Observations from
Earth have fueled
Mars exploration
By DR. DANIEL BARTH
Guest Contributor
Mars is one of the five planets that you can see without
any telescope or binocular to aid you. Because Mars is
also the next planet out from Earth in our solar system,
its distance from Earth changes dramatically during each
Martian year.
As you can see from the diagram above, the orbit of
Mars brings it close to Earth once each Martian year
– about every 25 months for us – we call this Mars at
opposition because it is on the opposite side of the Earth
from the Sun. During this time, we observers on Earth
have many advantages, mostly because with Mars five
times closer Mars will appear five times larger in our
telescopes making all the fascinating surface features
easier to see.
The orbit diagram also shows us something else: Mars’
orbit is more elliptical than the Earth’s orbit. This more
elliptical orbit means that every 15 years or so, Mars
comes particularly close to us during opposition, making
telescope observation of Mars even more exciting! The
2018 summer opposition of Mars will be one of these
exceptional times when Mars is less than 50 million miles
away!
Astronomers have been exploring Mars with telescopes
for 400 years. Galileo observed Mars with his telescope
in the early 1600s. Dutch astronomer Christiaan Huygens
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Italian astronomer Giovanni Schiaparelli created this map of the surface
of Mars after observing the planet during its opposition in 1877.
made the first sketch of Mars
viewing through a 6-inch
reflecting telescope in 1659,
describing Mars’ polar cap
and timing the rotation of
Mars to 24 hours. As you can
see in the image to the right,
Huygen’s drawing of Mars
was far from precise — you
could likely do better with a
modern telescope!
Things really improved with the invention of the
achromatic or ‘color-free’ lens by Frederic Fraunhoffer
in 1812; this is a double lens than eliminates color halos
and makes our views of the planets sharp and clear. Using
Fraunhoffer’s new telescope design, Mars exploration
really heated up during the Great Opposition of Mars
in 1877. Just like 2018, the opposition of 1877 was a
particularly close approach between the Red Planet and
Earth.
Italian astronomer Giovanni Schiaparelli observed Mars
and saw what he described as canali (Italian for ‘grooves’
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or ‘channels’.) Schiaparelli was the
first to map the surface of Mars;
he noted that these ‘linear features’
must be more than 100 kilometers
wide, and thousands of kilometers
long — far enough to stretch from
the polar regions of Mars down to its
equator. Schiaparelli speculated that
these canali could be like arroyos in
our earthly deserts, shallow channels
where water occasionally flows,
and plant life is more common.
According to Schiaparelli: “Mars is a
small version of Earth with seas, an
atmosphere, clouds and winds, and
polar caps; and it promises, in this
regard, a good deal more.”
Although Schiaparelli was very
careful in his writing to explain that
it was difficult to interpret what we
saw looking through the telescope in
earthly terms, the idea of giant canals
carrying water (and life!) from the
Martian poles down to the equator
took hold of the popular imagination,
and that of scientists and astronomers
as well. This led to the Dying Planet
hypothesis.
Under the Dying Planet model,
Mars was thought to be a world
that was slowly drying out. Further
telescope exploration had shown that
the Martian atmosphere was very
thin, it might contain traces of water
and oxygen, but these elements so
essential to life were very scarce
on the red planet. The giant canali
discovered by Schiaparelli and others
were seen as evidence supporting the
dying planet model.
In 1894, American aristocrat
Percival Lowell decided to build
the world’s greatest observatory
and dedicate it to the study of Mars.
Lowell purchased a mountaintop
outside of Flagstaff, Ariz., renamed
it Mars Hill and then commissioned
a 24-inch refractor telescope (then
the largest such telescope in the
world) to be built and installed there
for his personal use. Lowell had
studied mathematics at Harvard and
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Percival Lowell observes through the 24-inch refracting telescope at the Lowell Observatory, which
he established in Flagstaff, Ariz.
traveled extensively in Asia as a
writer and diplomat, but he had no
formal scientific training. The idea
that the best observatory in the world
was owned by a wealthy amateur
astronomer for his own use must have
been more than a little irksome to the
scientific community of the day.
Percival Lowell was not only a
talented observer and artist, he was
also a gifted writer who fired the
popular imagination with his books
on Mars, illustrated by his own
sketches made at the eyepiece of his
giant telescope. In fact, his books on
Mars made him far wealthier, and
far better known, than his family’s
wealth or social position ever had.
Lowell went on to observe and
document seasonal color changes
on Mars, which he attributed to
vegetation, much as trees green up
in spring, then fade a