INTRODUCTION What do you see in the sky? What comprises of the
solar system? The Sun The Moon The planets Mercury Venus Mars
Jupiter Saturn Fainter planets Uranus Neptune Asteroids Ancients
observed Positions of celestial bodies Attempted to describe the
motion of celestial bodies 9th - Physics
Slide 3
Constellations Ancients grouped stars into patterns Named the
patterns based on the imagined familiar objects and mythical
characters By Ptolmeys time 48 constellations have been known. By
Gallileo Gallileis time 60 constellations were known. Today the sky
is divided into 88 constellations Of these the 12 constellations
lying in the ecliptic are the zodiacal constellations
Constellations were used to define the positions of celestial
objects Motion of planets is confined to a narrow belt of the
zodiacal constellations Planetary motion is along the ecliptic
plane. 9th - Physics
Slide 4
Constellations Observing Moon and planets over a period of one
week night after night, Moon displaced more towards East. When the
planets do not even seem to shift at all. This is because Moon is
very near to us, when compared to planets. Similar effect is seen
when we observe an aero plane flying high. Aero plane appears to
fly slower when compared to the birds. The nearer planets like
Mercury and Venus show greater displacement than the farther
planets Jupiter and Saturn. On the New moon day, Moon sets at the
same time as the Sun, 15 days later Moon rises in the East, while
the sun sets in the West. All these facts can be drawn by studying
the positions against the backdrop of zodiacal constellations. 9th
- Physics
Slide 5
Constellations Constellations served as a fixed background
against which the motion of the planets can be observed. Mars is in
the constellation of scorpius or in Saggitarius indicates that Mars
is in the direction of the particular constellation Mars is just
located in that direction Planets are more nearer to Earth when
compared to the distance of the stars of the constellations Moon,
Mars and rest of the planets move in the eastward direction. This
eastward direction is called Direct Motion. Direct motion of Earth
is due to the rotation of the Earth. One can infer the motion as
well as the direction of motion of celestial bodies, with the aid
of constellations. 9th - Physics
Slide 6
Models of Solar system Early Greek astronomers assumed that
each planet went around the Earth in a small circle called
Epicycle. The centre of the Epicycle also followed a circular path
around the fixed Earth The model in which Earth remained fixed, and
all the celestial bodies revolved around it is called Geocentric
model of Ptolemy Planets Mercury and Venus are not visible
throughout the night. Mercury can be seen for a maximum duration of
two hours. Venus can be seen for about three hours. Geocentric
theory explained this phenomenon by assuming that the planets
Mercury and Venus went around the Earth in an orbit less than that
of the Sun. 9th - Physics
Slide 7
Helio Centric Theory Nicholas Copernicus (1473-1543) proposed a
model in which the Sun was at the Centre while all the planets
including the Earth moved around it. This theory is called
Helio-centric (sun centred) theory. Whatever motion that appears in
the sky is due to the motion of the Earth itself. Heliocentric
theory easily explained why Mercury and Venus did not appear
throughout the night. 9th - Physics
Slide 8
Distance Measurement - AU When Mercury is at the largest
separation from Sun, it makes 28 between the lines joining the
Sun-Earth and Sun-Mercury. Sun-Mercury can be expressed in terms of
Sun-Earth distance called Astronomical Unit(AU). 1AU ~ 150 Million
Km. AU is often employed as the basic unit of distance among solar
system objects Deductions of Copernicus on distance measurement
match very well with the current calculations. Distance measurement
is one of the key contributions of Helio centric theory. 9th -
Physics PlanetDistance CopernicanModern Mercury0.39 Venus0.72
Earth1.00 Mars1.52 Jupiter5.225.20 Saturn9.079.54
Slide 9
Laws of Planetary Motion Johannes kepler (1571-1630) perfected
the Heliocentric theory and described the motion as well as orbit
of planets. The orbit of Mars was unusually difficult. Kepler used
the accurate observations of the positions made by Tyco Brahe.
