Spectators in western North America are positioned perfectly to view the upcoming partial solar eclipse.
On the afternoon of October 23rd, two weeks after the Moon passes through Earth’s shadow, the Moon will cast some of its own shadow onto Earth.
Nowhere will this eclipse of the Sun be total. But as the map below shows, for most of Canada, the United States, and Mexico, the Sun will be partially eclipsed. For this event, the farther west and north you are the better. In the American West the entire eclipse happens while the Sun is still fairly high in the afternoon sky. In most of the eastern half of the U.S. and Canada, the eclipse is still in progress at sunset — offering dramatic photo opportunities if you can find a low western horizon. Along a line from the Florida Panhandle through Michigan, the Sun sets right when the eclipse reaches its maximum depth.
East of that line, the Sun will set after the partial eclipse begins but before it reaches maximum. New England misses out altogether.
The farther north you are, the deeper the partial eclipse will become. In San Diego, for instance, the Moon’s silhouette will reach 43% of the way across the Sun’s disk at mid-eclipse (3:32 p.m. Pacific Daylight Time). In Vancouver the silhouette will extend 66% of the way across (at 2:57 p.m. PDT). For precise local times for many cities and towns, and much else, see the NASA Eclipse Site.
This partial eclipse is just a warm-up. America’s next total eclipse of the Sun is now only three years away, on August 21, 2017. On that day the dark center of the Moon’s shadow will draw a narrow line from Oregon to South Carolina. See Contributing Editor Kelly Beatty's advance coverage of the 2017 eclipse for more details.
Safely Viewing an Eclipse
Do not, at any time, look directly at the Sun. You might be tempted, but even a partially eclipsed Sun can cause permanent eye damage. Be the smart one here. Don’t stack multiple pairs of sunglasses on your head and think you’re good!
Some ideas for safe viewing:
The simplest safe way to view a partial solar eclipse is to project an image of the Sun onto a piece of paper. Poke a small hole in an index card with a pencil point, face it toward the Sun, and hold a second card three or four feet behind it in its shadow. The hole will project a small image of the Sun's disk onto the lower card. This image will go through all the phases of the eclipse, just as the real Sun does. Experiment with different size holes. A large hole makes the image bright but fuzzy; a small hole makes it dim but sharp.
For a better view, you can reduce the amount of daylight shining on the viewing card by enclosing it in a long box (as shown in the image to the right). This lets you use a small pinhole, producing a sharp image.
A much better way to do pinhole projection can be arranged at a window indoors. Find a room with a Sun-facing window, turn out any lights, and pull the shades. Arrange for sunlight to enter through a small hole punched in a card near the top of the window. Set up a white piece of paper across the room to catch the Sun's image. Again, experiment with different size holes to get the best, sharpest view. (Of course, don't look through the hole directly at the Sun! Look only at the spot of light that falls on the paper.)
If the Sun is too high in the sky for this, you can direct its image horizontally into the room by setting up a small, high-quality mirror on the sill of an open window. Hold the mirror in place with modeling clay. Tape your card with the hole right onto the mirror.
Even at its best, pinhole projection gives only a small image. The throw distance in feet, divided by 9, gives the image diameter in inches. Pretty small!
Telescope or Binocular Projection
This is our Observing Editor’s favorite viewing method! You can see a much sharper and larger Sun image by projection through a small telescope or binoculars. To aim the instrument safely, look at its shadow on a white card as you swing the tube or binoculars around. (Don't use your finderscope — make sure it's capped at the front end or removed completely.)
When the instrument's shadow nears its minimum size, a brilliant beam of sunlight will burst out of the eyepiece and fall onto the card. Turn the focus knob and experiment with the card's distance behind the eyepiece until the Sun's disk is sharp and as big as you want. Bock the sunlight at the edges of your instrument with a piece of re-purposed cardboard to produce a more visible projection.
Stop by your local welding supply shop and buy some rectangular #13 or #14 arc-welder's glass. Don't get a lower-numbered shade; the Sun will be too bright to look at safely. Alternatively, you can purchase inexpensive “eclipse glasses” made from safe solar filter materials.
Read more on our solar filter safety page.
The clearest and best views of the Sun are had through a properly filtered telescope. We’ve reviewed commercial solar filters designed for telescopes several times over the years (see “Solar Filters: Which is Best?” S&T, July 1999, page 63; “Baader AstroSolar Safety Film: A New Standard in Soar Filters,” S&T September 2000, page 63; “White-Light Solar Filters” S&T Feb 2005, page 102).
Make sure the filter is secured over the telescope's front. Double-check — it’s essential to keep most of the Sun's light and heat out of the instrument. Never use a Sun filter at the eye end, where it could crack or melt in the concentrated heat.
Direct viewing with a telescope and proper solar filter gives the best views of sunspots and the complex details within them, as well as the progress of the Moon's jagged, mountainous edge making its way across the solar disk.
Remember: it’s all fun and games until someone looks directly at the Sun without proper eye protection. Use a solar filter!
Want to keep an eye on future observing events? Check out the 2015 Sky & Telescope Observing Wall Calendar!