Jasper Dark Sky Festival

Eclipse 2017: Enjoying the Partial Eclipse

Even if you can’t travel to the centre line, there’s still something to see.

ECLIPSED SUN The last solar eclipse widely visible across Canada was a partial-only event on October 23, 2014. In this view, roughly 50 percent of the Sun is covered by the Moon. On August 21, some Canadians may see as much as 90 percent of the solar disc eclipsed. Courtesy Alan Dyer

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.

As this map illustrates, the closer to the path of totality you’re situated, the greater the percentage of the solar disc eclipsed by the Moon. Map Courtesy Michael Zeiler/GreatAmericanEclipse.com

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.

A 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 like the one available here.

FRONT-APERTURE FILTERS While the eclipse can be enjoyed without optical aid, the view is more exciting through a telescope. For the partial phases, you’ll need a safe solar filter that fits over the front of the telescope. Appropriate filters are available in various sizes from telescope stores in Canada and the United States. Courtesy Alan Dyer

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 his Amazing Sky web site.

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