A few weeks ago, on December 21, 2020, we got to see Jupiter and Saturn’s closest approach after 800 years. The two large gas giants of the solar system were just 0.1 degrees apart, as seen from the Earth. The great conjunction delighted astronomers and space enthusiasts around the globe. But now, get ready to observe the rare triple conjunction of planets as the pair of gas giants is getting closer to the tiniest planet of our solar system, Mercury. The first part of this article explains what will happen in the solar system, and the second part is on watching the triple conjunction with naked eyes.
What’s going on?
Before we try to understand what is happening in the solar system, let me introduce you to two technical terms often introduced in planetary science: opposition and conjunction.
An opposition occurs when the Sun, the Earth, and a superior planet come in a straight line, with the Earth in the middle, as shown in the illustration above. Note that at the opposition, the planet is opposite to the Sun. In 2020, Saturn and Jupiter were at opposition in July. When a planet is at this position, it rises in the east at sunset, reaches its highest point in the sky around midnight, and sets in the west at dawn. At around the same time, the planet makes its closest approach to the Earth. So, it’s the best time to photograph the planet as it is at its brightest.
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As months go by, the planets’ movement takes them to the opposite part of the solar system, as seen from the Earth. When the Sun, the Earth, and a superior planet come in a straight line, this time, with the Sun at the center, it is known as solar conjunction. As shown in the illustration, the planet lies at its most distant point from the Earth. Due to its apparent proximity to the Sun, it rises and sets around the same time as the Sun. When a planet is at solar conjunction, it is lost in the Sun’s glare.
It has been about six months since the two beasts were at opposition. They are getting closer to the Sun as seen from our planet. On the opposite side of the solar system, are going to (imperfectly) line up with Mercury as shown below.
The image compares the position of the planets on the Great Conjunction of 21 December 2020, and on the triple conjunction on 10-11 Jan 2021. Since the gap between Jupiter and Saturn has widened, the four planets won’t align on the same day.
How to watch the triple conjunction?
On January 10, look in the south-west direction as the dusk sky fades. Mercury will pass 1°39′ to the south of Saturn. The brighter of the two will be Mercury at a magnitude of -0.9 compared to Saturn’s +0.6. The pair will be too widely separated to fit in a telescopic view but will be visible to the naked eye or through a pair of binoculars. Be careful while pointing your telescope at the two planets. They are close to the Sun. Attempting to look at the Sun with a telescope without a solar filter can damage your eyes. Jupiter will be above the two planets, forming a perfect triangle in the evening sky, as shown below.
The next evening, on January 11, Jupiter will pass 1°28′ to the north of Mercury. The pair will be about 8 degrees above the ground as the dusk sky fades. Of all the three planets, Jupiter will be the brightest, followed by Mercury and Saturn. They will be in the constellation of Capricornus. Even on January 11, the planets won’t fit together in a telescope view as the triple conjunction of January isn’t a perfect alignment of the planets. The illustration of the sky is shown below. To clearly show the planets, daylight has been removed from these pictures.
What’s more in 2021?
2021 has many fascinating astronomical events for us. For a complete list, you can watch the ‘Astronomy Calendar 2020’ here. In another video (given below), I have presented the 10 rare celestial events that will occur this year.