposition on July 15, 2020, at about 19:00 UTC, and was closest to Earth on July 13, 2020, at about 09:00 UTC.

In an uncanny bit of timing, the oppositions of Jupiter and Pluto happened almost concurrently in mid-July 2020. A planet reaches opposition midway through a retrograde. However, since Pluto resides so much farther from the sun than Jupiter does, Pluto’s retrograde lasts nearly 1 1/2 months (six weeks) longer than Jupiter’s four-month retrograde. So for near-unison oppositions, Pluto’s retrograde has to start – and end – approximately three weeks before – and after – Jupiter’s retrograde.

Jupiter and Pluto retrograde/opposition in 2020

Jupiter began retrograde: May 14, 2020, in front of the constellation Sagittarius
Jupiter at opposition: July 14, 2020, in front of the constellation Sagittarius
Jupiter ends retrograde: September 13, 2020, in front of the constellation Sagittarius

Pluto began retrograde: April 25, 2020, in front of the constellation Sagittarius
Pluto at opposition: July 15, 2020, in front of the constellation Sagittarius
Pluto ends retrograde: October 4, 2020, in front of the constellation Sagittarius

Jupiter-Pluto conjunction tables via Richard Nolle

Call it serendipity or synergy – or whatever – but the spectacular alignment of the king planet Jupiter with the dwarf planet Pluto doesn’t get much better than in 2020. A similarly good Jupiter-Pluto rendezvous might not happen again for a number of centuries to come.

Scattered bright dots of stars with one small dot marked, the planet Pluto.
Pluto as seen with a 12″ S/C telescope (14.3 mag.) on July 10, 2015. Photo by Efrain Morales of Sociedad de Astronomia del Caribe. More information about Pluto’s current location.

Bottom line: Jupiter is as easy to find as the dwarf planet Pluto is difficult. Jupiter is bright! It ranks as the fourth-brightest celestial object to light up the heavens, after the sun, moon and Venus. Pluto, on the other hand, is 1,600 times dimmer than the faintest star visible to the unaided eye. But Jupiter can help you find – or at least envision – Pluto this year. That’s because these two worlds are having a triple conjunction this year; they’re near each other on the sky’s dome all year and will come exceptionally close three times in 2020.

November 4, 2020
Astronomy Essentials

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