The Aug. 21 solar eclipse bids to be more than a rare celestial event — it could meld the increasingly pervasive world of smartphone apps with a total eclipse visible from sea to shining sea.

At least 15 free apps that focus on the eclipse are available for Android phones, iPhones or both. Here are three of the most noteworthy.

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ECLIPSE2017.ORG allows you to choose a location on a map of the United States to find out whether it is in the path of totality. If the spot chosen is outside the path of maximum darkness, a user can determine how much of the sun will be covered during the eclipse. (Free; compatible with iPhone, iPad and iPod touch, requires iOS 8.0 or later; Android 4.1 and up)

SMITHSONIAN MOBILE offers an eclipse countdown measured by days, weeks, hours, minutes and seconds until the big moment; a NASA eclipse live stream; the eclipse path across the United States; an interactive eclipse sky map; an interactive map showing the moon’s shadow passing over the nation; basic information about solar eclipses; and a safety guide. (Free; compatible with iPhone, iPad and iPod touch, requires iOS 8.0 or later; Android 2.3 and up)

ECLIPSEFLITE provides the most ideal airport locations to view the event. It also suggests the best locations to view the total eclipse in the United States, depending on weather that day. (Free; compatible with iPhone, iPad and iPod touch, requires iOS 9.3 or later)

— The Mercury News (TNS)