Beyond Totality: Appreciating the Partial Eclipse

Posted on Thu, August 17, 2017

A partial eclipse.

Partial eclipse on May 31, 2011. Credit: Rhys Jones/WikiCommons

Here we are, less than one week until a total solar eclipse crosses the United States. For the past three years, my excitement has been building, and all of my eclipse-chaser friends have been saying, “You HAVE to go see totality!” The path of totality (the narrow region where the Sun will appear totally blocked) is relatively convenient for North Americans, but many people won’t be able to travel and witness the total phase of the eclipse.

If you can’t be “in the path” on August 21, don’t lose heart! You can still see the eclipse from outside that limited region. The partial phases of the eclipse (when the Moon only partially blocks the Sun) will be visible over a huge area, from Greenland to Brazil and from Hawaii to Cape Verde. Here are some reasons why your partial eclipse experience will be awesome.

1. Duration

The partial phase of the eclipse takes quite a while, up to three hours, as the Moon crosses in front of the Sun. For comparison, the total phase of this eclipse will only last about two minutes. So during the partial eclipse, you have more time to go outside, wait for a break in the clouds, and check out the shape of the Sun using any of these safe viewing methods. You can find out when the eclipse is happening at your location here; scroll down to see the data or an animation. Those observers in the path of totality will also experience a partial eclipse leading up to totality, and afterwards as well.

2. Motion

For me, one of the most amazing things about an eclipse is also one of the simplest: we can watch the Moon moving! We’re used to seeing the Moon and Sun rise in the east, cross the sky, and set in the west. But during an eclipse, with the Sun as a reference point, suddenly we notice the Moon creeping along as it gradually passes in front of the Sun. The motion that we’re seeing is the Moon traveling around the Earth in its orbit!

The Moon appears to move about the distance of its own diameter through the sky every hour. That seems slow, until you realize it’s actually speeding through space at 1 km per second (or 2,290 miles per hour). The best way to notice this motion during the partial eclipse is to observe the shape of the Sun (using a safe method!) every 15 minutes, and compare it to how it appeared the last time you looked. If you’re using a method that projects onto paper, you can even trace the shape of the Sun onto the paper each time to create your own record of the Moon’s motion.

A fuzzy picture of what the eclipse looks like through safe eclipse glasses.

The partial eclipse on May 20, 2012 photographed through eclipse glasses. Courtesy: Exploratorium

3. Pictures

Photographing the Sun during the total phase of an eclipse is complicated, and it requires special equipment and knowledge. On the other hand, a partial eclipse shows up nicely in eclipse glasses or as a pinhole projection. You can take pictures of the partial eclipse with a smartphone or small point-and-shoot camera via one of those two safe viewing methods. NOTE: Eclipse glasses are NOT safe to use with a telescope, binoculars, or fancy camera! They are only meant to protect your eyes. A smartphone photo taken through eclipse glasses is okay, because the camera is small enough to be completely covered by the filter. But be very careful. Your camera won’t fare well if it’s exposed to direct sunlight. You can safely (and easily) get interesting pictures of eclipse projections, whether through a specific eclipse viewer or in the shadow patterns under a leafy tree.

As a final note, the excitement about this eclipse won’t fade for long, because there will be another one visible from North America just seven years from now! On Monday, April 8, 2024, another total solar eclipse will cross the continent from Mexico to Maine. You’ll get to see all the same cool things during the partial phases of that eclipse (plus totality, if you start planning now!).

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