The solar crescents show how much Sun will be covered at maximum for various locations across the U.S. and Canada during the October 23rd (Thursday) partial solar eclipse. Credit: Jay Anderson
Doing anything Thursday afternoon? Have a few minutes to spareThere’s a partial eclipse of the Sun visible across much of North America and of Mexico you might like to catch. For observers in the U.S. and Canadian West the whole event begins and ends in the afternoon before sunset. Those living east of the Great Plains will see the Sun set while still in eclipse.
During a solar eclipse, the orbiting Moon passes between the Sun and Earth, completely blocking the Sun from view as shown here. In Thursday’s eclipse, the moon will pass a little north of a line connecting the three orbs, leaving a portion of the Sun uncovered. To view a partial solar eclipse, a safe solar filter is necessary. Credit: Wikipedia
Solar eclipses occur when the Moon glides between the Earth and the Sun, temporarily blocking it from view. Total solar eclipses get most of the attention because the Earth- Moon-Sun alignment is perfect. Like a snug lid on a pot, the Moon blanks out the Sun completely to create a dramatic spectacle of a black, fire-rimmed disk set in a plush solar corona.
Partial eclipses happen because the Moon’s orbit is tipped a few degrees to the Sun-Earth line. Most months, it passes north or south of the Sun and misses it completely. But during a partial eclipse, the Moon’s close enough to that line to partially block the Sun from view. Unlike a total eclipse, all phases of a partial eclipse are unsafe to view unless you use a safe solar filter or view it indirectly via projection.
Map showing times and percentage of the Sun covered during Thursday’s partial solar eclipse. Times are Pacific Daylight – add 1 hour for MDT, 2 hours for CDT and 3 hours for EDT. Interpolate between the lines to find your approximate viewing time. The arc marked A shows where the eclipse begins at sunset; B = Maximum eclipse at sunset and C = Eclipse ends at sunset. Credit: NASA, F. Espenak,with additions by Bob King
As you can see from the map, nowhere will this eclipse be total. Maximum coverage will happen in Nunavut Territory in northern Canada where the musk oxen might catch sight of a fat solar crescent 81% covered by the moon at sunset. The farther north you live in the U.S. or Canada, the deeper the eclipse. Northern U.S. states will see around 60% covered compared to 40% in the deep south.
In Duluth, Minn. for example, the eclipse begins at 4:21 p.m., reaches a maximum of about 65% at 5:33 p.m. and continues into sunset at 6:06 p.m. Since the sun will be low in the western sky from many locations, be sure to get a spot with a wide open view in that direction.To find out times and coverage for your city, use these links:
* U.S. Cities
* Cities in Canada and Mexico
Some of the different kinds of safe solar filters available. They work by reflecting or absorbing most of the light from the Sun, allowing only a fraction through to the eyes. NEVER LOOK DIRECTLY AT THE SUN without one. Click photos for a supplier of eclipse glasses. Credit: Bob King
Solar filters come in a variety of styles from inexpensive eclipse glasses that use an optical polymer to glass welder’s filters to caps you place over the front end of a telescope. It’s important to use the correct kind – don’t stack a bunch of sunglasses and figure “it’ll do” or look through smoked glass. They still allow dangerous UV and infrared light to pass through and will mess up your retinas for life.
Because we’re on the heels of the eclipse, if you don’t already have a pair of eclipse glasses I recommend a #14 welder’s glass. It’s my favorite actually because it’s easy to stuff in a pocket and heavy-duty enough to take a few dings. You can pick one up for a few dollars at a welding supply shop. Only buy a #14 – lower numbers won’t cut it.
A piece of aluminum foil, a pin and a cardboard box are all you need to build a pinhole projector. The tiny hole creates a small image of the eclipsed Sun inside the darkened box which you place over your head. Remember to look at the projection of the sun on the inner wall of the box – not through the pinhole itself.
Projection provides a fine alternative to using a filter. You can mount a pair of binoculars (or small telescope) on a tripod and project the Sun’s image on a sheet of white paper or build your own pinhole projector using the instructions above.
You can mount binoculars on a tripod, cover one lens with a lenscap and project the sun’s image safely onto a sheet of white cardboard. Credit: Bob King
If leaves still cling to your trees this season, the narrow spaces between the leaves act like natural pinholes and will cast multiple images of the eclipsed Sun on the ground below.
You can even place one hand atop the other and let the sun shine through the gaps between your fingers to see the eclipse. Low tech as it gets, but works in a pinch.
Here are some other things to watch for during the eclipse:
* If you live where half or more of the sun will be covered, you may notice a change in the quality of daylight. To my eye, the light becomes “grayer”. What do you see?
* Telescope users will see the mountains and crater rims along the moon’s edge as tiny bumps and projections against the brilliant solar photosphere. You’ll also notice how much blacker moon is compared to sunspots. Guess what? We’ve got a huge sunspot out there right now – Region 2192. Perfect for comparison!
Partially eclipsed sun just before sunset seen from Island Lake north of Duluth in May 2012. Credit: Bob King
* Those living where parts of the eclipse happen at sunset will get an extra special view of the sun with a big bite out of it right sitting atop the southwestern horizon.
I wish you excellent weather – good luck!