May 9 Mercury Transit Will be the Decade's Most Adorable Eclipse: How to Watch

Mercury's transit is rare and wondrous, but not worth going blind for.

by Kastalia Medrano
Xavier M. Jubier

Don’t look up, but beginning in the early morning of May 9, Mercury will pass between the Earth and the Sun, blacking out a tiny speck (1/160th of the Sun) of sunlight. The event is known as the transit of Mercury, which is a roughly once-in-a-decade astronomical phenomenon and also a potentially decent album title for indie band.

Staring directly at the sun is obviously a bad idea, but you can view the event yourself with some special equipment. A telescope with a high-quality solar filter (one that filters the light before it enters the scope, not before it reaches your eye) is your best bet. You can also use your telescope to project an outline of the sun onto white paper a couple feet away, although this method runs the risk of serious burns and/or things catching on fire.

If you don’t have a telescope, you can watch an HD livestream from Sky & Telescope.

Eastern North America, virtually all of South America, and western Europe and Africa are positioned to view the transit. Here’s when to watch it in America:

When to watch the transit of Mercury, based on time zone. The * means the transit begins before sunrise.


The most interesting parts of the transit are at the beginning and the end, when Mecury interacts with the edges of the sun in a teardrop-shaped optical illusion called the “black drop effect.” Each transition lasts about three minutes, 15 seconds. This is caused because the Sun’s outer edge appears darker than the rest of the Sun.

While it takes more than seven hours for Mercury to pass in front of the sun, the planet, which is less than half the size of earth, is moving fast: 30 miles per second, or 108,000 miles per hour.

May and November are the most common months for this moment in Mercury’s orbit, according to Slooh. The last such transit was in 2006. The next transit of Mercury is November 11, 2019, which will be visible to people in Europe and the Americas. The ones after that won’t occur until 2032 and 2039, and these will not be visible from North America. So, after 2019, American observers will have to wait until 2049.

Although transits of Mercury are less dramatic than those of bigger, closer Venus, they occur more often — about 13 or 14 times per century. (The next transit of Venus won’t happen until 2117.)

The last time Mercury passed between the sun and Earth was in 2006


“The transit of Mercury reminds us that all of the planets, including Earth, are in rapid and perpetual motion,” said Paul Cox said of the Slooh robotic telescope service, which is also livestreaming the event. “As we gaze together at this majestic astronomical event, we will appreciate that it is similar planetary transits around other stars that have allowed us to discover a multitude of strange and exotic exoplanets.”

Also, to clear up any confusion: Mercury is also in retrograde, but that is not what this is. Retrograde is what happens when the movement of a planetary body appears to switch direction from the perspective of Earth, because of their relative orbits. This is a totally separate phenomenon, on which you cannot blame your fender bender or bad Tinder date or whatever it is people like to blame on the retrograde.

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