Observing the Transit of Venus scientifically was a milestone in our understanding of the solar system. However, to fully understand its ramifications, one must look at it in context – as one of many, some equally important, discoveries made by Humankind about the cosmos.
In their primitive youth, Humankind viewed the stars in
a much different light to today, yet made basic discoveries that have
come to be the foundation of modern astronomy. Many constellations still
bear names of animals and people, named many thousands of years ago based
on what they looked like. Other more sophisticated discoveries were made,
such as the phases of the moon, and the use of the sun and moon in telling
the time and as the basis for calendars. Early calendars were based around
the moon, which takes roughly 28 days to complete its phases: i.e. to
go from a “full” moon to a “new moon” and back
to another “full” moon. This calendar survives (albeit as
an adapted version) in the Chinese calendar. The 365-day calendar that
is now commonly in use was first used by the Ancient Egyptians, who had
discovered that flooding occurred every 365 days.
Stars were also used as guidance. Polynesian sailors, for example, used
the stars to find their direction while sailing the high seas. Other cultures,
such as the Babylonians, used stars to predict the future. The Tower of
Babel, as documented in the bible, was their attempt to build a stairway
to the heavens.
As Humankind’s curiosity about the stars grew and
grew, so too did their scientific knowledge. An early Greek astronomer
named Aristarchus was the first to put forth the idea of a Heliocentric
(or sun centred) “solar system”, though this belief was too
radical and so was widely disbelieved.
It was a widely held belief at the time that the Earth was flat (at least,
among the uneducated), and that if one were to sail too far, one would
fall off. Some theories elaborated on this, with one even stating that
the Earth was flat, but resided in a hollow ball. It was also believed
that the heavens never changed. Some theories put forth the idea that
the stars were lights set on heavenly bodies, set on perfect crystal spheres
moving around the Earth.
The first idea of a round, spherical earth can be traced to around the
6th century BC to Pythagoras. This was proved by another Greek astronomer,
Eratosthenes, who was the first to correctly calculate the size of the
earth. He did this by noticing that while the Sun was directly overhead
in one city, it cast shadows another city five hundred miles north. This
told him that the Earth was curved, and allowed him to calculate correctly
the approximate size of the Earth.
Ptolemy
Ptolemy was a Greek astronomer who put forth a revolutionary
theory that would be widely accepted for many years. His “Ptolemaic”
system involved the idea of a geocentric or “earth centred”
system. The sun, and the stars, revolved in circles around the Earth,
which was the centre of the universe. In his view, the Moon was the closest,
then Mercury, Venus, the Sun, Mars, Jupiter, and then Saturn. While this
may seem quite impossible to justify, Ptolemy’s system was sound
enough to accurately predict the movement of the planets for naked eye
observations.
This was detailed in his books commonly known as the Almagest, a mathematical description of the solar system. To explain this theory, Ptolemy used old calculations explaining planetary motion. The church would in turn adopt this theory for many years to come, until Copernicus in the 16th century. It is interesting to note, however, that Ptolemy’s view is more accurate than Copernicus’ view, which would not improve on Ptolemy’s view until the addition of Kepler’s laws. Another interesting aspect of his system is that it is doubtful that he believed in the reality of it – it is more than likely that he used it solely as a basis for his calculations.
The Church, which had been rising in popularity, was adopted as the main religion of the RoHumankind Empire. Because of the conflicting views held by the bible and scientific reason, the Church enforced a moratorium over scientific research that would last in the Western World for over a millennium, until the “Rebirth” of the Renaissance. This period would yield virtually no advances in the field of astronomy.
Thankfully, scientific research into astronomy continued in Asia and parts of the Middle East. Greek and Roman books on astronomy had been translated, and as such these cultures were able to both keep alive and build on the knowledge of the Greek and Roman cultures. Arabian astronomers invented the “star-finder” or astrolabe for solving complex astronomical problems.
At a point, the Greek books were translated back from Arabic, and so a strong base of knowledge, augmented by Arab scientific research, was available for the Europeans to build upon once more.
Copernicus
Copernicus, a Polish astronomer, decided that it would be simpler to place
the Sun at the centre of the Universe. His theory stated correctly that
the Earth rotated once on its axis daily and rotated once yearly around
the sun. This theory in turn implied that the other planets would revolve
around the sun also. Copernicus was reluctant to publish his theories,
being a perfectionist he was constantly working and improving upon it.
