Countdown to the Eclipse
What is a total solar eclipse?
Photo credit: Rick Fienberg, AAS
A total solar eclipse occurs when the New Moon comes between the Sun and Earth and casts the darkest part of its shadow, the umbra, on Earth. A full solar eclipse, known as totality, is almost as dark as night.
A Complete Solar Eclipse Has 5 Phases
There are 5 stages in a total solar eclipse:
- Partial eclipse begins (1st contact): The Moon starts becoming visible over the Sun's disk. The Sun looks as if a bite has been taken from it.
- Total eclipse begins (2nd contact): The entire disk of the Sun is covered by the Moon. Observers in the path of the Moon's umbra may be able to see Baily's beads and the diamond ring effect, just before totality.
- Totality and maximum eclipse: The Moon completely covers the disk of the Sun. Only the Sun's corona is visible. This is the most dramatic stage of a total solar eclipse. At this time, the sky goes dark, temperatures can fall, and birds and animals often go quiet. The midpoint of time of totality is known as the maximum point of the eclipse. Observers in the path of the Moon's umbra may be able to see Baily's beads and the diamond ring effect, just after totality ends.
- Total eclipse ends (3rd contact): The Moon starts moving away, and the Sun reappears.
- Partial eclipse ends (4th contact): The Moon stops overlapping the Sun's disk. The eclipse ends at this stage in this location.
The Great American Eclipse
The coming total solar eclipse of August 21, 2017 is widely called the Great American Eclipse because it will be so accessible to so many millions of Americans. A total solar eclipse is easily the most spectacular sight in nature when the sky suddenly darkens and the most beautiful object in the sky — the Sun's shimmering corona — becomes visible for two minutes or so. To see a total solar eclipse is an intensely emotional experience and a memory for a lifetime.
- The path of totality cuts a diagonal path across the nation from Oregon to South Carolina and most Americans live within a day's drive to the path of totality.
- The United States has an excellent highway system and most American families have it within their means to take a short driving vacation.
- August is an ideal month for a vacation; the weather is warm and the chance of summer storms has diminished in much of the nation.
- Most schools have not yet begun their fall session by August 21st and some schools near the path of totality are scheduling a late start.
- Social media will have a huge impact on motivating eclipse visitors. The eclipse is exactly the type of event guaranteed to go viral on Twitter, Facebook, Instagram, and other social platforms. We expect that many people will only make plans to go in the week before eclipse day.
Looking directly at the Sun is unsafe except during the brief total phase of a solar eclipse (“totality”), when the Moon entirely blocks the Sun’s bright face, which will happen only within the narrow path of totality.
The only safe way to look directly at the uneclipsed or partially eclipsed Sun is through special-purpose solar filters, such as “eclipse glasses” (example shown below) or handheld solar viewers. Homemade filters or ordinary sunglasses, even very dark ones, are not safe for looking at the Sun.