On Monday, Nov. 11, skywatchers throughout the United States and much of the Western Hemisphere will have a chance to see the elusive planet Mercury in broad daylight. This is not because it will shine so brilliantly; instead, it will appear completely black!
On that morning, the planet will drift in front of the sun and appear in silhouette against the sun’s intensely bright face. This is known to astronomers as a transit of Mercury.
The phenomenon is unlike a solar eclipse because Mercury will appear quite tiny — only 1/158 of the sun’s diameter; to see its tiny silhouette against the sun’s brilliant face, you will need a telescope with a power of at least 50x. Like a solar eclipse, however, you must take special care to protect your eyes.
Never look in the direction of the sun with an unfiltered eye, binoculars or telescope, and never use homemade filters such as sunglasses, double thickness of darkened film, smoked glass, uncoated mylar, tinted glass and others.
While these may appear to reduce the sun’s glare, they will not cut the invisible radiation (infrared and ultraviolet) that can burn your eyes without your knowledge. Only proper solar filters are safe, and you can find them at sources listed on the MrEclipse.com website.
As Mercury orbits the sun every 88 days, it appears to transit the face of the sun about 13 times each century. Mercury last crossed the sun in 2016 and won’t do so again until 2032; unfortunately, we in North America must wait until 2049 for our next view of a Mercury transit. So, if the sky is clear on Nov. 11, be sure to check out this amazing and rare sight.
The transit will begin around 4:35 a.m. PST and will be entirely visible to skywatchers in eastern North America and all of South America. In western North America and much of the Pacific, however, the transit will be underway as the sun rises, while viewers in Europe and Africa will see the sun set with the transit still in progress.
Your first indication that the transit has begun will be the appearance of a tiny notch on the eastern edge of the sun. During the morning hours, the planet’s silhouette will appear to drift slowly westward across the face of the sun, reaching its midpoint around 7:20 a.m. PST.
It will appear to leave the sun’s disk at around 10:04 a.m. PST. Click here to check out Tables 2 and 3 at the EclipseWise website to find the transit times for various cities in the United States and Canada.
Keep in mind that no celestial phenomenon is worth risking your vision. Unless you have a telescope and are positive that you have a proper solar filter that is fitted over the front end of the instrument, I recommend you check with your local science museum, planetarium or amateur astronomy club to learn who will be setting up public telescopes that day.
However you choose to watch it, be safe, and enjoy this rare sky show!
— Dennis Mammana is an astronomy writer, author, lecturer and photographer working from under the clear dark skies of the Anza-Borrego Desert in the San Diego County backcountry. Contact him at email@example.com and follow him on Twitter: @dennismammana. The opinions expressed are his own.