In the following excerpt from Totality – The Great America Eclipses of 2017 and 2024 – by Mark Littmann and me, Fred Espenak – we provide a handy checklist that will help you keep track of what to see, and when to look, for each of these must-see events and effects. You might even want to print this page as a handy reference for eclipse day, August 21, 2017.
First Contact – The moon begins to cover the western limb of the Sun. Remember to use safe solar filters to watch the partial phases of the eclipse.
Crescent Sun – Over a period of about an hour, the moon obscures more and more of the sun, as if eating away at a cookie. The Sun appears as a narrower and narrower crescent.
Light and Color Changes – About 15 minutes before totality, when 80% of the sun is covered, the light level begins to fall noticeably — and with increasing rapidity. The landscape takes on a metallic gray-blue hue.
Animal, Plant, and Human Behavior – As the level of sunlight falls, animals may become anxious or behave as if nightfall has come. Some plants close up. Notice how the people around you are affected.
Gathering Darkness on the Western Horizon – About 5 minutes before totality, the shadow cast by the Moon causes the western horizon to darken as if a giant but silent thunderstorm was approaching.
Temperature – As the sunlight fades, the temperature may drop perceptibly.
Shadow Bands – A minute or two before totality, ripples of light may flow across the ground and walls as Earth’s turbulent atmosphere refracts the last rays of sunlight.
Thin Crescent Sun – Only a sliver of the S\sun remains, then thinner still until . . .
Corona – Perhaps 15 seconds before totality begins, as the sun becomes the thinnest of crescents, the corona begins to emerge.
Diamond Ring Effect – As the corona emerges, the crescent sun has shrunk to a short, hairline sliver. Together they form a dazzlingly bright diamond ring. Then the brilliant diamond fades into . . .
Baily’s Beads – About 3 seconds before totality begins, the remaining crescent of sunlight breaks into a string of beads along the eastern edge of the moon. These are the last few rays of sunlight passing through deep valleys at the moon’s limb, creating the momentary effect of jewels on a necklace. Quickly, one by one, Baily’s Beads vanish behind the advancing moon as totality begins.
Shadow Approaching – While all this is happening, the moon’s dark shadow in the west has been growing. Now it rushes forward and envelops you.
Second Contact Totality Begins – The sun’s disk (photosphere) is completely covered by the moon. You can now remove your solar filters and safely look directly at the eclipse.
Prominences and the Chromosphere – For a few seconds after totality begins, the moon has not yet covered the lower atmosphere of the sun and a thin strip of the vibrant red chromosphere is visible at the sun’s eastern limb. Stretching above the chromosphere and into the corona are the vivid red prominences. A similar effect occurs along the sun’s western limb seconds before totality ends.
Corona Extent and Shape – The corona and prominences vary with each eclipse. How far (in solar diameters) does the corona extend? Is it round or is it broader at the sun’s equator? Does it have the appearance of short bristles at the poles? Look for loops, arcs, and plumes that trace solar magnetic fields.
Planets and Stars Visible – Venus and Mercury are often visible near the eclipsed sun, and other bright planets and stars may also be visible, depending on their positions and the sun’s altitude above the horizon.
Landscape Darkness and Horizon Color – Each eclipse creates its own level of darkness, depending mostly on the moon’s angular size. At the far horizon all around you, beyond the moon’s shadow, the sun is shining and the sky has twilight orange and yellow colors.
Temperature – Is it cooler still? A temperature drop of about 10°F (6°C) is typical. The temperature continues to drop until a few minutes after third contact.
Animal, Plant, and Human Reactions – What animal noises can you hear? How are other people reacting? How do you feel?
End of Totality Approaching – The western edge of the moon begins to brighten and vividly red prominences and the chromosphere appear. Totality will end in seconds.
Third Contact – One bright point of the sun’s photosphere appears along the western edge of the moon. Totality is over. The stages of the eclipse repeat themselves in the reverse order.
Baily’s Beads – The point of light becomes two, then several beads, which fuse into a thin crescent with a dazzling bright spot emerging, a farewell diamond ring.
Diamond Ring Effect and Corona – As the diamond ring brightens, the corona fades from view. Daylight returns.
Shadow Rushes Eastward
Shadow Bands Reappear – Shadow Bands may be seen during the first 1-2 minutes after totality ends.
Crescent Sun – Partial phases occur in reverse order. Once again, you must use your solar filter to watch all the partial phases of the eclipse.
Recovery of Nature Partial Phase – Flowers open up, animals return to normal behavior, daylight regains its strength.
Fourth Contact – The moon no longer covers any part of the sun. The eclipse is over.
Read much more in Totality – The Great America Eclipses of 2017 and 2024 by Mark Littmann and Fred Espenak.
Bottom line: A handy checklist of must-see events and effects during the August 21, 2017 total solar eclipse.
Fred Espenak is a scientist emeritus at Goddard Space Flight Center. For decades, he has been NASA's expert on eclipses, and some of you may know him as Mr. Eclipse. Fred maintains NASA's official eclipse web site (eclipse.gsfc.nasa.gov) as well as his personal web site on eclipse photography (mreclipse.com). Now retired and living in rural Arizona, Fred spends most clear nights losing sleep and photographing the stars (astropixels.com). His latest website is devoted to helping you enjoy eclipses (www.eclipsewise.com). He is an EarthSky content partner.