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Bruce BettsNovember 7, 2019

How to See the 2019 Mercury Transit

What is happening?

A rare transit of Mercury across the Sun occurs 11 November 2019. Here's a guide to when and how to observe the planet's small disk crossing in front of the Sun. Check it out if you can—the next Mercury transit isn't until 2032!

What is a transit?

A transit in this context is when one celestial body (e.g., Mercury) passes in front of another body (e.g., the Sun) and blocks a small portion of it as seen from a third celestial body (e.g., Earth).

What is a Mercury transit?

A Mercury transit of the Sun as seen from Earth occurs when the Sun, Mercury, and Earth line up so that Mercury appears in front of the Sun as a small black disk moving across the Sun for several hours.

How often and when do Mercury transits occur?

Mercury transits occur about 13 to 14 times per century. The last one was in 2016, but the next isn't until 2032. The timing is tied to not only the interplay of the orbital periods of the two planets, but also the relative tilt of the two orbits. Mercury's orbital plane is tilted a few degrees relative to Earth's orbital plane. The Sun-Mercury-Earth line-up can only occur when Mercury is passing through the plane of Earth's orbit, and only if that occurs when Earth is in the right part of its orbit. Random Space Fact: currently Mercury transits can only occur during May or November. Those are the times in Earth's orbit when Mercury can line up with the Sun IF Mercury is at the right point in its orbit.

Mercury and Earth Alignments

European Southern Observatory

Mercury and Earth Alignments
Because Mercury and Earth have different orbital tilts, a Mercury eclipse as seen from Earth can only occur at very specific times during May or November.

From where is the 11 November 2019 Mercury transit visible?

This transit will be visible from South America and Africa, and most of North America and Europe. All that is required for you to see it is that it's daytime at your location. For Europe and most of Africa, the Sun will set while the transit is still occurring. For the east coast of North America and all of Central and South America, the entire transit will be visible. For central and western North America, the Sun will rise with Mercury already in transit.

Mercury Transit 2019 Visibility

Eclipsewise.com

Mercury Transit 2019 Visibility
This map shows regions of Earth where the 2019 Mercury transit will be visible.

What time is the 11 November 2019 Mercury transit?

Here's a handy table to help you out. The start time is when Mercury just broaches the edge of the Sun, and the end is when it moves off the Sun on the opposite side.

UTCESTPST
Start of transit 12:35 7:35 4:35
Middle of transit 15:20 10:20 7:20
End of transit 18:04 13:04 10:04

How can I observe the transit safely?

Because of Mercury's small size and substantial distance from Earth, it will require a telescope to see. When using a telescope, it is crucial to use proper safety filters over the front of the telescope or you risk serious eye damage. Do NOT look through a telescope, a telescope's finder scope, or binoculars (or with just your eyes) at the Sun without filters designed for solar viewing, such as those that can be obtained from reputable telescope makers. If you are unsure whether you have the right equipment, try to find a public viewing in your area. You can also watch live streams from several telescopes around the world, right from the comfort of your own home!  These include the following:

What will the Mercury transit look like?

With a small telescope, Mercury will be a tiny dot on the Sun moving across the whole face of the Sun over the several hours of the transit. A larger telescope will distinguish Mercury as a black disk, but it will still be tiny compared to the Sun. Frankly, the view of the transit is not visually spectacular. There's a little black spot on the Sun. What is spectacular is that you are viewing another planet tens of millions of kilometers away passing directly in front of the Sun (ponder that)! You are witnessing a rare celestial event that won't occur again until 2032.

Mercury Transit, 2016

NASA / Bill Ingalls

Mercury Transit, 2016
Mercury transits the sun on 9 May 2016, as seen from Boyertown, Pennsylvania. Mercury is available as a small dot at about 7 o'clock, halfway from the center of the sun. Some small sunspots are also visible.

Do any other planets transit the Sun as seen from Earth?

Venus also transits the Sun as seen from Earth, but Venus transits are even rarer. The last one was in 2012 but the next one will not occur until 2117.

Have we ever observed a planetary transit from another planet?

The Curiosity rover made the first observation of a planetary transit from the surface of another planet when it observed a Mercury transit from Mars in 2014.

Have we ever observed other kinds of transits from other places or worlds?

Sometimes, our spacecraft elsewhere in the Solar System see transits due to their unique geometries. NASA's Sun-observing STEREO spacecraft saw a Mercury transit in 2013. The Mars Exploration Rovers and Curiosity have seen transits of Mars' moons across the Sun.

Curiosity sees a Phobos transit, sol 369

NASA / JPL / MSSS / TAMU / Emily Lakdawalla

Curiosity sees a Phobos transit, sol 369
Curiosity watched Phobos pass across the Sun on sol 369, shooting one photo per second. This animation runs about 10 times natural speed.

Finally, one of the ways we learn about exoplanets is by watching them cross in front of their host stars! We can't see exoplanets as a single disc like Mercury, but we know they are there due to temporary dips in their stars' light.

Read more: eclipses and transits, Mercury

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Bruce Betts

Chief Scientist / LightSail Program Manager for The Planetary Society
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