Kepler studied the motion of planets and stated three laws known as
Keplers laws of planetary motion. First law states that the orbit
of planets are elliptical. Second law refers to the period of the
planet. Third law refers to the speed of the planet at different
positions. 9th - Physics
Slide 10
Mercury Not much was known about Mercury until space probes
were launched in 1974 Mercury is small in size and is very close to
the sun Its surface temperature varies greatly It sets within two
hours of the sun setting or rises within two hours of the sun
rising. Like Earth, Mercury has a rocky surface It has no
atmosphere A striking feature of the planet Mercury is craters
Mercury revolves fastest around the Earth By the time Sun moves
from one high noon position to the next with respect to Mercury,
six months would have elapsed on the Earth 9th - Physics
Slide 11
Venus Venus is the brightest object in the sky next to the Moon
Its orbit is twice as large as Mercurys. The planet is visible for
a longer time than Mercury as much as three hours. Venus and the
Earth have almost the same size and mass. Temperature on Venus
remains a constant at 750K. A thick atmosphere of Carbon-di-oxide
along with the Sulphuric acid vapour envelopes the planet This
produces enormous pressure at the surface about 90 times on the
surface of the Earth The thick cloud reflects nearly 75% of the
light falling on it. This is the cause of brightness of Venus 9th -
Physics Green house effect: Carbon di oxide is opaque to heat. That
is all the heat generated within the planet is trapped. This causes
the temperature of Venus to steadily increase. This phenomenon is
known as Green house effect. A warning for what is in store for us
if global warming continues.
Slide 12
Mars Mars lies in an orbit larger than the Earth Seen all
through the night as a brilliant red object. The axis of rotation
is inclined at an angle of about 24 to its orbit. It experiences
Seasons as Earth does. It has a very thin atmosphere mostly
composed of Carbon-di-oxide It has two tiny moons called Phobos,
meaning fear and Deimos meaning panic, that swiftly around Mars.
9th - Physics
Slide 13
Asteroids Region between the orbits of Mars and Jupiter is
composed of planetsimals that did not combine to form larger bodies
like planets. They are small chunks of rocks and metal that orbit
the Sun. Largest asteroid is known as Ceres which has a diameter of
about 950 km. Asteroids are found to be between 2 and 3.5 AU from
the Sun. This region is called Asteroid belt. 9th - Physics
Slide 14
Jupiter Most massive Gaseous planet with a mass equal to that
of 318 Earths The volume is nearly 1400 times that of the Earths.
It accounts for 2/3 rds of all material outside the Sun in the
solar system. Inspite of huge mass and volume, it rotates fastest
among all the planets. Jupiter is chiefly composed of Helium and
Hydrogen gases, Conditions in the interior of Jupiter make it less
likely to harbour life. The inner temperature may be 13000K and
35000K. The pressure is million times that on the Earth Gallileo
discovered 4 moons of Jupiter Lo, Callisto, Ganymede and Europa.
Called as Gallilean Satellites. Gallilean satellites are the first
celestial objects discovered through telescope. 9th - Physics
Slide 15
Saturn Known for its beautiful rings Huge Gaseous planet Mainly
made up of Hydrogen and Helium Its atmosphere is mostly made up of
Methane, ammonia and water vapour Density of Saturn is less than
that of water Since the planet is far away from the sun, it is very
cold Saturns rings are composed of small, unconnected pieces of
rock and dust. This nature of rings was predicted four decades
before it was discovered. 9th - Physics The rings are tilted at an
angle to the orbit of saturn. The orientation, therefore appears to
change as seen from the Earth over one revolution of Saturn.
Slide 16
Uranus First planet invisible to naked eye and first planet to
be discovered by telescope. Discovered by William Herschel in 1781
Doubled the range of known solar system, Saturn is at the same
distance from Sun as Uranus is from Saturn. It receives only 1/400
th of the solar energy we receive on the Earth, But Its temperature
is not very low. Spacecraft Voyager does not reveal any evidence of
life. By 19 th century, astronomers could precisely predict the
position of Uranus This prediction was possible through Keplers
laws of motion along with Newtons law of Gravitation. The laws are
applicable well beyond the Earth, they are truly universal laws.
9th - Physics Rings of Uranus was discovered by Prof. J.C
Bhattacharya and Kuppusamy of Indian Institute of Astrophysics
Slide 17
Neptune & Great Pluto War Discovery of Neptune was entirely
due to the application of Newtons laws of motion and gravitation.
