The planet Mercury passed directly across the face of the Sun for the first time in 10 years, as it casts a shadow across South America, Africa, Western Europe and the east of North America.
Mercury, which is slightly larger than the Earth’s moon, is too small to see without binoculars or a telescope, and experts warn that looking directly at the Sun during event could damage eyes.
Although the event is of limited scientific value, it does provide an opportunity to learn about the solar system.
Seeing the silhouette of a planet in motion in front of the Sun is a clear demonstration of the solar system in action.
The transit is also an example of how scientists detect planets in other solar systems, where they are mostly hard to see because they are lost in the glare of the star they circle.
The Kepler observatory has detected more than 1,000 of these by looking for the small but characteristic dip in brightness as a planet passes directly between its star and the Earth.
Since the last time Mercury transited the Sun, NASA’s Messenger spacecraft spent four years orbiting around the planet, before being deliberately crashed into its surface last year.
The mission revealed Mercury’s moon-like surface in unprecedented detail, scarred by the collision of asteroids and meteorites.
It also mapped ancient lava flows and discovered what is believed to be ice at the planet’s poles.
Planets in our own solar system are particularly helpful, because we can see them close up and learn vastly more about their similarities and differences than is possible for more distant planets.
On average, transits of Mercury occur about 13 or 14 times every 100 years. The last one took place in 2006, and the next one won’t occur until November 11, 2019. After that, we won’t see another until 2032.