NASA has published a film showing Mercury transiting the sun – passing between it and the Earth.
The video shows the silhouetted planet – which is the smallest in the solar system, and the closest to the sun – passing across the face of it.
The last time Mercury passed between the Earth and the sun was on 9 May 2016, and the next won’t be until 13 November 2032.
The first time a transit was ever observed was on 7 November 1631, although one of the fathers of modern astronomy Johannes Kepler predicted the existence of these transits before.
Astronomers consider the transits to be important for two special developments in astronomy.
Kepler had predicted that planets orbited the sun in elliptical shapes, rather than perfect circles, running contrary to the previous theories of the solar system – believed to revolve around the Earth.
“Transits of Mercury and Venus can happen because they are the only planets that orbit between the Earth and the sun,” NASA said.
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“By using ellipses to describe the orbits of the planets Kepler was able to predict when transits would occur.
“The Ptolemaic theory that used circular orbits did not have the accuracy needed to predict these events, even after epicycles and equants were introduced.
“In 1627, Kepler predicted that a transit of Mercury would occur on November 7 1631. Pierre Gassendi watched from his Paris observatory and saw a small black dot move across the face of the sun on that day.”
From the surface of Mercury, the sun would appear three times larger than it does in the Earth’s sky, and the sunlight would be seven times brighter.
However because it has no atmosphere, Mercury does not retain the sun’s heat on its dark side – this means that Venus, which has a dense atmosphere, is the hottest planet in our solar system.
Two spacecraft have visited Mercury, the Mariner 10 in 1974 and Messenger, which was launched in 2004
The most colourful images of Mercury were produced by using images from the Messenger spacecraft.