The fact that the laws govern the motion of bodies on the Earth
could be extended to motion of bodies elsewhere in the solar system
is a big leap in understanding the universe. Methane and Ammonia
form the bulk of Neptunes composition. This is another very cold
planet. 9th - Physics From the time of its discovery from 1930
until 2006, Pluto was considered as the ninth planet. Many objects
similar to Pluto were discovered in the outer parts of solar system
in late 20th and 21st centuries. The scattered disc like Eris is
20% more massive than Pluto. On August 24, 2006, the IAU defined
planet for the first time. This definition excluded Pluto from
planet hood and reclassified it under the new category of dwarf
planet along with Eris and Ceres.
Slide 18
Comets Comets are chiefly composed of water, carbon monoxide,
carbon di oxide, methane, ammonia and hydrogen cyanide all in
frozen state When comets are well beyond the orbit of Jupiter, they
are visible as dim objects only through powerful telescopes. As
they come closer to Sun, they grow brighter. All comets do not
become bright enough to be visible to naked eyes. Some comets like
Comet Halley is very bright. As comets approach Sun, their frozen
gases gradually vaporize. The energetic particles produced by the
Sun, pushes the gas away from the Sun, leading to the formation of
tail. The length of the tail increases as the comet approaches the
sun. And decreases as the comet goes away from the sun. The amount
of Suns heat reaching the comet as well as the mass of the gaseous
material in it decide the length of the tail. Keplers laws are used
to predict the positions of a comet during its journey. Using this
it can even be concluded that the comet is being observed for the
first time or it had been observed in the past. 9th - Physics
Slide 19
Planetary data 9th - Physics PlanetMean dist (AU) Diameter (m)
Mass (Kg) Range of Surface Temp(K) Mercury0.39100 to 623
Venus0.72750 Earth1.00183 x 333 Mars1.52133 to 293 Jupiter5.20163
Saturn9.5493 Uranus19.1957 Neptune30.0657
Slide 20
Structure of Earth The earths structure is classified as below
Crust Mantle Core Outer Core Inner core
Slide 21
Structure of Earth - Crust The part of earth where we stand is
called Crust It is about 30-40 km in thickness and is the outermost
layer It is composed of rocks and is also known as Lithosphere
(Lithos means rocks) The rocks are made of chemical compounds such
as oxygen and silicon It contains needed nutrients for the growth
and development of plants The crust provides food and shelter to
thousands of organism like earthworm, ants, termites.. Finally as
you know, it holds up lot of water that comes down as rain which is
important as far as life on earth is concerned Al Aluminum Fe Iron
Ca Calcium Na Sodium Mg Magnesium K Potassium T Titanium H -
Hydrogen
Slide 22
Structure of Earth - Mantle Mantle is the portion of the earth
below the crust It is about 2900 km in thickness It is composed of
silicates of iron and magnesium As crust is not deep, study of
features like composition, temperature and pressure is possible
using measuring instruments, while study of mantle needs to be done
by indirect means as it is too deep Hence study of mantle is done
by studying the vibrations caused by earth
Slide 23
Fact file Spiders are scientists tool Spiders weave a web and
wait for their prey As soon as they fly gets stuck, the spider
feels the vibrations The vibrations reach the spider from various
directions Spider analyzes the strength of vibration to find the
position and possibly the size of prey Hence, vibrations can be
used to detect objects and also to infer the nature of the object
The same principle is used by humans to understand the mantle
through earth quake vibrations
Slide 24
Structure of Earth - Core Core is the portion of the earth
below the mantle Its radius is about 3470 km, about half the size
of earth Temperature of core is about 4000 kelvin while the
pressure is very high Magnetic compass always aligns in north-south
direction any idea why is it so? Until 1600 AD this was believed to
be caused by a pole star, but Sir William Gilbert explained that
the alignment was due to earth behaving as giant magnetic field
Now, how does the earth behave as giant magnetic field? The
magnetic field is due to the motion of molten iron at the core and
this motion is caused by- Rotation of the earth as well as the
convection currents due to heat of molten iron
Slide 25
Atmosphere Atmosphere stretches of about few hundred
kilometers. For living process, up to a height 50 km is essential
Atmosphere composition: Major components includes nitrogen and
oxygen Nitrogen is key ingredient of amino acids Nitrogen is also
essential for plants But, plants cannot take nitrogen directly, so
Bacteria on earths crust helps plants to take nitrogen. They are
known as nitrogen-fixing bacteria Water vapor in the atmosphere is
the third component in the atmosphere important for weather
conditions
Slide 26
Layers of Atmosphere - Troposphere Atmosphere is classified
into different layers based on temperature and composition
TROPOSPHERE (tropos means heat) The layer nearest to the crust is
the troposphere It extends to a height of 11 km 75% of air
molecules that make up the atmosphere are found in troposphere
Oxygen and nitrogen the key elements of living organisms survival
float around in troposphere Troposphere is also important in
deciding the weather conditions, i.e fog, haze, rain
Slide 27
Layers of Atmosphere - Stratosphere The layer above the
troposphere is the stratosphere It extends to a height of 40 km
from troposphere It contains Ozone (an allotrope of oxygen).
