Spencer Loftus
Astronomy: Module 1 – Introduction to Astronomy
The Ancient View
Judging by appearances can be often misleading, especially in astronomy. For
example, the earliest humans thought the earth was flat with endless surface
and the sky was a huge dome with stars fixed on it. They believed the earth was
the most important thing in the universe, with the sun and moon serving as
lights for day and night, controlled by gods.
Overtime, people began to question simple ideas. They wondered what held up
earth and what kept the sky from collapsing. Myths began to emerge to explain
these mysteries. The Hindus imagined the earth was supported by four elephants
standing on a giant tortoise floating on an ocean. The Greeks however had the
story of Atlas, who was punished to hold up the sky forever.
Eventually, people started to understand more about the true nature of the
universe. Greek philosophers realized the earth was spherical, like a football.
They were right about that, but they wrongly believed the earth was the centre
of the universe.
By the second century AD, the
early philosophers’ ideas had
solidified into a specific theory,
which despite being incorrect
by today’s standards, was
widely accepted until about 400
years ago. This theory is known
as the Ptolemaic System,
named after Claudius Ptolemy
of Alexandria (100-170 AD), a
famous ancient astronomer
who first clearly articulated this
view of the universe.
Claudius believed that the Earth
was at the centre of the
universe, with the Moon,
Mercury, Venus, the Sun, Mars,
Jupiter, and Saturn orbiting around it in that order. Beyond these planets, the
stars were thought to be fixed on the backgrounds of the heavens.
The Ptolemaic system remained unchallenged for about 1,400 years after
Ptolemy’s death. People liked the idea that Earth was the most important part of
nature, staying still at the centre of the universe, while everything else revolved
around it.
The modern View
Less than four hundred years ago, the modern Copernican theory replaced the
long-standing Ptolemaic system. In this new theory, proposed by German
astronomer Nicholas Copernicus (1473-1543) in the mid-sixteenth century, the
Earth was no longer seen as the centre of the universe. Instead, it was
considered just one of many planets orbiting the sun.
,Spencer Loftus
The Sun, which is the most important celestial body for us, sits at the centre of
the Solar System, not the entire universe. The planets Mercury, Venus, Earth,
Mars, Jupiter, Saturn, Uranus, Neptune orbit around the sun in that order. The
stars are scattered far beyond the Solar System, at great distances. Mercury and
Venus are called the inferior planets because they orbit closer to the Sun than
Earth does. The other planets, except Earth, are called superior planets because
their orbits are outside of Earth’s path around the sun.
The Five planets Mercury, Venus, Mars, Jupiter, and Saturn have been known
since ancient times. However, it has only been 127 years since the first new
planet was discovered by observing the sky, highlighting the rapid progress in
modern astronomy. On March 13th, 1781, while observing the constellation
Gemini, the famous Sir William Herschel Spotted an unfamiliar object. He first
thought it was a comet, but after a few days of watching its movements, he
realized it was a planet. This object, now known as Uranus, was identified
through the power of the telescope. Its discovery instantly doubled the known
boundaries of the Solar System and sparked hope that more planets might be
found in the future.
For many years before Herschel’s discovery, astronomers
had noticed that the distances of the
known planets from the Sun
seemed to follow a pattern,
called Bode’s Law. The
discovery of Uranus fit this
pattern well. However, there was still a large
gap between the orbits of Mars and
Jupiter.
The Solar System would have
seemed almost perfectly orderly if
there had been another planet
between Mars and Jupiter.
However, this space, where
one would expect to find another planet, was mysteriously empty.
At the start of the nineteenth century, the mystery of the empty space between
Mars and Jupiter was solved. Astronomers discovered a small object orbiting
space, but it was too tiny to be considered a full-fledged planet. The next year,
another small object was found in the same area, even smaller than the first.
Over the next years, two more of these small bodies were discovered. Then,
, Spencer Loftus
there was a pause, and no more were found until halfway through the century
when the discovery of these “minor planets” resumed. These small bodies were
named Asteroids or Planetoids. Since
then, discoveries in this part of our Solar
System have been frequent. Currently,
there are six hundred known asteroids
orbiting in the space between Mars and
Jupiter that was previously empty.
In 1846, the outer edge of the Solar
System was expanded with the discovery
of a large planet beyond Uranus. This new
planet, named Neptune, was found
through separate calculations by French
astronomer Le Verrier and Cambridge
mathematician Adams. Unlike the
discovery of Uranus, which was made
during a routine observation of the sky,
Neptune was found through specific
mathematical predictions.
On the contrary, the position of Neptune was predicted through careful
mathematical calculations aimed at finding a distant and unseen celestial body.
This body’s gravitational pull was affecting Uranus’ orbit around the Sun. Adams
completed his calculations first, but a delay in searching the predicted area of
the sky at Cambridge allowed France to claim the discovery. Eventually, the new
planet was spotted near the predicted location by observer Galle in Berlin,
confirming Le Verrier’s mathematical prediction.
Almost fifty years later, in recent times, another discovery was made in our Solar
System. One of the newest members of the asteroid family, a small object found
in 1898, was found to be orbiting Earth instead of Mars, unlike most asteroids
which orbit between Mars and Jupiter. This object, named Eros (which means
Cupid in Greek), is only about twenty miles in size, much smaller than other
major objects in the Solar System.
That’s the complete list of
planets we know about.
Whether there are more out
there, only time will tell.
Some have suggested there
might be a planet closer to
the Sun than Mercury. A few
others have been thought to
exist beyond Neptune’s orbit.
In 1859, a French doctor
named Lescarbault claimed to
have found such a planet,
named “Vulcan”, but there
hasn’t been enough evidence
to confirm its existence. The
brightness of the Sun’s
