Mercury will make a rare pass directly between the Earth and the sun on Monday.
It will appear as a small black dot at the edge of the sun about 7:12 a.m. and slowly cross the sun’s face over the next 7 1/2 hours, reaching the other side at 2:42 p.m., according to NASA.
Such transits of Mercury, as the phenomenon is known, occurs about 13 times a century. This one will be the first since 2006 and the last until 2019.
“Scientifically, it’s not important as it was centuries ago,” said Nancy Chabot, a planetary scientist at the Johns Hopkins Applied Physics Laboratory in Laurel and an instrument scientist on NASA’s Messenger mission to Mercury.
Still, she said, “it’s definitely fun. It’s a rare event that happens that you can see a planet highlighted agains the disk of the sun.”
As early as the 1600s, measurements taken during transits of Mercury and Venus helped scientists estimate the sizes and distances of objects in the inner solar system. Today, they still have some scientific value -- several NASA satellites will be watching and using the transit to calibrate their bearings.
A transit of Venus occurred in 2012, but that planet won’t cross the sun’s face again for another century.
Do not try to watch the Mercury transit with the naked eye – both because it’s unsafe to look directly at the sun and because the dot will be too tiny to see, anyway. It can be seen with powerful binoculars or a telescope, but only one equipped with proper solar filters.
Or, just follow it live on NASA TV or at nasa.gov/transit. Mercury will take a diagonal path across the lower half of the sun.
The Maryland Science Center is holding a free viewing event using its own telescope from 10 a.m. to 3 p.m. Brett Denevi, a colleague of Chabot’s on the Messenger mission, will be on hand to answer questions about Mercury.
The entire transit will be visible from the eastern U.S. and Canada, most of South America and western parts of Europe and Africa. Eastern Europe and most of Asia will miss the latter hours, while the transit will already be in progress when the sun rises in the western U.S. and parts of South America. Australia, New Zealand and Oceania won't get to see any of it.