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SYFY WIRE Bad Astronomy

The bruised Earth: Solar eclipse seen from space

By Phil Plait

[Credit: DSCOVR EPIC team / NASA Earth Observatory]

On February 26, 2017, the Moon passed directly between the Earth and Sun, creating a solar eclipse.

And not just an ordinary solar eclipse, but an annular eclipse. Roughly speaking, the Sun is about 400 times wider than the Moon, but about 400 times farther away. That means they appear to be about the same size in our sky.

But the Moon’s orbit is elliptical, so sometimes it’s closer to Earth, and sometimes farther away. If there happens to be a solar eclipse when the Moon is near apogee (the point in its orbit when it’s farthest from us), then it appears smaller than the Sun. It doesn’t cover the entire face of the Sun. So it leaves a little ring of Sun around it.

The technical term for a ring like that is an annulus, hence annular eclipse. And what does that look like? This:

Annular eclipse

Coooool. That was taken by Guillermo Abramson in a village called Facundo, in Chubut, southern Argentina. Along the top, you can see the full Sun, then the Sun partially eclipsed, then the annular eclipse seconds before maximum; the rough edge to the left is due to irregularities in the Moon’s surface: mountains, craters, and so on. The big shot underneath shows the perfect ring of fire, as it’s called: the circle of Sun left over due to the Moon’s inability to completely cover it. Abramson says he was mere meters from the eclipse’s centerline, so the ring was incredibly symmetric from his position.

He created this amazing animation of the event, too:

animation of the annular eclipse

I’ve never seen a complete annular eclipse; I’m adding that to my already lengthy list of things to see before the Sun becomes a red giant and cooks the Earth.*

As you can see in the photos, an annular eclipse still lets some sunlight through, so it doesn’t get completely dark where the Moon’s shadow falls on the Earth. But it does still darken the Earth. How much? Well, at the maximum eclipse, the Moon blocked 98.45% of the Sun, so 1.55% of the sunlight still got through. That’s still over 2000 times brighter than the full Moon —in general the Sun is over 150,000 times brighter than the Moon in the sky, so even letting through a small fraction of sunlight still means you get plenty of light.

But it does get darker, and that can be noticed. Especially from space! From there, you can get an overview of the planet and watch the Moon’s shadow sweep across the Earth. We got exactly that view from the Earth-observing DSCOVR satellite, and the resulting animation is extremely cool:

animation of solar eclipse seen from space

How about that? DSCOVR sits 1.5 million kilometers from Earth in the direction of the Sun, in a region of stable forces called the Lagrange 1 point (you can read about how this works in an article I wrote in 2016, when DSCOVR watched as a total solar eclipse moved across the face of the Earth)**.

And if you think this is cool —and you better, because it is — then just you wait. In August 2017, there will be a total solar eclipse visible from the US for the first time in decades, and I expect it will be the most observed eclipse in human history. The images we’ll see from that will be amazing just due to the sheer number of clever people who will photograph it creatively. I can’t wait! And I’ll have a lot more info on that event soon. Stay Tuned.

* Note to self: Add “watch the Sun becoming a red giant and cooking the Earth” to my list of things to see.

** Correction, March 14 at 02:30 UTC): Although I described its position correctly, I originally called it the Lagrange 2 point, when it's actually L1. The L2 point is opposite the Sun from the Earth.