Also, his views would have gone against the church. He died in 1543, and
his views took many years to gather a following (it was banned in 1616
by the church). His theory was argued for many decades, and his influence
on modern astronomers such as Galileo should not be underrated, as his
was the basis for their theories.
Galileo
The invention of the telescope in Holland in the early 17th century would
revolutionise astronomy completely. The first person to realise its potential
was Galileo, who inspected the heavens through his “spyglass”,
making several discoveries, such as the detection of mountains and craters
on the moon. He also saw that Jupiter was orbited by several points of
light: its moons. The telescope’s ability to see many planets too
dim to see with the naked eye disproved once and for all the concept of
Ptolemy’s view of the universe. In many ways, Galileo and his “spyglass”
ushered in the age of modern astronomy.
The Transit of Venus
The Transit of Venus is the passage of Venus across the face of the sun.
This phenomenon was instrumental in understand the solar system, as it
provided a means for calculating the distance between the sun and the
Earth. First recorded by Jeremiah Horrocks in 1639, it has since been
recorded by many astronomers from all over the globe. Transits occur in
pairs eight years apart, with an interval between pairs of over a hundred
years. Edmund Halley (1656-1742) was the first to recognise its significance,
realising that by timing the passage of Venus across the Sun from multiple
places on Earth, the distance between the sun and Earth could be calculated.
By doing this, it was possible also to calculate the distances between
all the planets, and as such determine the scale of the solar system.
As Halley would not live to see the next transit, he located several suitable
sites for viewing and called upon the next generations to help his cause.
One such explorer was Captain Cook, who set out to the South Pacific to
observe the Transit. En route, he would discover many islands, including
New Zealand.
Probes
In the late 20th century, Humankind sent out several probes in the hope to discover
more about the nature of the outer solar system. They were instrumental
in discovering much of the nature of the outer planets. For example, from
the photos of Jupiter taken by the probe Voyager, scientists were able
to determine that the “Big Red Spot” was actually a giant
storm. Several other storms were discovered across the surface of Jupiter.
The probe also discovered several volcanoes on Jupiter’s moon Io
– the first ever to be discovered on another body.
While passing Saturn, the probe was able to discover that it had similar
atmospheric properties. It was also able to capture extra rings that were
not visible from Earth.
URANUS - the probe Voyager 2 discovered a magnetic field and haze layer,
as well as ten extra moons. On Uranus’ moon Miranda, it discovered
huge canyons up to 20 km deep and signs of great geological activity.
NEPTUNE - Voyager 2 revealed Neptune to be a very dynamic planet. Neptune
possesses several spots similar to those on Jupiter, and has the highest
winds of any planet, reaching up to 2000 km per hour. Images of Triton,
Neptune’s largest moon, revealed geyser-like eruptions of nitrogen
gas and dust being expelled far into its atmosphere.
The Mariner expeditions were also launched to gain information on some
of the inner planets. Mariner 2 was the first probe to monitor Venus,
measuring its temperature at more than 427 °C and a huge atmospheric
pressure of more than 100 times that of Earth.
Later Mariner models would also be launched toward Mars, with Mariner
9 actually becoming the first artificial satellite of another planet.
This probe sent over 7000 photos of Mars back to Earth, revealing its
great canyons, volcanos, and what looked like riverbeds.
Another Mariner was sent to Mercury, revealing it to be a cratered, hot
planet with an iron core (and therefore, a magnetic field) and a thin
atmosphere comprised of hydrogen.
Kepler
 http://www.kepler.arc.nasa.gov/PageMill_Resources/ellipse.gif |
The aforementioned Kepler’s Laws were indeed discovered by Johannes Kepler, a German astronomer, in the early 17th century. His first law documented that the planets move in ellipses, with the sun at the focus. This law was proved by a demonstration that elliptical orbits have the same period as circular ones, as they move faster near the focus but slower when at a greater distance from it. |
In trying to calculate the Earth’s position while in orbit, Kepler discovered his second law – that as the Earth sweeps out during its orbit, its radius vector describes equal areas in equal times.
His third law was discovered some ten years later in 1618.
He calculated that the squares of the period times of the planets orbiting
the sun are proportional to the cubes of the mean distances between the
planets and the sun.
It is interesting to note that this law, not the falling of an apple,
inspired Newton’s discovery of gravitation.
