Sky & Telescope - December 2020 - 58

ECLIPSE SCIENCE

by David Billesbach & Timothy Arkebauer

What Does
Your Lawn
Think of
a Solar
Eclipse?
This month, a total solar
eclipse will grace the skies
of Chile and Argentina.
Humans won't be the only
lifeforms that take notice.

58

DECEMBER 2 02 0 * SK Y & TELESCOPE

p GROUND CRESCENTS Eclipse chasers are familiar with the crescent
shadows that foliage can cast during the partial phases of an eclipse.
But does the foliage react to the eclipse, too?

and the vegetation, as well as how much solar energy falls on
the surface and heats the air and warms the soil. The amount
of CO2 exchanged between the atmosphere and the soil/plant
community is called the flux of CO2. Plants use energy in
the visible part of the solar spectrum to "fi x" CO2 from the
atmosphere into carbohydrates; that's the basics of photosynthesis. Typically, this process dominates the CO2 exchange in
daytime, and the value for the CO2 flux is negative - think
of it as the plants eating CO2 from the atmosphere. At night,
plant and soil respiration dominates the exchange, and the
value is positive. We reasoned that this process should be very
sensitive to the eclipse, since it's powered by sunlight.
To directly tie the CO2 flux to the eclipse, however, we
needed to also track the change in sunlight. That we did with
our radiation sensor, which measures how much solar energy
falls on every square meter of surface per second. We decided
that together, these two measurements would tell us how
plants "see" an eclipse.

M A BEL LOO MIS TODD / TOTAL ECLIPSES OF THE SUN 1894

P

eople lucky enough to have witnessed a total solar
eclipse will tell you what an awesome experience it was
and how profoundly affected they were. We humans
notice these things and attach a lot of meaning to them.
Animals are also acutely aware of solar eclipses. The rapid
darkening in the middle of a day can set them on edge. Pets
will act confused and sometimes frightened, and livestock
will often think that it's evening feeding time in the middle
of the day. Birds will start singing their evening songs.
But how do plants perceive an eclipse? What about the
elm tree in your yard or the tomatoes in your garden? Do
they notice?
During the August 21, 2017, total solar eclipse, we had a
unique opportunity to find out. We study how plant communities interact with the atmosphere, the groundwater,
and sunlight in a variety of ecosystems. One of our study
sites is located in the vast grassland known as the Nebraska
Sandhills, very near to where the annual Nebraska Star Party
is held. And, luckily for us, this site lay right in the path of
totality.
At the site, we have instruments that measure how much
CO2 and water vapor are exchanged between the atmosphere



Sky & Telescope - December 2020

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Sky & Telescope - December 2020 - 1
Sky & Telescope - December 2020 - Contents
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