Mercury
in History and Culture |
 Mercury
and ancient cultures
Since
ancient times, humankind has attached great significance to the
motions of heavenly objects. The world's peoples have long observed
the sky, fascinated by the rising and setting of the Sun, the
phases of the Moon, and the paths of the stars and the visible
planets - Mercury, Venus, Mars, Jupiter, and Saturn. The motions
of planets and stars were used to navigate, and to track the passage
of time.
Astronomy
was often intertwined with religious practice, and the planets,
Moon and Sun identified with a pantheon of gods. Long ago astronomers
were frequently priests and astrologers as well, seeking to relate
human events to celestial motions. In some early cultures the
motions of astronomical objects were carefully recorded, so that
by constructing accurate calendars, human futures might be predicted.
Mercury is the most difficult to see of all the terrestrial planets,
because it never is far from the Sun. Yet we know from their records
that many ancient cultures kept watch on Mercury, noting its swift
movement in the sky and often associating with it a messenger
god, or a god of wisdom and knowledge.
The
map below indicates some areas of the world in which ancient peoples
left clear evidence of their observation of Mercury. To learn
more about what mysteries the planet held for these peoples, select
any shaded region below.
|
 Mercury
in modern times
The
invention of the telescope allowed astronomers to get a closer
view of the planets, the Sun and the Moon. In 1609 the Italian
scientist Galileo developed the
first telescope suitable for astronomical observation, and turned
this new instrument toward the Moon, Jupiter and Venus. A year
later he made the first telescopic observation of Mercury, but
found himself unable to get a clear view of the planet. In 1639
another Italian, Giovanni Zupus,
studied Mercury’s orbit with the aid of a more powerful
telescope. He discovered that, like the Moon and Venus, Mercury
has phases. This provided additional evidence for Copernicus’
heliocentric
view – that Mercury and the other planets orbit the Sun.
| Odd
but true: Although it was not until the mid-1600's
that the heliocentric model became the predominant view of
the solar system, certain Greeks 2000 years earlier already
believed this to be true. The astronomer Aristarchus
of Samos (310 – 230 B.C.) proposed that all the
known planets rotate around the Sun, and that the Earth rotates
on its axis once each day. |
By
the late 1700’s Johann Hieronymus
Schroeter, working in Germany, had observed and sketched Mercury’s
surface. Some 100 years later, Giovanni
Schiaparelli observed Mercury over a seven year time frame
and, based on the day-to-day positions of surface features, concluded
that Mercury’s rotational period is the same as the period
of its orbit around the Sun. Schiaparelli claimed that both the
rotational period and the orbital period were 88 Earth days long,
so that the same side of Mercury always faces the Sun (just as
the same side of the Moon always faces the Earth). This “fact”
remained unchallenged for almost 75 years.
The
theory that Mercury is in synchronous rotation with its orbital
motion was shattered in 1965. Astronomers Gordon
Pettengill and Rolf Dyce used
a radio telescope to make radar observations of Mercury’s
spin rate. They found that Mercury’s rotation period is
only 58.6 Earth days, not the 88 days accepted for nearly a century.
NASA
made the first plans to send a spacecraft to the inner planets
in 1971, when it was realized that three years later Venus and
Mercury would be positioned so that a single probe could reach
both with minimal cost and fuel. The resulting $98 million mission,
named Mariner 10, made its first flyby of Mercury on March 29,
1974 at a distance of about 700 kilometers. This probe provided
us with the first close-up photographs of Mercury’s surface.
In three separate flybys, Mariner 10 was able to image slightly
less than half the planet’s surface, revealing topography
much like that of our Moon. But unlike the Moon, the photographs
showed regions of huge scarps (cliffs) ranging as high as 3 kilometers.
On-board instruments indicated that other features of Mercury
are also not very Moonlike: It has a large iron core, a trace
atmosphere, and a weak magnetic field. Mariner 10 also found that
Mercury is more nearly spherical than is the Earth. Learn more
about this mission by visiting NASA's Mariner
10 website.
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