Get ready: The conjunction queries are inbound. “Did you see those two bright things in the sky last night?” Says a well-meaning family member/friend/coworker/random person on Twitter who knows you’re into astronomy. “They were HUGE!”
That’s right. It’s time for Jupiter and Venus—the fourth and third brightest objects in the sky, respectively—to meet up. The conjunction occurs low in the dusk sky with Jupiter receding in the distance, while speedy Venus heads towards overtaking the Earth on the inside track of the inner solar system in 2020.
The actual conjunction occurs on Sunday, November 24th at ~13:00 Universal Time (UT)/9:00 AM Eastern Standard Time (EST) with -3.9 magnitude Venus just 1.4 degrees south of -1.8 magnitude Jupiter. You’ll be able to watch the approach this week going into the weekend as the distance between the pair shrinks by about half a degree (the span of a Full Moon) per day.
Conjunctions between Jupiter and Venus aren’t all that uncommon. On average, such a pass occurs roughly once a year, mainly a function of the 399 synodic period of Jupiter as it completes one circuit around the starry background, passing Venus in either dusk or dawn.
It always amuses us how folks will say ‘large’ describing an object in the sky, when they actually mean ‘bright.’ What’s more, astronomy and knowledge of the sky can save lives, or at least, prevent international incidents. For example, in 2013 Indian Army patrols near the Chinese border reported seeing suspicious activity towards dusk from one evening to the next, activity revealed by Indian Institute of Astrophysics astronomers to be—you guessed it—a close conjunction of Venus and Jupiter, similar to the one we’re seeing this week. Another astronomical event nearly triggered the apocalypse on the night of October 5th, 1960, when an automated Distant Early Warning system mistook the rising Moon for a Russian missile launch.
…and the Moon Makes Three
Speaking of the Moon, the razor thin waxing crescent Moon will join the pair next week, turning the twosome conjunction into a trio grouping. The Moon passes New on November 26. On the evening of November 27th the Moon is a tough catch, seven degrees to the lower right of Jupiter as a 2% illuminated crescent, only 31 hours old for the U.S. East Coast; the Moon is much easier to see on the evening of the 28th as it sits just above Venus and the Moon.
Observers living in northeastern India, Nepal and Tibet will also see a very special event on the evening of the 28th, when the Moon occults (passes in front of) Jupiter. Watch for the Coleridge Effect, an illusion where Jupiter seems to ‘hang’ stationary on the dark limb of the Moon before disappearing entirely. This term comes from Samuel Coleridge’s tale (cue Iron Maiden) The Rime of the Ancient Mariner, which describes ‘one bright star, almost atween the tips… of the horned Moon.”
At the eyepiece, Venus presents a 90% illuminated, 12 arcsecond gibbous disk this week, while stately Jupiter spans 32” across. Keep an eye on Jove, as the moons Io and Europa both cast shadows back on the Jovian cloud-tops from on November 22nd 00:18 to 00:37 UT. Jupiter’s outermost Galilean moon Callisto is also getting back into the shadow-casting act, as part of a new cycle. Fun fact: Callisto is the only one of the four Galilean moons whose shadow can ‘miss’ Jupiter. We’re ending just such a ‘Callisto shadow drought’ this month.
Wind the celestial clock forward, and truly bizarre events can occur. Stick around until November 22nd, 2065, for example, and you can see Venus pass in front of Jupiter.
An event slightly closer in time involves a simultaneous occultation of Venus and the bright star Regulus on September 19th, 2025, though you’ll have to venture to northern Siberia to see it! Such an ’emoticon conjunction’ presents us with a ‘celestial smile’ made up of a planet and a bright star Paired with the crescent Moon, suggesting that perhaps, the Universe does indeed have a sense of humor.
After this month’s pairing, Venus goes on to rule the dusk sky in 2020, reaching greatest eastern elongation 46 degrees from the Sun on March 24th. Meanwhile, Jupiter sinks into the dusk in December, lost as it heads towards solar conjunction on December 27th.
Catch ‘em now, as one of the last great planetary pairings of 2019.