How is the June 10 Eclipse Different from Others?

On Thursday, June 10, 2021, there will be an annular eclipse of the sun.

What does that mean, and what is the difference between an “annular eclipse” and a “total eclipse”?

During this eclipse, the moon will have just passed its farthest point from Earth during its orbit – what is called the apogee – so, like farther objects, it will appear smaller than usual. During a total eclipse, the moon is close enough to completely block out the sun, whereas during an annular eclipse, we see the sun as a brilliant ring of fiery light around the silhouetted disk of the moon. That ring is called an “annulus,” hence the term “annular.”

The complete ring will be viewable from very few places on Earth – mostly from central Canada. For the rest of us who can see the eclipse (depending where we are in the world), it will be the far less uncommon, partial eclipse. Even if you can’t see it directly from where you are, you can count on many thousands of photographs being published and shared all around the world for the days following this exciting celestial event.

Why does this happen? Why is the moon sometimes closer to or farther from the Earth?

To picture the shape of most orbits – the gravity path a smaller object follows around a more massive one, like the moon around the Earth – imagine cutting the open end of an ice cream cone at an angle. The shape of an orbit reflects the relationship between the force of gravity and the orbiting object’s natural disposition to move in a straight line. This is the “principle of inertia” at work: An object in motion continues in a straight line at a constant speed unless acted upon by another force – and the force in this case is the gravity relationship between the moon and the Earth. If the forces match exactly, then the orbit is circular, but this is extremely unlikely. An ellipse is a flat shape defined by two focal points, and our two orbit forces rarely match. The fact that sometimes we have total eclipses and at other times annular eclipses is a reminder the moon follows an elliptical path around the Earth rather than a circular one.

This eclipse will allow only one-tenth of normal levels of sunlight, which will make it no darker than an overcast day. But the coloring of the light will be unearthly, probably unlike anything viewers have ever seen before. Still, be careful! Looking directly at the sun can harm your eyes.

Written by Daniel Kany

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