Transcript U3A-Mars01 6101KB Nov 18 2013 08:49:29 PM

SESSION 1
GENERAL INTRODUCTION
HISTORY
• Humankind has long been fascinated by the
heavens
• The Sun and Moon played dominant parts in
many early religions
• We probably began to study the heavens
about 10,000 years ago with the introduction
of agriculture
• Shamans became a privileged class whose
needs were looked after by the local
community enabling them to study the night
sky amongst many other things
SUMERIAN OBSERVATIONS
• The oldest written observations were
made by the Sumerians about 5,000
years ago
• They believe the Earth was a flat
motionless platform covered by a dome
where the Gods played around with the
sun, moon and stars
• However, some stars did not appear to
follow the rules
THE PLANETS
• Nearly all stars kept constant relationships to
one another
• However, five that could be observed with
the naked eye appeared to walk about the
sky independently. They are the ones that
were called “wanderers” or “planets”
• They are now known as Mercury, Venus,
Mars, Jupiter and Saturn after major figures
in Roman mythology. Mars attracted special
attention because of its reddish colour and
became associated with war and conflict
BIRTH OF ASTRONOMY (1)
• The Greeks made major contributions
to our understanding of the solar
system
• Aristotle concluded the earth was
probably round because its shadow on
the moon during a lunar eclipse was
curved
• Aristarchus found that the Sun, not the
Earth, was the centre of the planetary
system and that the Earth was simply
another planet orbiting around the sun.
He also concluded that the Earth
rotated around its axis
BIRTH OF ASTRONOMY (2)
• The Greek astronomer Hipparchus,
who lived on the island of Rhodes at
about 150 BC worked out a system for
predicting the positions of the Sun and
Moon at any time of the year
• He even calculated the distance
between the Earth and the Moon
(384,400 km)
PTOLEMY
• He lived in the second century AD and
believed in a stationary Earth located in
the centre of the Universe with all the
other heavenly bodies moving around it
• He argued that the Earth could not
possibly be spinning around its axis
because, if it did, the birds would fly off
their perches
PTOLEMY (continued)
• At this time it was known that some planets
appeared to reverse direction – a
phenomenon that was particularly obvious in
the case of Mars
• He attempted to explain this by suggesting
that the planets were moving in small circles
(epicircles), at the same time as they
revolved around the Earth
• During the Middle Ages his ideas
unfortunately became part of the dogma of
the Roman Catholic Church
COPERNICUS
• He published a manuscript in 1543 in
which he placed the Sun in the centre
with the Earth and the other planets
moving around it but he also believed
that they were travelling at constant
velocity in circular orbits
• Aristarchus had suggested this model
1,800 years earlier. Copernicus was
aware of this and credited him with the
original discovery
JOHANNES KEPLER
• In the early 1,600’s he used high quality
astronomical observations by Danish
scientist Tycho Brahe to hypothesize
that the planets traveled around the
Sun in elliptical orbits with the Sun
located in one of the foci
• The planets move fastest at perihelion
and slowest when they are at aphelion
Mars travels much further per unit time when
in perihelion than in aphelion
With the Sun at the centre
of the solar system the
apparent reversal of the
course of Mars is easily
explained
OTHER ACHIEVEMENTS
• Kepler correctly calculated the relative
distances of the planets from the Sun
• The distance from the Earth to the Sun
was unknown so Kepler called it one
astronomical unit, now known to be
149.51 million km measured by radar in
the 20th Century
• He showed that Mars was an average
distance of 1.523 astronomical units
from the Sun or 227.72 million km
GALILEO
• He was an Italian astronomer at the
University of Padua who adopted
Kepler’s ideas after reading his book
“Astronomia Nova”
• In the same year heard about the
invention of a primitive telescope by
the Dutch astronomer Huygens.
• He started to build a succession of
telescopes the best of which had 32X
magnification
MARS THROUGH THE
TELESCOPE
• Galileo became the first human being
to examine Mars through a telescope
but could not see any details probably
due to unfavourable conditions
• The distance from Earth to Mars varies
from 78 to 399 million km depending on
whether they are on the same or on
opposite sides of the solar system –
approximately a two year cycle
• Mars features can also be obscured by
occasional dust storms
VENUS THROUGH THE
TELESCOPE
• Galileo also studied Venus and found
that like the Moon it went through a full
range of phases from a narrow
crescent to practically full
• This told him that Ptolemy’s Earth
centered model of the solar system had
to be incorrect
At left is Ptolemy’s model of the solar system
with the Earth at the centre. At right is the
solar centred model of Galileo based on his
study of the phases of Venus
NEW MOONS
• In 1610, while examining Jupiter
through one of his telescopes, Galileo
discovered four moons rotating around
the planet. The Earth was not the only
planet with a moon
• He also observed Saturn and
discovered its rings but could not
figure out what they were
HUYGENS
• Huygens was the first astronomer to
identify a surface feature on the planet
Mars. He discovered a dark v-shaped
marking now known as Syrtus Major
• From its movement he was able to
calculate that Mars turned around its
axis at almost the same time as Earth
(24 hours and 38 minutes)
• He also discovered the south polar ice
cap. The north polar icecap was
discovered a few years later
GALILEO IN RETREAT
• The Roman Catholic Church took a dim
view of his sun centered model of the
solar system and in 1616 he was told to
stop teaching heresies
• In 1632 he published a book explaining
his hypothesis. He narrowly escaped
being burnt at the stake and was forced
to recant his views. He died in 1642
while still under house arrest
• It took the church another 100 years to
accept his views
GIORDANO BRUNO
• He was a scholarly Catholic cleric living
in Italy in about 1,600 AD who dared to
suggest that the Universe might
contain other inhabited worlds, a view
that is quite popular today
• His views so enraged the Church that
he was burnt alive at the stake
NEWTON
• In 1687 Newton formulated his laws of
gravity together with their mathematical
proof
• He found that all objects attract one
another in direct proportion to their
mass and in inverse proportion to the
distance between them
• It made it possible to predict the
movement of bodies in the solar
system with uncanny accuracy
• The same laws are still used today in
the navigation of space probes
IMPROVED TELESCOPES
• Newton also designed a new reflecting
telescope with a concave lens and a flat
mirror which produced much sharper
images than earlier instruments
• This type of telescope was used by
William Herschel in 1781 to discover
the planet Uranus, the first discovery of
a new planet since ancient times