August 2017 Night Skies
veryone in the United States, including Hawaii and Alaska, has an opportunity on August 21 to see at least part of the eclipse. In case you haven’t heard, folks within a 70-mile wide swath across the entire US will see a total solar eclipse. This is the first trans-continental solar eclipse since 1918. If you are within the path of totality, you will see the Sun completely blocked by the Moon. The closer you are to the centerline, the longer the eclipse.
But what should you expect to see?
Even the total solar eclipse starts with a partial eclipse. As the Moon begins to move in front of the sun, there will be no change in brightness. Most people probably won’t be aware that an eclipse has started. At about 20 minutes before totality, the Moon blocks about half of the Sun. The Sun takes on a crescent shape (don’t look at the Sun without your eclipse glasses. You should keep them on until totality). Sunlight begins to fade noticeably and the quality of light is different. Venus may become visible to the upper right of the Sun. Under trees with leaves, look for the projected crescent shape of the Sun. Looking west, toward the approaching shadow, clouds and or the horizon will appear to darken as if dusk is approaching.
You must wear eclipse glasses or the equivalent throughout the entire eclipse. The only excuse to remove them is during totality.
At about 5 minutes before totality, you should still have your eclipse glasses covering your eyes. The Sun is a thin sliver. It feels like a cloudy day and the sky is noticeably darker in the west. Note the sharpness of your own shadow. You may even see the wavy alternating bands of dark and light called shadow bands, especially if you’re near a light-colored surface like sand.
We’re almost there. With less than a minute to go, start expecting Baily’s Beads, blobs of light at the Moon’s edge where sunlight streaks through the Moon’s deepest valleys. Right before the last light fades from the Sun, the last sliver of light shines incredibly bright with the faint corona just visible along the entire edge of the Moon. This is the diamond ring effect and it lasts but a moment.
TOTALITY. Take off your eclipse glasses. You’ll want to. The corona, the whitish, wispy, glowing outer atmosphere of the Sun, shines as brightly as a full Moon. An arc of ruby-red chromosphere may be briefly visible and it’s possible we will be treated to a solar prominence. Light doesn’t feel like normal sunlight and the sky is in deep twilight. The Moon is black, silhouetted against the Sun. See Venus, possibly Jupiter and some of the brighter stars.
Enjoy this moment; at most just 2 minutes, 30 seconds. Earth is the only place in the entire solar system where this special sort of alignment takes place.
Remember to put your eclipse glasses back on the moment BEFORE the Sun reappears. Totality is complete but the entire process of the partial solar eclipse repeats in reverse for another 75 minutes or so.
This is the highlight of August but plenty more is going on. During the moonless nights toward the middle of the month, look for Perseids. This bright meteor shower goes on all month, peaking on August 11 and 12th. Full Moon occurs on August 7th just two weeks before the total solar eclipse. Jupiter and Saturn rule the evening sky. Mercury, Venus and Mars can be found in the morning sky.