Watch Mercury move across the sun online — or in the sky, if you’re lucky and careful

Alan Boyle
A multiple-exposure image from NASA’s Solar Dynamics Observatory shows Mercury’s track across the sun’s disk in 2016. (NASA / GSFC / SDO Image / Genna Duberstein)

The planets will be aligned on Monday for a rare astronomical event known as the transit of Mercury, and skywatching fans are sure to see it even if the skies are cloudy, thanks to this little thing called the internet.

For folks in Western Washington, watching the action online will be the best bet when the tiny black dot of Mercury’s disk crosses the sun. Mercury will make its first contact at 4:35 a.m. PT, when the skies will still be dark in Seattle. It’ll be another two and a half hours before the sun creeps over the Cascades. By that time, the transit will be almost half-done.

Even then, the weather forecast calls for clouds that could well obscure the view for the rest of the transit, which ends at 10:04 a.m. PT.

Clouds won’t be a problem for NASA’s Solar Dynamics Observatory, however. From its vantage point in space, SDO will be beaming back high-resolution, multi-wavelength views of the sun with Mercury’s speck, and NASA’s Goddard Space Flight Center will be posting those views online.

Here on Earth, several video streams will be running, courtesy of the Slooh online observatory, the Griffith Observatory in Los Angeles, TimeAndDate.com, Britain’s Royal Observatory and the Virtual Telescope Project 2.0.

This chart shows the track that Mercury will follow during Monday’s transit. (NASA / JPL-Caltech Graphic)

If the heavens part in Seattle, there are ways to watch the transit happen in the sky. One sure way not to do it is to try looking directly at the sun with your unprotected eyes. That can do serious eye damage. Mercury’s speck is so small, and the atmospheric conditions are likely to be so dicey, that it’s hardly worth making the attempt even if you’re using the solar-filter glasses you saved from 2017’s eclipse.

A better bet would be to use binoculars or a telescope properly equipped with solar filters. Some of those viewing aids are custom-made with the filters, and you might be able to pick them up over the weekend at a well-equipped telescope or camera store if you’re so inclined.

There are also solar filters that fit over the front lenses of binoculars, or attach onto the barrel of a telescope. But don’t try looking at the sun through plain old binoculars or a telescope eyepiece, even if you’re wearing the eclipse glasses. The concentrated sunlight could burn right through the filter.

For an easy and sociable way to watch the transit in person, find a viewing party. Greg Scheiderer’s Seattle Astronomy blog lists several, including a gathering that he’s planning to host at Seacrest Marina Park in West Seattle at 7 a.m. PT Monday (weather permitting). Other shindigs are being set up at Pierce College in Lakewood, and at the Goldendale Observatory near the Columbia River Gorge.

NASA says the transit is a teachable moment for orbital mechanics: Even though Mercury swings around the sun every 88 days, not every passage results in a transit across the sun’s disk as seen from Earth. That’s because the orbits of the planets are tipped with respect to each other. Most times, Mercury passes above or below the sun’s disk as it crosses in front.

It’s the same for Venus, the only other planet that comes between us and the sun.

Monday marks the first transit of Mercury since 2016, but if you miss this go-around, the next viewing opportunity won’t be until 2032. And if you’re waiting for Venus to do a reprise of its widely watched 2012 solar passage, take good care of yourself: The next transit of Venus takes place in 2117.

Update for 3:15 p.m. PT Nov. 8: I originally wrote that you could try watching the transit indirectly by using a simple pinhole camera, but German science writer Daniel Fischer said Mercury would be too small to be seen with that method. It works well for solar eclipses, but not that great for seeing a tiny black fleck on a projected image of the sun. It is possible, however, to set up a projection system using binoculars, as Fischer explains in his tweets:

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