On August 21, 2017, a total eclipse of the Sun is visible from within a narrow corridor that traverses the United States of America. The path of the Moon's umbral shadow begins in northern Pacific and crosses the USA from west to east through parts of the following states: Oregon, Idaho, Wyoming, Nebraska, Kansas, Missouri, Illinois, Kentucky, Tennessee, North Carolina, Georgia, and South Carolina (a tiny corner of Montana and Iowa are also in the path). A partial eclipse visible from a much larger region covering all of North America including the greater Lexington area.
A few minutes after entering Illinois, the shadow leaves the state as it crosses the Ohio River and arrives in Kentucky. It is here that the lunar shadow's axis makes its closest approach to Earth's center - the instant of greatest eclipse - at 18:25:32 UT1 (13:25:32 CDT). At this location (lat. = 36°58.0'N, long. = 087°40.3'W), totality lasts 2 minutes 40.1 seconds, the path width is 115 km (71 mi), the umbral velocity is 0.647 km/s (1447 mi/hr) and the Sun's altitude is 64°.
Hopkinsville (pop. 3,000) lies on the central line only 19 km (12 mi) southeast of greatest eclipse. The duration of totality here is within 0.1 second of the value of greatest duration near Carbondale, IL. Although some people are fixated on fractions of a second and the ultimate duration of totality in selecting an eclipse viewing site, these issues will fade into the noise as cloud avoidance and clear skies ascend to the rank of utmost importance on eclipse day. No doubt, a 30-second eclipse in a clear sky beats a 7-minute eclipse behind clouds.
Ever since its Oregon landfall 71 minutes earlier, the eclipse track has been gradually curving further and further south of east. Its azimuth is 115° as it crosses into Tennessee and the umbra begins the final 20 minutes of its trek through the USA.
Safe Eclipse Viewing - Every total eclipse of the Sun begins and ends with a partial eclipse. The partial phases require either a projection technique or a special solar filter to be viewed safely. Of course, during the few brief minutes of Totality when the Sun's disk is completely covered by the Moon, it is then safe to look directly at the Sun with the naked eye or through a telescope or binoculars.
Weather Prospects in Kentucky - It is early afternoon - around 1:30 pm - when the track reaches Kentucky and afternoon clouds, if there are any, will be building in the sky. Afternoons in Kentucky and much of Tennessee are no cloudier than the early morning according to observations from the weather satellites. What changes is the type of cloud: convective clouds build in the afternoon as the ground heats and warm thermals begin to rise. In contrast to eclipse sites in western states, the cloudiness measured in states east of the Mississippi shows a higher frequency of overcast conditions - just short of 20% of recordings in much of Tennessee and Kentucky. Compare this to just 10% to 15% in Wyoming and to 5% to 10% on the Columbia Plateau in Oregon.
The terrain across western Kentucky is relatively flat - a landscape of small, rolling hills that make up the Pennyroyal (Pennyrile) Plateau. Off the Interstates, roads are tree lined, limiting the view, but accompanied by generous openings that look across the many farms in the region. As the track enters Tennessee, the land begins to rise, crossing the low hills of the Highland Rim before dropping into the Nashville Basin.
A great source of weather forecasts in the days leading up to the eclipse is Jay Anderson's Eclipsophile.com.