Mercurial guest makes reservation

Smallest planet’s transit to put on show in U.S.

CAPE CANAVERAL, Fla. — Mercury is putting on a rare celestial show this week, parading across the sun in view of most of the world.

The solar system’s smallest, innermost planet will resemble a tiny black dot Monday as it passes directly between Earth and the sun. The event begins at 4:35 a.m. PST.

The entire 5½-hour event will be visible, weather permitting, in the eastern U.S. and Canada and all of Central and South America. The rest of North America, Europe and Africa will catch part of the action. Asia and Australia will miss out.

Unlike its 2016 transit, Mercury will score a near bull’s-eye this time, passing practically dead center in front of our star.

Mercury’s next transit isn’t until 2032, and North America won’t get another viewing opportunity until 2049. Earthlings get treated to just 13 or 14 Mercury transits a century.

You’ll need proper eye protection for Monday’s spectacle. Telescopes or binoculars with solar filters are recommended. There’s no harm in pulling out the eclipse glasses from the total solar eclipse across the U.S. two years ago, but it would take “exceptional vision” to spot minuscule Mercury, said NASA solar astrophysicist Alex Young.

Mercury is 3,000 miles in diameter, compared with the sun’s 864,000 miles.

During its 2012 transit of the sun, larger and closer Venus was barely detectable by Young with his solar-viewing glasses.

Venus transits are much rarer. The next one isn’t until 2117.

Mercury will cut a diagonal path left to right across the sun Monday, entering at bottom-left (around the 8-hour mark on a clock) and exiting top-right (around the 2-hour mark).

Although the trek will appear slow, Mercury will zoom across the sun at roughly 150,000 mph.

NASA will broadcast the transit as seen from the orbiting Solar Dynamics Observatory, with only a brief lag. Scientists will use the transit to finetune telescopes, especially those in space that cannot be adjusted by hand, according to Young.

It’s this kind of transit that allows scientists to discover alien worlds. Periodic, fleeting dips of starlight indicate an orbiting planet.

NASA’s Goddard Space Flight Center In this composite image, Mercury passes directly between the sun and Earth in 2016. The transit lasted over seven hours. Mercury will make another one Monday.