On April 28, Earth will be exactly in between the sun and Saturn. Called ‘Saturn opposition’, this day is when Saturn is the closest to Earth in the whole year.

Two celestial bodies (in this case the sun and Saturn) are said to be in ‘opposition’ when they are on opposite sides of the sky when viewed from Earth.

When in opposition, Saturn will appear disc-like and be fully illuminated by the sun. This makes it the most convenient day in the year for astronomers and star-watchers to observe the planet, said Dr. P. Iyamperumal, Executive Director of the Tamil Nadu Science & Technology Centre.

Though Saturn can be seen with the naked eye as a bright non-twinkling star, Dr. Iyamperumal recommends a simple telescope or a pair of good binoculars. “Only then will we see the planet in all its glory, its rings and perhaps even some of its satellites.”

Since its orbit around the sun is much larger, and it moves much slower than the Earth (Earth moves in orbit at 29.78 km per second in contrast to Saturn’s 9.69 km per second), Saturn takes about 29.5 Earth years to complete one revolution.

As a result, every 378 days, the Sun, the Earth, and Saturn are perfectly aligned. On April 28, Saturn will rise at sunset directly opposite to the Sun, be visible all night, and set at sunrise on the 29 in the west.

Closest encounter

Opposition occurred last year on April 15 and will occur next year on May 10. Though this is a yearly phenomenon, 2013’s Saturn opposition is a little extra special because this will be the closest Earth-Saturn encounter until 2023.

Saturn will be only about 132.2 crore km away from Earth, he said, as compared to about 165 crore km at its farthest.

Moreover, during this opposition, Saturn’s rings will be tilted 18 degrees making it easier to see than if it was edge-on.

Interestingly Galileo had a similar view of Saturn back in the 17 C, only he wrongly guessed that the rings were two moons on either side of the planet. It was only decades later that Dutch astronomer Huygens identified Galileo’s “moons” as a ring system.

As interesting as Saturn’s opposition may be to the average astronomy enthusiast, the phenomenon is not of utmost significance as far as scientists studying the planet and its rings are concerned.

“Opposition is a purely geometric event,” stressed Dr. Rajaram Nityananda, astrophysicist and Senior Professor at TIFR. “This is not particularly more helpful for observations than even a month on either side.”

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