A Transit of Mercury Happens Nov. 11

The sky will put on a show Nov. 11 when Mercury journeys across the Sun. The event, known as a transit, occurs when Mercury passes directly between Earth and the Sun. From our perspective on Earth, Mercury will look like a tiny black dot gliding across the Sun’s face. This only happens about 13 times a century, so it’s a rare event that skywatchers won’t want to miss! Mercury’s last transit was in 2016.  The next won’t happen again until 2032!

“Viewing transits and eclipses provide opportunities to engage the public, to encourage one and all to experience the wonders of the universe and to appreciate how precisely science and mathematics can predict celestial events,” said Mitzi Adams, a solar scientist in the Heliophysics and Planetary Science Branch at NASA’s Marshall Space Flight Center in Huntsville, Alabama. “Of course, safely viewing the Sun is one of my favorite things to do.”

This year’s transit will be widely visible from most of Earth, including the Americas, the Atlantic and Pacific Oceans, New Zealand, Europe, Africa, and western Asia. It starts at about 6:35 a.m. CST, but viewers in some areas, such as the West Coast, will have to wait until the Sun rises at their location to see the transit already in progress. Thankfully, this transit will last almost six hours, so there will be plenty of time to catch the show. At about 9:20 a.m. CST, Mercury’s center will be as close as it is going to get to the Sun’s.

Mercury’s tiny disk, jet black and perfectly round, covers a tiny fraction of the Sun’s blinding surface — only 1/283 of the Sun’s apparent diameter. So you’ll need the magnification of a telescope (minimum of 50x) with a solar filter to view the transit. Never look at the Sun directly or through a telescope without proper protection. It can lead to serious and permanent vision damage. Always use a safe Sun filter to protect your eyes!

Scientists have been using transits for hundreds of years to study the way planets and stars move in space. Edmund Halley used a transit of Venus in 1761 and 1769 to determine the absolute distance to the Sun. Another use of transits is the dimming of Sun or star light as a planet crosses in front of it. This technique is one way planets circling other stars can be found. Scientists can measure brightness dips from these other stars (or from the Sun) to calculate sizes of planets, how far away the planets are from their stars, and even get hints of what they’re made of.

Five Planets Align in Early Morning Sky

The graphic below illustrates the five planets as they are visible, with the naked eye, from Huntsville, Alabama.  It shows their positions in the sky around 6:30 AM during the week of January 18 and continuing for the next few days. Mercury will be close to the Sun, over in the East, and Jupiter will be over in the West, with Venus, Saturn, and Mars between the two. Pluto is near Mercury, but is invisible to the eye, requiring a telescope for viewing.

The last time an alignment such as this occurred was about 10 years ago. This pre-sunrise configuration will be similar for other northern latitudes.

In the graphic, the yellow line is the ecliptic, which is the plane of the Earth’s orbit. The orbits of the major planets lie close to this plane, which is why they appear close to the ecliptic in the night sky.

Image generated by Bill Cooke using SkySafari Pro software.
Image generated by Bill Cooke using SkySafari Pro software.

Mercury Visible After Sunset

NASA’s Mercury MESSENGER spacecraft is preparing to insert itself into orbit tonight, Mar. 17. While you may not have a seat, you can still see Mercury tonight after sunset from the comfort of planet Earth.


Close-up image of a portion of Mercury’s surface, captured on a MESSENGER fly-by
on Oct. 6, 2008. (NASA/Johns Hopkins University Applied Physics Laboratory/
Carnegie Institution of Washington)

The key to seeing Mercury is having an unobstructed view of the horizon in the sunrise or sunset direction. You should look for Mercury about 30 to 40 minutes after sunset, as soon as the sky begins to darken.

For more viewing information about Mercury and other skywatching opportunities, visit: http://www.skyandtelescope.com/observing/ataglance

Keep up on the latest progess of Mercury MESSENGER at NASA’s MESSENGER mission page: https://www.nasa.gov/mission_pages/messenger/main/index.html

and the Johns Hopkins University Applied Physics Laboratory Website: http://messenger.jhuapl.edu/