The August solar eclipse: There's an app for that
For eclipse enthusiasts, amateur astronomers and those with just a passing interest in the Aug. 21 coast-to-coast solar eclipse, look no further than your web browser or smartphone to learn how to make the most of this rare and spectacular event.
Three smartphone/tablet apps stand out: Eclipse Safari (free), Solar Eclipse by Redshift ($1.99), and Smithsonian Eclipse 2017 (free). All three are available for Android and iOS.
Eclipse Safari is from the makers of Sky Safari, one of the leading astronomy programs for computers, tablets and smartphones. Sky Safari code also powers the same interactive map and planetarium view used by the Smithsonian app.
The well-engineered Eclipse Safari features a news feed from Space.com, realtime eclipse updates and will play NASA's livestream during the actual eclipse, showing realtime views from various sites across the nation.
Most useful, the app features a zoomable map of the United States, showing the eclipse path of totality, that lets the user specify a viewing location, either manually or using the phone's GPS.
Click anywhere on the map and it will show you when the eclipse begins and ends at your location, the duration of totality and even a countdown clock showing when the moon's inner shadow, or umbra, will reach you if you're in the 70-mile-wide path of totality.
If you're not in the path of totality, the app will show when a partial eclipse begins at your location, when it will reach maximum and when it will end. Everywhere in the United States, Canada, Central America and northern South America will see at least a partial solar eclipse.
The Smithsonian's app uses the same Sky Safari-driven map and sky view and includes the NASA TV livestream, along with recent images of the sun taken by NASA's Solar Dynamics Observatory satellite.
Both apps will draw the sun and moon as they will appear in the user's sky on the day of the eclipse. But the Sky Safari planetarium code, running on a remote server, draws the sky as it appears in daylight and the glare of the sun tends to drown out the moon.
In Sky Safari's desktop and pro astronomy apps, the user can "turn off" daylight, making the sun and moon much easier to see against a dark sky. That's not an option in the Sky Safari-driven smartphone apps, but it is in Redshift's Solar Eclipse.
As with Eclipse Safari, the Redshift app allows the user to pick an observing site anywhere in the United States (or use your phone's GPS to pinpoint it for you), instantly generating a table showing when the eclipse starts and stops at that location.
The interactive map is not as useful as the one in the Sky Safari-driven apps because it includes far fewer towns and cities and the dark colors of the display make the path of totality difficult to make out in zoomed-in views.
But the sky scenes showing sun and moon are clearly superior. The user can pull up a scroll bar to move time forward and backward in small increments and turn daylight on or off. The result is a much more attractive rendering, at least to this user. It's not necessary for planning purposes, but it's a huge help when it comes to visualizing the eclipse.
Another extremely useful feature of Redshift's eclipse app is its promised ability to show the weather at the user's location. The app says this feature will become active five days before the eclipse.
The web, of course, offers a wide variety of sites with useful maps, tips, viewing guides and other resources.
As one might expect, NASA has produced one of the more detailed eclipse pages on the web, highlighted by the agency's own interactive Google map of the nation that lets viewers click on any location to find out exactly when the eclipse will begin and end at that site as the moon's shadow races across the nation.
The NASA site provides detailed scientific background, a variety of useful maps, including one that shows details of major eclipse-related events across the country, a roundup of educational activities, instructions for building simple, low-cost pinhole-projection eclipse viewers and detailed safety tips.
The American Astronomical Society offers a remarkably thorough eclipse page, including many of the features of NASA's site. But the AAS also includes links to a wide variety of external pages featuring detailed weather data, state-by-state maps and useful links to various vendors selling certified solar filters, telescopes, binoculars, etc.
Acting as a central clearing house of sorts, the AAS page also provides links to a variety of weather-related pages, including the extremely useful Eclipsophile, which includes realtime weather updates and historical data for sites along the path of totality.
The AAS site also lists available software and eclipse-related apps of interest along with an extraordinarily detailed list of other eclipse-related resources. As one might expect from the nation's leading astronomical organization, the information provided on the AAS site is thorough and reliable. Not surprising given the AAS has been working on eclipse preparations for the past five years.
Like the AAS site, the Great American Eclipse page offers a remarkable variety of resources, from detailed state-by-state maps, to viewing site recommendations, links to vendor sites and a long list of other eclipse websites, including Eclipse2017 . Together, the AAS page and the Great American Eclipse page offer more than enough information to keep one occupied until the eclipse actually gets here.
Another must-see eclipse site is Fred Espenak's EclipseWise.com. Espenak, fondly known as "Mr. Eclipse," is a retired astrophysicist and author of several major works on eclipse science and predictions. His website includes basic and technical background, links to a wide variety of eclipse-related pages and his personal advice on how to photograph an eclipse.
Finally, eclipse enthusiasts should check out Xavier M. Jubier's interactive Google map, which provides critical data about a selected viewing site, including the size of the moon's shadow at that location, it's velocity, eclipse start and stop times and the duration of totality.
Jubier's site also shows maps for historical eclipses and upcoming events, including the solar eclipse that will pass across the central United States in 2024.
There are many, many more eclipse pages and many provide a similar level of detail. But the NASA and AAS sites are hard to beat.