Text: Laura Wright | Editing: Andre Mayer
CBC News Interactives
For a few spectacular moments on Monday, Aug. 21, nature will hold its breath: the skies will darken, winds will calm, the temperature will drop and birds will go quiet. The reason? A total solar eclipse. Here’s what you need to know about this rare astronomical event.
A solar eclipse happens when the moon passes between the Earth and the sun, covering the sun and casting a shadow on Earth.
The umbra is the moon’s shadow that is cast on Earth. Any region that falls within the umbra’s path — known as the path of totality — will experience a total eclipse.
The penumbra is the region on Earth that is partially darkened by the moon’s shadow. Any region within the moon’s penumbra will experience a partial eclipse.
A total solar eclipse is only possible because of a coincidence.
The sun’s diameter is 400 times wider than the moon’s, but the sun also happens to be 400 times farther away.
So, from our perspective down on Earth, the sun and moon appear to be the same size during a total solar eclipse — which is why the sun gets completely blocked by the moon.
The path of totality, the region which will get a total eclipse, stretches across the U.S. from the northwest to the southeast. About 12 million people live directly along this path, and another 200 million are within a day’s drive (including many Canadians).
Those in the penumbra are still likely to be treated to a partial eclipse (weather permitting). The penumbra is wide, stretching north to Canada, and south to Central America and parts of South America.
There are partial eclipses every year — that’s when the alignment of the moon is slightly off and does not fully obstruct the sun.
Total solar eclipses are more rare. They happen about once every year and a half, but since the moon’s shadow is relatively small, not many people get to see them. There hasn’t been a total solar eclipse across the entire U.S. since 1918.
While fascinating to witness, it’s dangerous to look directly at an eclipse without proper protective eyewear.
Looking at the sun anytime can be damaging because it outputs more energy than our eyes can handle. But in the event of an eclipse, the effect can be even more intense.
When it’s dark, our pupils dilate to take in more light. If you were to look at the sun immediately after an eclipse, when the sun came back into view, your widened pupils would become flooded with bright light, which can cause serious damage — it only takes a second.
It’s only safe to look at the sun during totality, which will last two minutes and 40 seconds on Aug. 21. Be sure to check exact times of totality if you’re lucky enough to be in the path.
To protect your eyes, wear special eclipse glasses, which you can get at many local museums and science centres, or order through websites like the Royal Astronomical Society of Canada. NASA says to make sure the glasses have certification information, with a designated ISO 12312-2 international standard. Don’t use them if they’re bent, damaged or more than three years old.
NASA’s Jet Propulsion Laboratory also has instructions for making a pinhole eclipse viewer.
If you’re viewing through a telescope or taking pictures, make sure to get special lenses for those, too.
Disclaimer: The images and animations in this feature are not to scale, and some images differ from what you may see on the day of the eclipse.