Daniel Zantzinger Skywatcher's Guide

Among the myriad celestial sights these August nights, the new moon's eclipse of the sun on Aug. 21 is clearly this month's highlight.

In a nutshell, the moon passes between earth and sun Aug. 21 (a Monday), casting its shadow called the umbra onto the earth's surface and briefly blocking sunlight. The path of the nation's first total solar eclipse in 38 years is a 70-mile wide band that stretches 8,600 miles from sunrise near Midway Atoll and the International Date Line in the middle of the Pacific Ocean to sunset southwest of the Cabo Verde archipelago in the far eastern Atlantic Ocean. For North America, the path of totality, tilted from the northwest to the southeast, is a narrow strip spanning from the westernmost coast of central Oregon to the easternmost coast of central South Carolina.

Most skywatchers, however, don't live along this path, and as such have two options.

First option is to visit https://is.gd/2017eclipsemap, find a location closest to you and hit the road. Skywatchers can book a room in Casper, Wyo., or pitch a tent in Grand Island KOA Journey campground in Nebraska.

The truly hardcore and well-financed who want to experience the greatest duration of totality need head no further than to the wilds of Giant City State Park, about six miles from Carbondale, Ill. If you want to experience the greatest eclipse, that is, be exactly where the axis of the moon's shadow slices closest to the earth's center, trek to the northwestern outskirts of Hopkinsville, Ky.

Before you pack up the RV, though, be forewarned. Totality along thiseclipse path is never longer than 2 minutes 40.2 seconds. The umbra is racing across the earth's face at three times the speed of sound, so unless you're in the unlikely position of piloting a Lockheed SR-71 Blackbird roaring down the path of totality, you're going to get your two-plus minutes as a maximum regardless where you go and how much you spend.

Second, and better, option is to stay put with family and friends. Be here now.

Although totality will come and go for the lucky few in just a few minutes, the partial eclipse lasts nearly three hours. Obscuration of the sun for the northern half of Colorado is more than 90 percent. Further, the partial for most of the rest of the country is better than 80 percent.

For skywatchers in Longmont and surrounding areas, the eclipse begins at 10:23 a.m., reaching a maximum obscuration of 93.84 percent at 11:46 a.m. before sliding off and finally ending at 1:14 p.m.

If you can, take the day off work, invite family and friends over, fire up the barbecue and make a summer day of it.

There are basically two ways that skywatchers can experience the solar eclipse, by direct viewing through a safe solar filter and indirectly by projection. It goes without saying that immensely painful and irreversible blindness can happen in an instant if you don't properly protect your eyes from the brilliance of the sun, especially when using a telescope and binoculars.

Direct viewing requires nothing more than inexpensive eclipse glasses with "ISO 12312-2" printed on them. There are pre-mounted glass and thin, metal coated plastic film filters available for telescopes and binoculars that you can buy, or you can make one yourself using Baader Astro-Solar thin film. Let it stay slack, otherwise your view will be hazy and it might tear during observation, creating dangerous viewing condition. Be sure that it can't blow off.

Projection works with a telescope, binoculars or even your hands.

Position the 3-inch or smaller telescope's aperture so the light floods through your lowest power eyepiece, and then focus the image on a mounted piece of paper. Larger telescopes risk overheating, so for those cut a 3-inchhole in a piece of cardboard and mount it over the aperture.

You can also project with binoculars. Move the paper and/or the binoculars to resolve the image.

Fold your fingers of both hands in a waffle pattern and let the sunlight through onto a flat uniform background a sidewalk, for example. You'll see multiple images of the partially obscured solar disc.

For more information, visit http://www.skyandtelescope.com/2017-eclipse.

The moon is full at 12:11 p.m. Aug. 7, and is called the Full Sturgeon Moon.

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Astronomy: August's solar eclipse nearly total - Longmont Times-Call