|How did people discover the planets?
|Question Date: 1999-06-08|
I think that the first people to discover that
planets were not just stars were Arab astronomers
who lived roughly a thousand years ago. They kept
careful track of the positions of all the stars in
the sky, and noticed that nearly all of them moved
in very predictable circular paths, rising in the
east and setting in the west each night. There
were a few objects, however, which didn't follow
such simple behavior. They rose in the east and
set in the west, but they wandered around in the
sky in much more complicated paths than all the
other stars. They called these funny objects
"planets", which I believe means "wanderers" in
arabic. The ones which they could see (they had no
telescopes) were Mercury, Venus, Mars, Jupiter,
and Saturn. When people invented telescopes
(Galilleo was the first to study the sky with
telescopes) the could see other, fainter planets:
Uranus, Neptune, and Pluto. In addition, they
could see that nearly all of these planets had
moons of their own. You could find out more
information about the planets and the telescopes
used to study them in your library, or on the NASA
For many centuries people have looked carefully at
the night skies and all the object visible
there.They were able to track how these objects
move, and noticed that some of them move in very
different paths than the majority of the objects.
Some of these erratically-moving objects are the
planets in our solar system. What are some of the
other objects that these ancient people
discovered? I'll give you a hint on one of the
type - when was the first recorded sighting of the
object now known as Haley's Comet?
The word planet means "wanderer" Greek. Ancient
peoples who studied the sky could see that most of
the stars in the sky moved across the sky through
the night together in a specific way. But there
were a few bright stars that didn't follow this
pattern and "wandered" across the sky in different
paths. These stars were seen as special because
of their brightness and unusual paths and were
often associated with gods or events (the names we
have for the planets come from the names the
romans gave them which were based on roman gods).
But most of these ancient people thought that
the planets were just unusual stars and didn't
think they could be rocky objects like the Earth
that were just reflecting the light of the Sun.
It wasn't until the 17th century that people
looked closely at the planets through telescopes
and realized that they weren't just points of
light and had features on their surface (Galileo
is credited with first doing this). Galileo was
the first to write about planets as objects like
the Earth or Moon and since then, our
understanding of the planets has become much
greater with further observation by telescope, and
more recently, with space probes sent to look
closely at the planets. What do you think people
thought when Galileo first wrote about there being
other planets like ours?
Planets have been known since the beginning of
recorded history as special objects in the
heavens-- They being the only objects that moved.
From a visual point of view, planets get brighter,
dimmer, move across the sky -- stop and turn
around, but always stay close to the Zodiac or the
ecliptic or the path of the sun across the sky.
From that point of view, the planets: Mercury,
Venus, Mars, Jupiter and Saturn have all been
known since the most ancient times. However, It
was not until the work of Gallileo and Kopernicus
that scientists developed a sun-centered model for
the solar system, and realized that planets must
be massive bodies in orbits. Galileo was first to
use a telescope to observe the moons of Jupiter --
and published his views in defiance of the church.
This was late in the 16th century.
was the first planet discovered in modern times --
by observations of William Herschel in 1781. Many
earlier people had seen it, but because they
didn't make systematic maps, they missed its
motion across the sky.
After Uranus, there
was a flurry of interest to discover yet more
planets... However, by careful analysis of the
measured orbit of Uranus, astronomers John Adams
and Urbain Le'Verrier predicted there must be a
more distant planet -- it was finally found by
Galle and D'Arrest in 1846.
planets are easy binocular objects, and are in the
summer sky -- pick up a copy of Astronomy or Sky
and Telescope for easy instructions to find
Pluto was discovered in 1930 by
Clyde Tombaugh -- (who died in 1997) it is much
smaller and harder to find in the sky, even with a
telescope. It was thought that there had to be a
larger planet because of discrepencies in the
calculations of the orbits of Uranus and Neptune
-- but this was later shown to be an error. It is
unlikely that there is another planet in our solar
system -- unless it is very far out from the sun.
It would be detected by its gravitational effects
on the known planets.
Please check out the
if you have a pair of binoculars, take a look at
Jupiter and the other planets... It is easy to
pick out the four moons of Jupiter and fun to draw
the positions on a few consecutive nights... They
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