Sky and Telescope - August 2018 - 18

Expanded Roles
for Citizen Scientists
Thanks to the relative ease of getting to the path of totality last year, citizen scientists played a key and arguably
powerful role. Some teams studied the Sun's corona and
chromosphere, while others monitored the response of
Earth's ionosphere and neutral atmosphere to the rapidly
changing incidence of sunlight.
The Citizen CATE (Continental-America Telescopic
Eclipse) project extended the idea of multiple observations to the max. A team led by Matt Penn (then at National
Solar Observatory) brought together amateurs and professionals to operate 68 nearly identical setups strung along
the eclipse path from Oregon to South Carolina (S&T: Jan.
2016, p. 29). The resulting images from 61 successful stations are being combined to yield an 82-minute-long record
of the corona's appearance and its evolution. Challenges
still remain in combining and analyzing these thousands
of images, but the end result promises to be the longest
scientific-quality observation of the solar corona in history.
Two programs studied the changes in the propagation
of radio signals just before, during, and after the eclipse.
Eclipse Mob provided radio receivers to more than 500
citizen scientists across the U.S. The volunteers monitored
special transmissions to note how radio propagation varied
across the country due to the eclipse. In the Ham Radio
Science Citizen Investigation (HamSCI), led by Nathaniel
Frissell (New Jersey Institute of Technology), investigators
and ham-radio operators studied how the Moon's shadow
created temporary "night-like" propagation conditions in the
ionosphere at multiple frequency bands.
GLOBE Observer, a NASA-led citizen science program,
enlisted the help of more than 10,000 volunteers nationwide. They used a customized smartphone app to collect
more than 20,000 cloud observations, 60,000 photos, and
80,000 air-temperature measurements that will answer the
question "How Cool Is an Eclipse?"
q The Citizen CATE Experiment deployed 68 teams with identical
telescopes and cameras all along the eclipse path. Remarkably, 61
of them obtained usable high-quality images during totality. The
view here is shown in raw (left) and enhanced versions.

18

AUGUST 2 018 * SK Y & TELESCOPE

depending on their frequency. Changes in the ionosphere
affect the propagation of radio communications and consequently can sometimes disrupt signals bounced around Earth
or sent into space. Given the huge impact this can have on
communication and navigation systems, understanding the
physics and behavior of the ionosphere is important.
As the influx of solar radiation changes between day and
night, structures and waves form throughout the ionosphere
that are constantly moving horizontally and vertically. A total
solar eclipse creates a relatively local but well-understood and
well-defined shadow across the globe. As the Sun is covered,
the decrease in ultraviolet and X-ray sunlight causes the
ionization rate to plummet and a drop in the total electron
content (TEC) in the ionosphere - an electron hole, in effect.
Researchers have studied the impact of eclipses on the
ionosphere for almost a century, but their measurements
have been sparse and often inconclusive. By contrast, 2017's
eclipse allowed for both large- and small-scale measurements,
yielding the most complete picture of the ionosphere ever
imaged. It offered us a giant controlled experiment to study
how the ionosphere changes in response to a brief but abrupt
shutting off of sunlight.
Gregory Earle (Virginia Tech) and his team used computer models to predict how the ionosphere's structure would
change, and thus how differently radio signals would propagate, in response to the eclipse's shadow. They predicted the
formation of a TEC hole and a change in the transmission
properties of the ionosphere that enabled radio signals to
travel farther. This is exactly what happened. Ham radio operators across the country were able to talk during the shadow's
coast-to-coast crossing despite being up to 4,000 km apart
- all the way from South Carolina to California. Ordinarily
that's possible only at night, whereas typical daytime distances
(depending on the frequency used) are only 100 to 1,000 km.
But the team's work also indicates that the way the ionosphere reacts when plunged into darkness depends on other
solar factors. In collaboration with colleagues at the Naval
Research Laboratory and University of Michigan, and drawing on fundamental studies of the ionosphere from previous
decades, the researchers found that how the ionosphere will
respond depends on what's going on in solar active regions
and whether the Sun has recently emitted flares.
Others also saw interesting
changes in the ionosphere. A team
led by Philip Erickson and Shunrong Zhang (MIT) modeled how the
ionosphere would respond to the
eclipse and then tested that result
with radio observations at Haystack
Observatory in Massachusetts. Their
models did well in describing ionospheric variations due to changes in
ionization as the sunlight diminished, but the resulting dynamics
proved difficult to understand. For

CITIZEN CATE E X PERIMENT 2017 TE AM

2017 Eclipse Results



Sky and Telescope - August 2018

Table of Contents for the Digital Edition of Sky and Telescope - August 2018

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