Molecule of Oxygen is made of two atoms of oxygen but ozone
contains three atoms of oxygen (O3) Concentration of ozone is very
less ~ one molecule in four million Ozone plays an important role
is absorbing the harmful ultra-violet (UV) rays present in sunlight
Life on earth survives as Ozone acts as a shield from UV
radiation
Slide 28
Layers of Atmosphere - Hydrosphere 2/3 rd of earths surface is
water Water is the only liquid that exists in three state of matter
on earth As frozen ice caps, in ocean and as water vapor in
atmosphere Living organisms in oceans gradually increased the
content of oxygen in the atmosphere by biological process known as
photo synthesis With the production of oxygen came ozone and hence
the emergence of life on earth So, even hydrosphere influences the
composition of the atmosphere and in turn the life on land
Slide 29
Layers of Atmosphere Weather (Convection Current) A known fact
- Earth receives heat and light from Sun Air molecules on earth
gets heated up when the come in contact with heated land surface
Hot air is less dense than cold air So hot air rises up and
gradually gets cooled Meanwhile, the cold air that displaces the
hot air gets heated up Now this heated up air rises up. This
phenomenon, where hot air rises up and cold air coming down set up
the convection current Fact File This is the same principle seen in
boiling of water Hence, as heat energy is transported using the air
in atmosphere, the atmosphere acts as a heat distribution
system
Slide 30
Layers of Atmosphere Weather (Water Cycle) Water in the earth
also plays an important role in heat energy distribution As we
already know, water covers 2/3 rd of earths surface Water in lakes,
seas and ocean vaporize slowly due to the suns heat But, as water
has a high specific heat, hence, lot of heat energy is needed for
water to vaporize The water vapor that rises in the atmosphere,
stays there in the atmosphere and forms clouds with dust particles
When the clouds condense and cool, water vapor changes to liquid
form and comes down as rain. This is how we get rainfall on earth
This phenomenon is called the Water Cylce The processes Convection
Current and the Water cycle ensures pleasant weather conditions on
earth
Slide 31
Layers of Atmosphere Weather The processes Convection Current
and the Water cycle help matter to move in vertical direction only
This would not be much help in distributing heat energy across the
globe The earths rotation ensures that the moving air is deflected
from its vertical path As the air rises up vertically, it is
subjected to a sideward force due to earths rotation Hence, the air
rises up and moves side wards resulting in distribution of heat
energy over larger surface area of the earth
Slide 32
Fact File - Water Water is a wonderful and much needed compound
to sustain life on earth Nearly 70% of the cell is water Water
dissolves a number of compounds like Carbon di-oxide and oxygen and
salts in the body Water is essential for blood circulation Force of
attraction among molecules of water aids capillary action, this
helps plants to reach leaves Carbon di-oxide and water combine to
produce carbohydrate As water freezes, its volume increases, and
because of this ice floats on water This unique property helps the
cells on seas and oceans to survive
Slide 33
Earth as a dynamic system Earth appears static, But the truth
is that Earth is working actively all the time. It receives energy
from the Sun, drives convection current in the atmosphere, sets up
water cycle process all the time. It rotates continuously and
distributes the water and air molecules and energy all over the
planet. Earth is very much like a living system. A living system
has several individual parts. The individual parts cannot
exclusively constitute a system. The basic factor is co-ordination.
Earth co-ordinates among all its individual components - living as
well as non-living. 9th - Physics