Canada hasn’t witnessed a solar eclipse since October 23, 2014 (excluding eastern Newfoundland, which saw the tiniest nip out of the solar disc at sunrise on March 20, 2015). On August 21, that changes. All of Canada and the United States will enjoy a partial eclipse. Sure, a partial eclipse is much less spectacular than totality, but not everyone can get to the centre line.

Southern Canada and much of the United States will see a substantial portion of the Sun covered. Will the day look darker? That depends on where you’re situated. When roughly 80 percent of the solar disc is covered, daylight is sufficiently dimmed to be noticeable. Alert observers can even see a difference with less than 60 percent of the Sun eclipsed. At 90 percent, just a thin slit of sunlight remains visible and the lighting not only is greatly diminished but also begins to take on a silvery or steely appearance and shadows appear unnaturally sharp. Any small opening, such as the spaces between leaves, will project a tiny “pinhole” image of the crescent Sun onto the ground. These effects are visible to some extent from locations farther north, but in areas where only 50 to 75 percent of the Sun is covered, you might not notice much going on.

An Important Word About Safety

You must use a solar filter made specifically for the purpose of viewing a partial solar eclipse. (It’s safe to look at the Sun without a filter only during totality—when the disc of the Moon completely covers the Sun.) Never use photographic filters, sunglasses, exposed film, X-ray film, household Mylar, CDs, etc. The smoked glass your dad made for the eclipse you remember seeing as a child? Unsafe. While all these make the Sun appear somewhat dimmer, they may pass ultraviolet and infrared light, which could permanently damage your eyes. Play it safe: Use an eclipse viewer.

If you plan to use a telescope or binoculars to view the event, you’ll need a specialized filter designed to fit over the front aperture of the instrument. Never use eclipse glasses intended for naked-eye viewing in conjunction with any optical device!

Alan Dyer is a SkyNews contributing editor and world renowned astrophotographer. Many of his excellent photographs can be viewed on Amazing Sky.