What to Look For & When During a Total Solar Eclipse
Look for these astronomical and Earthbound phenomena during the total solar eclipse on August 21st.
On Monday August 21st, the umbra (dark center) of the Moon’s shadow will race across 12 U.S. states, giving a dramatic look at the solar corona to anyone standing inside the path of totality. Meanwhile the rest of North America, Central America, the Caribbean, and northern South America, will experience a partial eclipse.
If the sky is clear and you can get yourself inside the 70 mile-wide path of totality (check here for an interactive map and times), you're guaranteed an intense experience. The brief couple minutes of total eclipse give you the chance to witness some rare phenomena. But there are other unusual astronomical sights to watch for before and after totality, or if, like most people, you’ll be in the much wider partial-eclipse zone.
A lot happens during the different stages of a solar eclipse.
Rick Fienberg / TravelQuest International / Wilderness Travel
The entire event takes about 2 hours, 45 minutes. Here's a celestial schedule of what to look for.
First Contact
Just after first contact
Rick Fienberg / TravelQuest International / Wilderness Travel
The partial phase of the eclipse begins when the Moon’s edge first appears to touch the Sun's disk, an event known as first contact. It may take a minute or two after the exact time for you to begin to notice a slight dent in the Sun’s edge: on the Sun’s celestial-western side (to see exactly where to look for your location, use our eclipse simulator).
If you have access to a filtered telescope, look for irregularities on the Moon’s edge compared to the perfect smoothness of the Sun’s edge. You’re seeing lunar hills and valleys in profile. And are there any sunspots to be seen? If one is big enough, can you see that its central part is not black but gray when compared to the blackness of the Moon?
Even if you don’t have a telescope, you can track the Moon’s progress as it moves farther onto the Sun’s face over the next hour or so using solar eclipse safety glasses. Another fun and safe way is to hold a colander above a white sheet of paper or card: You will see crescent Suns in place of the usual small circles of light.
As the eclipse grows deep, watch for the sky to gradually turn a darker blue and the day to begin to cool.
- 10 minutes before totality
The Sun will reduce to a sliver just before totality.
Rick Fienberg / TravelQuest International / Wilderness Travel
By now the crescent Sun has dwindled to a sliver when viewed through your filter, and the daylight will be noticeably dimmer and silvery.
If there's a uniform surface around, such as sand, a white sheet, or the side of a vehicle, you may see wavy “shadow bands” in the final minute or so, as the thin slit of sunlight is refracted through the little heat waves that are always present in the Earth's atmosphere — the same ones that make stars twinkle and high-power telescopic images shimmer. Since totality is so short, though, the chance of seeing shadow bands may be less likely.
As you wait for totality, look for bright planets and stars to emerge; Venus will be brightening well to the west of the Sun and Moon. Farther to the opposite side, depending on your location, you might see Jupiter. Just to the left, very close to the Sun, you also might find the much fainter, more difficult star Regulus.
- 30 seconds before totality
In the few seconds before second contact and totality, the fast-falling twilight casts sharp shadows, and the day turns noticeably cooler. Often a breeze springs up. This is when wildlife gets confused; birds roost, mosquitoes and bats may appear, and flowers close.
The sky toward the western horizon darkens — and as that darkness sweeps toward you events take on a colossal and unstoppable feel.
- Diamond Ring #1 & Baily's beads
Keep looking through your eclipse glasses and you may see a beautiful Diamond Ring appear on the bottom-left edge of the Moon for a second or two. As it fades, take off your eclipse glasses. The corona is already coming into view. The Diamond Ring will reduce to a few beads of sunlight, shining through valleys along the Moon’s edge. These are called Baily's beads. As they contract to nothing, total eclipse begins.
A beautiful Diamond Ring (left) is the precursor to totality. Baily's Beads (right) briefly follow.
Left: Rick Fienberg / TravelQuest International / Wilderness Travel; Right: Reinhold Wittich
Second Contact: Totality
The solar corona reveals itself in full glory: a filamentary halo of fine white streaks, often overlapping. If you have binoculars you're in for a real treat; there's probably no more captivating view in binocular astronomy than a closeup of the solar corona's intricate structure. Scan the halo — but first concentrate on its bottom-left inner edge.
- Start of totality: chromosphere at bottom-left
Check for a brilliant pinky-red layer, the Sun's chromosphere, visible when the last of the Sun’s surface fades away. Look for any solar prominences — tiny, bright red spots, loops or arcs. This layer will quickly thin and disappear as the Moon advances past it.
- Mid-totality: solar corona peaks
Totality happens in an instant.
Reinhard Wittich
Astronomers will be awaiting the midway point of totality (about one minute in, depending on where you are) to most clearly see the corona’s size and shape. We’re in solar minimum — the Sun's weakest stage in its 11-year activity cycle — so the corona may appear relatively small.
And although it's hard to get your eyes away from the “hole in the sky”, turn through 360° to see how strange the sky and world now look.
- End of totality: chromosphere to top-right
A few seconds before the end of totality, the chromosphere will re-emerge from behind the top-right of the Moon: another opportunity to see prominences with binoculars (though they may also be visible to the naked eye).
- Baily's beads & Diamond Ring #2
Baily’s beads may then appear in the same area. Now is the time to put down binoculars as the beads crescendo — a second Diamond Ring. If there are wispy clouds nearby, they often go pink. Now put your eclipse glasses back on; totality has been and gone.
The second diamond ring can turn nearby clouds pink.
Rick Fienberg / TravelQuest International / Wilderness Travel
Third & Fourth Contact
With third contact achieved, look briefly through your eclipse glasses at the narrowest of crescent Suns. Now is the time to look again for any shadow bands, and to once again project the crescent Sun as the partial eclipse recedes until fourth contact, when the Moon departs from the Sun's disk, as if nothing had ever happened.
Observers will be left with only one question: when is the next eclipse?
The post What to Look For & When During a Total Solar Eclipse appeared first on Sky & Telescope.
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PUBLISHED; August 02, 2017 at 03:34AM
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