Sky and Telescope - January 2016 - 24

BIG SKY COUNTRY The surrounding mountain peaks
are cloudy, but the Snake River Plain basks in sunshine
in this view to the north from the Craters of the Moon
National Monument in Idaho - one of the sunniest
places along the eclipse path.

one: 99.6% of the Sun's disk area will be obscured. (This
corresponds to an eclipse magnitude of 0.994, the fraction
of the Sun's diameter to be covered.) Boise still makes a
good starting point for the 85-mile drive via Interstate 84
to reach the centerline.
The eclipse track crosses the Sawtooth Range and
descends onto the Snake River Plain. Although Idaho
Falls is 21 miles south of the eclipse path's central line,
it still enjoys 1¾ minutes of totality. Another 30 seconds
can be gained by traveling to the path's midpoint.
"Great" eclipse weather should be the norm for the

Two Eclipse-Planning Essentials
Authors Fred Espenak and Jay Anderson have
collaborated on many eclipse-related publications
for more than 20 years. Now retired, they've reunited
to publish Eclipse Bulletin: Total Solar Eclipse of 2017
August 21. It's ﬁlled with tables, charts, maps, weather
data, and eclipse circumstances for more than 1,000
cities in the U.S. and elsewhere. Go to eclipsewise.
com/pubs/TSE2017.html for more information.
Separately, Espenak recently published Road Atlas
for the Total Solar Eclipse of 2017, a book of detailed
road maps covering the entire path from Oregon to
South Carolina. The track is plotted in 20-second
steps, making it easy to estimate the duration of totality from any location along the eclipse path. To learn
more, visit eclipsewise.com/pubs/Atlas2017.html.
Both of these useful publications are available from
ShopatSky.com.
- J. Kelly Beatty

Januar y 2016 sky & telescope

portion of the path on the lee side of the Cascade Range.
Air ﬂowing downward into the valleys warms and dries
out, yielding the lowest average cloud cover along the
entire track. Airport statistics show that mean cloudiness drops to roughly 25% in both Oregon's Columbia
Basin and in Idaho's Snake River Plain. The percent of
possible sunshine - the best measure of the true probability of seeing the eclipse - exceeds 80%.

Wyoming and Nebraska
Next the umbra climbs over the Teton Range and enters
Grand Teton National Park in Wyoming. The grandeur
of the Tetons normally draws many thousands of visitors
each summer - adding a total solar eclipse makes the
region even more attractive as a travel destination. At
Jackson Hole's airport, which lies right on the centerline,
totality lasts 2m 20s centered on 11:36 a.m. MDT.
The shadow track crosses the Continental Divide in
the Wind River Range and descends to the high plains
of the Cowboy State. Casper is the largest Wyoming city
in the path, and the centerline passes through the south
side of the city, giving spectators a total eclipse lasting
2m 26s. (Although the longest totality will be seen 980
miles farther east in Carbondale, Illinois, Casper's duration is only 14 seconds shy of it.)
Casper is well served by highways running east and
west through the eclipse path. This gives eclipse chasers
with mobility the option to move if weather becomes an
issue. In fact, the Astronomical League has chosen Casper
to hold its annual convention just days before the eclipse
for this very reason (astrocon2017.astroleague.org).
Historical data suggest a gradual increase in cloudiness as the eclipse path moves eastward across Wyoming

JAY ANDERSON

Planning for Totality

http://www.eclipsewise.com/pubs/TSE2017.html http://www.eclipsewise.com/pubs/TSE2017.html http://www.eclipsewise.com/pubs/Atlas2017.html http://www.ShopatSky.com http://astrocon2017.astroleague.org

Sky and Telescope - January 2016

Table of Contents for the Digital Edition of Sky and Telescope - January 2016