1
10 ? s
As a professional astronomer at NASA’s Jet Propulsion
Laboratory and a committed amateur astronomer at
home and at his California observatory, Steve Edberg has
witnessed countless celestial spectacles.
Even with this constant bombardment of new
astronomical experiences, his decades-long fondness for
eclipses has never dulled.
“My first recollection of seeing a solar eclipse is of the
total eclipse that crossed Alaska, Canada and the extreme
northeastern U.S. in July 1963,” Edberg said. “My family
was visiting Chicago at the time, and I just couldn’t
convince anyone to make the 800-mile drive to the path
of totality. Instead, I just saw the deep partial eclipse
there.”
Since that fateful day, the self-proclaimed avid eclipse
chaser has organized viewing expeditions and observed 16
total eclipses from land, sea and air; five annular eclipses;
numerous partial eclipses; and a wide variety of other
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COURTESY OF Steve Edberg
JPL’s Steve Edberg shines
a light on our favorite star
transitory events involving stars, planets and asteroids.
“The ‘action’ in the sky, the alignment and the spectacular
views attract me to these events and the others related
to total eclipses,” he said. “The only similar events with
the suspense and adrenaline rush were landings of the
space shuttle that I’ve seen at Edwards Air Force Base and
Kennedy Space Center.
In his professional capacity at JPL, Edberg has worked on
a variety of NASA projects including the Galileo mission to
Jupiter and the Cassini mission to Saturn. He has served as
Coordinator for Amateur Observations for the International
Halley Watch and was executive director of the Riverside
Telescope Conference, Inc. for 22 years. He also has been
honored by the International Astronomical Union with
the formal naming of the asteroid 1985QQ as (3672)
Stevedberg.
In this installment of 10 Questions, Edberg discusses
eclipse phenomena and solar science.
Sky ’ s
Up
No and Yes. Only Earth is treated by its natural satellite, the Moon, appearing large enough to just
cover the Sun without covering much of the sky around the Sun. Some other planets see the Sun
“over-covered” or way “under-covered” by some or all of their natural satellites. Were you to visit
any of these places to observe these events, they would look very different from a total eclipse on
Earth.
If you are interested in the differences and the details, read on. It is first helpful to learn about
eclipse and related phenomena here on Earth so you can understand what is described when
viewing the events visible on other planets.
Eclipse Types and
the View from Earth
The Moon is the only natural
satellite in the Solar System
that closely matches the
apparent size of the Sun in
the sky when viewed from the
host planet’s surface (or cloud
tops, for gas planets). So, on
average, every 1.5 years the
Moon will pass in front of the
Sun having its apparent size
just slightly larger than the
Sun. When it blocks the full
disk of the Sun, we say we are
having a total solar eclipse.
Depending on the separation
of Earth and Moon and Earth
and Sun, a total eclipse can
last as long as about 7-1/2
minutes and as short as
instantaneous, being total for
only a split second.
You usually won’t hear both
of the following two eclipse
descriptions described as
partial eclipses, but they
really are. A partial eclipse
occurs when the Sun is not
completely covered by the
Moon. This situation is more
common over time because
the Moon spends more time
farther from Earth than closer
to Earth on its elliptical orbit
each month.
Every eclipse has a partial
phase, the only difference
In this recurring feature,
Sky’s Up gives students
the opportunity to ask
10 Questions to leading
astronomers, space
explorers, scientists and
cosmologists.
o o o
The questions for
this installment were
submitted by students
at Truman Middle School
in St. Joseph, Mo.
Solar power
Can solar eclipses be seen on other planets?
Sky ’ s
Up
COURTESY OF Steve Edberg
This image shows the Sun’s in ner (“lower”) corona during the total eclipse of March
29, 2006, visible from al Saloum, Egypt. Here the Moon has completely covered the
Sun, plunging the area and sky into darkness. During this time, the silvery, gossamer
corona makes its appearance.
This image shows a partial solar eclipse
visible from La Canada High School on
October 23, 2014. The whole image
was too large for the camera sensor so
it was cropped to present part of the
crescent and the large sunspot group
together. This sunspot group is much
larger than Earth and is dark because
it is 2000C cooler than the surrounding
6000C white light layer that shines on
us daily. The silhouette of the Moon is
much blacker than the sunspots; the
sunspots are still emitting light but
not as brightly as their surroundings.
Notice the mountains and valleys
visible along the edge of the Moon’s
silhouette.
COURTESY OF Steve Edberg
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