Sky and Telescope - January 2016 - 26

Planning for Totality

Ontario, OR

77.4

6.5

16.1

Idaho Falls, ID

42.5

25.7

31.8

Eastward from St. Joseph, the protective inﬂuence of
the western mountains largely comes to an end, and you
can expect an environment that typically has a generous
supply of subtropical moisture. Along the eclipse track
through Missouri and Illinois, average afternoon cloud
cover rises steadily toward the east, increasing from
under 50% to a bit more than 60%. Yet available sunshine remains relatively constant, perhaps suggesting
lots of semitransparent overcast.
Kansas City straddles the southern limit, so the duration of totality there ranges from zero (partial eclipse
only) to more than 1 minute, depending on an observer's
exact location within the city. A similar situation is true
for St. Louis, which the eclipse path's northern limit
bisects. As the umbral track follows the Missouri River,
it crosses the St. Francois Mountains and descends to
the Mississippi and Ohio river valleys and across the Big
Muddy Watershed before entering Illinois.
Carbondale, Illinois, holds two unique distinctions.
First, the path of the 2017 eclipse has its greatest duration, 2m 40.3s, at a point about 6 miles south of the town.
Second, Carbondale also lies in the path on the next total
solar eclipse to cross the U.S., in 2024. So it's no surprise
that this small city is billing itself as the "Eclipse Crossroads of America."
Satellite data show that cloudiness decreases a lot
from morning to afternoon in Nebraska, Kansas, and
Missouri. This poses a bit of a dilemma for site selection, as the time of the eclipse is close to local noon.
Keep in mind that the arrival of the Moon's shadow will
be heralded by a drop in temperature, suggesting that
the morning curve in the graph at upper left might be
the more appropriate.
From a purely weather standpoint, the overall best sites
along this portion of the path are in western Missouri. But
Carbondale lies in the lowlands of the Ohio and Mississippi rivers, giving this community the (statistically) leastfrequent cloud cover in the eastern part of the region.

Jackson Hole/
Teton Village, WY

25.7

42.5

31.8

Kentucky, Tennessee, and Georgia

Casper, WY

25.5

36.2

38.2

Alliance, NE

32.6

32.8

34.5

Grand Island, NE

25.5

28.6

45.9

Kansas City/
Platte, MO

21.8

31.4

46.8

Omaha, 40 miles north of the track, experiences a partial
eclipse with 98.5% obscuration.

Kansas, Missouri, and Illinois
The eclipse track clips the far-northeastern corner of
Kansas and crosses the twisty Missouri River three
times while entering Missouri. The centerline runs
through St. Joseph, where totality lasts 2m 38s centered
on 1:08 p.m. CDT.

Eclipse Site Cloud Statistics

125°°

120°

115°

110°

Morning
Afternoon

105°
100°
West Longitude

95°

90°

85°

80°

UPS AND DOWNS Twenty years of satellite data have yielded these
plots of morning (blue) and afternoon (red) cloud cover along the eclipse
centerline. Use these trends for comparative purposes - not as absolute
probabilities. Go to www.eclipser.ca for more weather statistics.
Location

Clear

Few or
scattered

Broken or
overcast

Average
cloud cover

Newport, OR

18.4

15.6

65.9

Salem, OR

36.7

18.3

45.0

Redmond, OR

50.4

25.2

24.2

St Louis, MO

8.4

31.5

60.1

Nashville, TN

4.9

42.9

52.1

Anderson, SC

4.9

44.5

50.5

Charleston, SC

2.8

29.2

68.2

Data are derived from cloud-cover statistics gathered 1979-98 at weather stations (mostly
airports) nearest to the listed location. The ﬁrst three columns of values provide the likelihood
(as percentages) of speciﬁc sky condition at time of eclipse during August. The ﬁnal column
lists the average fraction of the sky (as percentages) covered by cloud at eclipse time.

Januar y 2016 sky & telescope

S&T: LEAH TISCIONE SOURCE: JAY ANDERSON

Nashville, TN

Festus, MO
Carbondale, IL

Columbia, MO

St. Joseph, MO

Grand Island, NE

Alliance, NE

Anderson, SC
Columbia, SC
Charleston, SC

Blue Ridge
Mountains

Laramie
Mountains

North Platte, NE

Casper, WY

Riverton, WY

0.2

Idaho Falls, ID
Jackson Hole, WY

0.3

Ontario, OR
Cascade, ID

0.4

Madras, OR
Mitchell, OR

Snake
Cascade Columbia
River Wind
Range
Basin
Plain River
Columbia
0.7
Range
Plateau
Sawtooth
Range
0.6
Snake
River
Plain
0.5
Newport, OR
Salem, OR

Mean Fractional Cloud Amount

0.8

As it crosses the Ohio River, the Moon's shadow enters
Kentucky. It's here that, at 1:25:31 p.m. CDT, the axis of
the lunar umbra passes closest to the center of Earth -
an instant known as greatest eclipse. The exact location is a
humble sorghum ﬁeld about 12 miles northwest of Hopkinsville, Kentucky. At that moment the Sun's altitude is
64° and the path of totality 71.3 miles wide. Although the
ground speed of the shadow is near its minimum - 1,447
mph - it's still nearly twice the speed of sound.
The duration of totality here is just 0.13 second less
than at the point of greatest duration near Carbondale,
Illinois, but that distinction seems to make a lot of diﬀerence to some communities promoting themselves as the
best place to watch the eclipse.
The truth is that any place along the eclipse track

http://www.eclipser.ca

Sky and Telescope - January 2016

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