Watch Mercury's transit across the sun (without frying your eyes)

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39576 full

Monday morning, from sunrise until around 11:40 am, there will be a tiny black dot moving across the sun.

Sure, you probably won't notice, but that silhouette is the planet Mercury making a somewhat irregular journey. The last time it crossed the sun from our perspective was 10 years ago, the next time will be the year 2019.

That's not to say Mercury won't pass by the Earth until then. It zips by us about every four months, but a transit like this only happens when Mercury orbits in direct line of our view of the sun.

The transit began around 4:12 a.m. PT but wasn't expected to be visible until sunrise at 5:56 a.m. PT.

NASA video

It'll take about seven and a half hours for the planet to make its solar journey, though in California we'll only be able to witness part of that.

Don't expect to spot it with your naked eye, either.

Without special solar filter glasses, you'll likely fry your eyes. Even if you use these super-shades, Mercury's outline will only by about 1/160th the width of the Sun's apparent size.

Sky and Telescope magazine has some handy tips for how you can safely watch the transit.

You can also watch a live feed below, if you'd rather stay inside.

Ustream

Griffith Observatory also has a live stream available but will be closed to the public during the actual event since it is typically not open on Mondays.

If you are looking for more of an experience, head up to Mount Wilson to check out the transit on various solar telescopes, including the observatory's 150-foot Solar Tower. The grounds open at 5:30 am. 

Cal State Fullerton is also inviting the public to view the event through its telescopes Monday morning, starting at 8 am. Parking is free at the Fullerton Arboretum for those looking to join the fun.

Williams College astronomer Jay Pasachoff will be watching the transit from the Big Bear Solar Observatory on an island in Big Bear Lake. He’ll be looking at a telescopic image of the event.

The transit of Mercury from November 2006 as seen from Haleakala, Hawaii.
The transit of Mercury from November 2006 as seen from Haleakala, Hawaii. Jay Pasachoff / Glenn Schneider and Suranjit Tilakawardane

He says as Mercury’s silhouette enters and exits the bright disc of the sun, its shadowy image will distort into a tear shape thanks to an optical phenomenon called the black drop effect.

When Mercury's dot enters the sun's bright circle, it appears as if a black line forms between the planet's silhouette and the blackness surrounding the sun. Pasachoff likens it to taffy being stretched between the two. After about a minute, the dark band disappears and Mercury appears as a disk inside the sun. 

It is this effect Jay Pasachoff plans to study.

"So we’re understanding what happens when objects just barely go into or out of other objects in silhouette," he explained.

It turns out, that's a hot topic these days because scientists are using transits to study exoplanets, or alien worlds orbiting distant stars. As these exoplanets cross the light we see from those stars, they make a silhouette that can tell us things about those far off worlds.

Mercury’s transit Monday can help refine techniques to study those alien worlds and gaining a better understanding of the distortion caused by the black drop effect is part of that.

This story has been updated. A previous version stated that the solar observatory shows a refracted image of the transit. It shows a reflected image. Also, language was changed to better explain the black drop effect.

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