Just a few days to go for the most awaited astronomical event of this year, the great conjunction. The year 2020 was an excellent year for those who love sky-gazing. Some of the exciting astronomy events were: Annular Solar Eclipse on the day of the summer solstice, the four lunar occultations of Mars, the appearance of comet NEOWISE, the closest approach of Jupiter and Saturn in the same week, and the special opposition of Mars in October. But that’s not all. Before 2020 ends, there’s another reason to look up, and that is the great conjunction.
What Is Great Conjunction?
Astronomers use the word conjunction to describe two celestial objects’ close approach as seen from the Earth. Great conjunction refers to Jupiter and Saturn’s close approach, two of the biggest worlds in our solar system. This year, it will take place on December 21, on the day of the winter solstice.
The rarity of great conjunctions is due to the slow-motion of Jupiter and Saturn across the sky. Among the planets visible to the naked eye, they are the two most distant from the Sun, taking 11.86 years and 29.5 years respectively to orbit it. As the two planets gradually move through the constellations at different speeds, they follow almost the same path across the sky, called the ecliptic. Annually, Jupiter completes 30 degrees of its orbit around the Sun. On the other hand, Saturn sweeps 12 degrees. Thus, Jupiter reduces Saturn’s gap and itself by (30-12) 18 degrees every year. So Jupiter laps the ringed beauty every 20 years on average.
On 21 December at 13:30 UT, Jupiter will be 0.1° south of Saturn. The gas giant will appear together in a telescopic view. It’ll be the first Jupiter-Saturn conjunction since the year 2000 and the closest Jupiter-Saturn conjunction since March 1226. The next conjunction will take place in 2040. But this year’s conjunction won’t be matched until March 15, 2080.
The previous great conjunction took place in 2000 when both the planets were close to the Sun, making it almost invisible with the naked eye. This year, we have a great chance as the planets lie 30° east of the Sun.
How To Watch The Great Conjunction?
The great conjunction is not an event that will occur for a few minutes, as the total solar eclipse. You don’t have to wait for the exact moment on December 21. They’re visible tonight and every night – near each other for the rest of 2020 – an appealing and mind-expanding sight!
Jupiter and Saturn become visible in the south-western horizon in the constellation of Sagittarius as shown in the image above. In December, they will lie in Capricornus. The brighter one is Jupiter. It is brighter than any other star in the night sky.
As earthsky notes, this next month – from October 21 to November 21, 2020 – Jupiter will travel about 5 degrees on the sky’s dome, while Saturn will travel about 2 degrees in the sky. So Jupiter will gain 3 degrees on Saturn, and the two gas giant planets will be some 3 degrees apart as of November 21, 2020.
The following month – November 21 to December 21, 2020 – Jupiter will travel about 6 degrees and Saturn 3 degrees. That means Jupiter will have bridged the 3-degree gap that had existed between the king planet and Saturn on November 21, 2020. From October 21 to December 21, 2020 – Jupiter will have traveled 11 degrees and Saturn 5 degrees.
What’s More In December?
Though the great conjunction is the flagship astronomical event in December 2020, the month is packed with many other celestial events. It has the best meteor shower – the Geminids, a total solar eclipse, the lunar occultation of Venus, and the winter solstice day. Watch the video embedded above for all the top astronomical events in the last month of the year!