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Transit of Mercury
A multiple-exposure photo shows Mercury as a speck making its way across the sun’s disk. (Credit: NASA)

For the first time in a decade, we Earthlings can watch the planet Mercury’s black speck pass across the sun today – even in Seattle, where the skies are partly cloudy at best.

“This is one of the very rare opportunities to see the parts of the solar system in motion,” said Stephanie Anderson, president of the Seattle Astronomical Society. “It doesn’t happen very often, so when you get an opportunity, take it.”

The event got started at 4:12 a.m. PT, when the edge of our solar system’s closest-in planet began its transit of the sun’s disk. That was before dawn for West Coasters, so Seattleites had to wait until sunrise at 5:40 a.m., when the transit was in progress.

That’s assuming you could see the sunrise. The Seattle Astronomical Society had planned to gather at Snoqualmie Point Park for a viewing party, but the weather was so cloudy that the society called off its party. Instead, the society’s website pointed people to these other potential viewing areas:

The transit is due to wind up about 11:40 a.m. PT.

The important thing about witnessing the transit is to see it safely. Gazing at the sun runs the risk of doing severe eye damage, so you’ll need to take precautions – or content yourself with watching the event online.

Mercury transits take place 13 or 14 times in the course of a century, with the most recent occurrence in 2016. Since then, the world was wowed by 2012’s transit of Venus. Unfortunately, today’s event isn’t as big, because Mercury is way smaller than Venus.

To spot the speck, you really need a telescope with at least 50x magnification, Anderson said. And that telescope will need a solar filter good enough to head off any possibility of eye damage. Such filters can be ordered online, or purchased at places like Cloud Break Optics in Ballard (where Anderson is co-owner).

There are still opportunities to see the transit online, and you won’t have to worry about eye protection. The Slooh virtual observatory and Columbus State University’s Coca-Cola Space Science Center are providing streaming video of the transit.

NASA’s Solar Dynamics Observatory is capturing pictures of the sun in several wavelengths throughout the transit, and scientists are passing them along online in near-real time. You can choose from eight perspectives. There’s likely to be pictures posted to SpaceWeather.com as well.

Scientists have learned a lot about Mercury from space probes such as NASA’s Messenger orbiter, which finished up its observations with a bang last year. That means there’s less to learn from transits. Nevertheless, astronomers are analyzing ever-so-slight shifts in sunlight, as seen at the National Solar Observatory in New Mexico, to gain new insights about Mercury’s thin exosphere.

The next transit of Mercury is due on Nov. 11, 2019 – but your sun-viewing skills are likely to get another workout well before that, when a total solar eclipse makes its way from coast to coast on Aug. 21, 2017. So even if Mercury’s brush from the sun is less than spectacular, you can regard Monday’s event as a warmup for the big show that’s coming next year.

This report was originally published on May 5 and updated with today’s activities.

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