Sky & Telescope - April 2023 - 4

SPECTRUM by Peter Tyson
A Tangible Darkness
WHEN WE THINK total solar eclipse, our first thought might well be
of the spectacular light effects - of the Sun's ethereal corona or
Baily's Beads. But as anyone who has experienced totality knows,
the dark effects can be equally thrilling. Up there, it's all about
radiance; down here, it's all about shadow.
As totality approaches, you begin to see the western sky darken - the
umbral manifestations have begun. (Umbra comes from the Latin for shade.)
Within minutes of total eclipse, the darkness in the west begins to resemble an
approaching thunderstorm. If you're fortunate enough to be on high ground,
you can watch the Moon's shadow race toward you across lower elevations. In
her 1894 book Total Eclipses of the Sun, Mabel Loomis Todd lyrically describes
this rapidly ballooning specter as " a tangible darkness advancing almost like a
wall, swift as imagination, silent as doom. "
Meanwhile, the light around you has begun to dim and
The Moon in shadow
during the 2017
total solar eclipse
take on a surreal, slate-gray tint. As the crescent Sun thins,
its light throws ever-sharper shadows on the ground. If
you're near a white building or other suitable surface, you
might also detect one of an eclipse's more fleeting phenomena:
shadow bands. Resembling sunlight rippling on the
bottom of a swimming pool, the undulating bands appear
briefly just before and just after totality.
Not surprisingly, the most obvious shadowing effects
occur during totality, when the Moon completely blocks the Sun. The landscape
dips into twilight. It might be mid-day for you, but it feels like dusk. The
temperature drops precipitately, baffled birds head to roost, and crickets start
to chirp. Glancing up at the now-hidden Sun, you see the ultimate shadow: the
face of the Moon. It appears black as coal, and its temporary vanquishing of
sunlight has brought nearby bright stars and planets into view.
Dedicated eclipse chasers, or umbraphiles, might have a certain feature of
total eclipses that they most look forward to. For many it's the supernally beautiful
corona with its lustrous, mother-of-pearl streamers. Others might favor
red-tinged prominences or hope to see shadow bands for the first time.
But all would likely agree that what makes a total solar eclipse " the most
stunning and awe-inspiring naked-eye event in all astronomy " - as Fred Espenak
and Jay Anderson write in their cover story on page 26 - is the full package
of light and dark effects. (See them also in Bob King's column on page 48 and
Sean Walker's photo essay on page 60.) The synergy can leave viewers in tears.
In one year's time, on April 8, 2024, the second total
solar eclipse to cross the U.S. in seven years will transpire.
Are your plans in place?
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Sky & Telescope - April 2023

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