This week, Venus and Jupiter are very low in the southwest during the chilly November dusk. When the month began, they were widely separated, by nearly 24 degrees. Your clenched fist held at arm’s length measures roughly 10 degrees, so the two brightest planets appeared about two and a half fists apart.
But in the days that followed, the two planets have been approaching each other, getting closer by about 1 degree each day. When they overtake each other this weekend, the meeting will be further enlivened by background stars and the passage on Thanksgiving evening of a foreground waxing crescent moon.
Both planets are moving eastward with respect to the stars, with the slowest, Jupiter, initially in the lead and the faster Venus in the rear. Thus, November began with a diagonal line of Jupiter and Venus (from upper left to lower right) along the ecliptic, that imaginary line on the sky that marks the annual path of the sun, as well as where the moon and planets wander. At the start of this month, Venus was setting less than an hour after the sun.
But with each passing day, Venus has slowly been getting higher. And with each passing day, the excitement has grown as the gap between Venus and Jupiter has rapidly shrunk.
Two planets passing in the twilight
Sunday (Nov. 24) evening, Jupiter and Venus appeared nearest to each other, though they were less than one-tenth of a degree closer compared to the previous night, with Venus sitting to Jupiter’s lower left. The pair will remain side by side in the evening sky this week, with Venus slowly drifting to the south (left) and Jupiter drifting north (right).
No doubt, these two worlds will call attention to themselves, even for people who normally don’t pay much attention to the sky, as the planets appear low in the southwest twilight sky shortly after sunset this week. Jupiter easily rivals Sirius, the brightest of all stars, and Venus appears seven times brighter than Jupiter.
If you check out these two planets through a telescope, you’ll see that Jupiter appears as a full disk, nearly three times larger than Venus, which itself is 90% illuminated. Venus appears far more dazzling than Jupiter. That’s partly because the former is four times closer to Earth than Jupiter, but also because Venus is more than seven times closer to the sun than Jupiter and is receiving a more intense dose of reflected sunlight.
A 24-year cycle
Conjunctions between Venus and Jupiter are not rare; the planets pair off about once a year. However, there is an interesting 24-year cycle in which these two planets replicate a get-together. This happens because Venus and Earth engage in an 8:13 resonance, in which eight revolutions of the Earth around the sun take almost exactly the same amount of time as 13 revolutions of Venus around our star. So, Venus appears at practically the same spot on the sky after eight years. Meanwhile, it takes Jupiter 11.86 years to make one trip around the sun. Double that, and you get nearly 24 years.
So about every 24 years, Venus and Jupiter return to the same part of the sky and appear in conjunction once again.
Below is a list of dates for these special 24-year conjunctions:
Nov. 9, 1947 Nov. 14, 1971Nov. 19, 1995Nov. 24, 2019Nov. 29, 2043Dec. 5, 2067 Dec. 11, 2091
Notice how these Venus-Jupiter pairings occur five or six days later in the calendar at the 24-year intervals. The last one of these conjunctions was in 1995, and the next will be in 2043.
Turkey day tableau
Instead of an after-dinner mint on Thanksgiving Day (Nov. 28), how about indulging in a celestial treat that evening?
In the southwest skies, we will still be able to enjoy the sight of Venus and Jupiter, now separated by nearly 5 degrees, but now also joined by a lovely waxing, crescent moon, just a little over two days past new phase. The moon will appear to hover just 1.5 degrees above Venus. The show will run from sunset to about 6 p.m. local time. But the best time to see all three will come about 30 to 45 minutes after sunset, when they’ll appear against the deepening cobalt blue of evening twilight.
Look carefully and see if you can make out the entire disk of the moon, with the dark portion immediately straddling the bright, slender sliver. The rest of the lunar disk will seem to dimly glow with an eerie bluish-gray coloration. This is earthshine. An astronaut standing on the dark part of the moon would see a nearly full Earth in the sky; sunlight reflected off of the planet would provide the only illumination for the surrounding lunar landscape. That’s the faint blue-gray light you’re seeing from here on Earth. In binoculars or a small telescope, the moon will appear more textured and 3D, like some translucent Christmas ball.
And if you would like to see more moons, train your telescope on Jupiter; all four of the famous Galilean satellites will be aligned on one side of the giant planet. Farthest from Jupiter will be Callisto; then comes Ganymede, while much closer to Jupiter will be Europa and Io.
In all, a great way to put the topper on the holiday.
Joe Rao serves as an instructor and guest lecturer at New York’s Hayden Planetarium. He writes about astronomy for Natural History magazine, the Farmers’ Almanac and other publications. Follow us on Twitter @Spacedotcom and on Facebook.
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