The two biggest planets of our solar system - Jupiter and Saturn - will form 'The Great Conjunction' in the evening sky tonight. Tonight, December 21, also marks the annual winter solstice - the longest night of the year - in the Northern Hemisphere.
What is 'The Great Conjunction'?
"You can imagine the solar system to be a racetrack, with each of the planets as a runner in their own lane and the Earth toward the center of the stadium," Henry Throop, an astronomer in the Planetary Science Division at NASA Headquarters said in Washington, in order to explain what a conjunction in general is. When planets align with each other on their respective orbits and pass each other, a conjunction takes place.
"From our vantage point, we'll be able to see Jupiter on the inside lane, approaching Saturn all month and finally overtaking it on December 21," added Throop. The conjunction could have been seen as a bright "Christmas Star" in the evening sky for the past two weeks, with 'The Great Conjunction,' where Jupiter overtakes Saturn, culminating tonight.
The positions of Jupiter and Saturn aligned in the sky about once every 20 years, however tonight marks a special event in that the last time the planets were aligned so close to each other was in the year 1623. It has also been 800 years since the alignment of the biggest gas balls occurred in the night sky. This event occurring in 2020 will enable the global viewing of the conjunction.
"The distance between the planets will remain (the) same but the angle of viewing it from Earth will be aligned. From the Earth, the two planets will be viewed only 0.1 degrees apart," said Dr. Yashwant Gupta, Director of National Centre for Radio Astrophysics (NCRA).
When and how to watch 'The Great Conjunction'?
Dr Gupta informed that the conjunction can be viewed shortly after sunset on Monday. "By 7:30 pm, both the planets will be visible low on the horizon as they will set down like the sun." he said.
Despite appearing super close, Jupiter and Saturn will actually be more than 730 million kilometers apart. While the conjunction can be seen with the naked eye, a telescope can better capture the field of view, while also showing some of the planets' brightest moons.
This event is expected to occur next in March 2080.
According to NASA, an unobstructed view of the sky is sufficient to view the conjunction from most cities given that both planets are quite bright. The phenomenon can be viewed post sunset in the southwestern sky. While Jupiter will be easier to spot, appearing like a bright star, Saturn will be fainter and placed toward the upper-left of Jupiter. To distinguish the planets in an easier fashion, as well as to view Jupiter's large moons, the use of binoculars or a telescope is recommended.