The August 21st total eclipse of the Sun lasts several hours. During this period, there and many interesting events and effects to be looking for. In the following excerpt from Totality – The Great America Eclipses of 2017 and 2024, this handy checklist will help you keep track of what 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 on eclipse day.
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 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.
Totality – The Great America Eclipses of 2017 and 2024
Read much more in Totality – The Great America Eclipses of 2017 and 2024 by Mark Littmann and Fred Espenak.
About the Authors
Mark Littmann has written several popular books about astronomy. Planets Beyond: Discovering the Outer Solar System won the Science Writing Award of the American Institute of Physics. Planet Halley: Once in Lifetime (Donald K Yeomans, co-author) won the Elliott Montroll Special Award of the New York Academy of Sciences. Reviewers described The Heavens on Fire: The Great Leonid Meteor Storms as a “unique achievement,” “altogether satisfying,” and “a compelling read.”
Mark holds an endowed professorship, the Hill Chair of Excellence in Science Writing, at the University of Tennessee where he teaches three different courses in writing about science, technology, medicine, and the environment. He has helped lead expeditions to Canada, Hawaii, Bolivia, Aruba, and Turkey to observe total eclipses.
Fred Espenak is the most widely recognized name in solar eclipses. He is an astrophysicist emeritus at NASA’s Goddard Space Flight Center, where he founded and runs the NASA Eclipse Home Page, the most consulted website for eclipse information around the globe. His Five Millennium Canons of solar and lunar eclipses are seminal works for researchers, archaeologists, and historians.
Fred writes regularly on eclipses for Sky amp; Telescope and is probably the best known of all eclipse photographers. He leads expeditions for every total solar eclipse and has done so for more than 35 years. In 2003, the International Astronomical Union honored Espenak and his eclipse work by naming asteroid 14120 after him. The U. S. Postal Service recently used one of his photos on a postage stamp to commemorate the 2017 total eclipse of the Sun.
- More on the 2017 Total Solar Eclipse
- EclipseWise 2017 Eclipse Page
- Google Map of the 2017 Eclipse Path
- States in the Path of Totality:
- Totality – The Great America Eclipses of 2017 and 2024
- Books on the 2017 Eclipse
- Best Ways to View the Solar Eclipse
- Experiencing Totality
- 2017 Eclipse Stamp
- Total Solar Eclipses in the USA
- Eclipses For Beginners
- Safe Solar Eclipse Viewing
- How to Photograph a Solar Eclipse