Solar system
Universe.
Early Astronomy.
Calendars.
Heliocentric model.
Birth of the solar system.
Sun.
Kepler's Law.
Mercury.
Venus.
Mars.
Jupiter.
Saturn.
Uranus.
Neptune.
Earth's orbit.
Earth's rotation.
Earth's axial tilt.
Geological timescale.
Current structure of the earth.
Inner core.
Outer core.
Mantle.
Lithosphere.
Crust.
Tectonics.
Earth's magnetic field.
Hydrosphere.
Atmosphere.
Moon.
Dwarf planets.
Asteroid belt.
Meteors.
Kulper belt.
Comet.
Oort cloud.
Universe.
About 14 billion years ago, there was a big bang.
The universe was born.
The stars were born, at some point of time after this.
This theory of the universe, is called as the big bang theory.
Since then, the universe has been expanding.
We do not know exactly, how big the universe is.
We can only estimate, the size of the observable universe.
To state the size of the universe, we need a more convenient unit.
The velocity of light, is the limit of the velocity, that any object can reach.
The distance travelled by light, in one year, is about 6 trillion km.
This distance is called as a light year.
This is a more convenient unit, to discuss distances in the universe.
The size of the observable universe, is about 93 billion light years.
The universe is dynamic.
The universe is expanding.
New stars are being born, and old stars die.
These events happen over billions of years.
We do not know, exactly how many stars are there, in the universe.
The current estimate, is that there are 300 into 10 to the power of 23,
or 300 sextillion stars, in the universe.
Our sun is one of these stars.
Stars tend to cluster together.
These clusters of stars, are called galaxies.
There are probably 100 billion galaxies, in the observable universe.
Each galaxy can have, as little as 10 million stars,
or as many as 1 trillion stars.
Our sun, belongs to a galaxy, called as the “Milky way”
Our galaxy has about 10 billion stars.
It is about 100 thousand light years, in diameter.
Our sun is not even in the centre of our galaxy.
Our sun is about 28000 light years, from the centre,
in the rim of the Orion Arm, of the milky way.
This in brief, is the address, of our sun, and our solar system,
in the universe.
As you can see, it is not a very prominent address.
An alien is unlikely to give our star, the sun, as a landmark in the universe.
Our closest nearby neighbouring galaxy, is the andromeda galaxy.
It is about 2.5 million light years away.
Our nearest neighbouring star, is the Proxima Centauri.
It is about 4 light years away.
Early Astronomy.
Early human beings, were always fascinated,
by the sun, the moon, the sky, and the stars.
One of the earliest science to develop, was astronomy.
At that time, astronomy was closely associated with mythology, and religion.
Today we call, early astronomy as astrology.
At that time they believed that the earth, was the centre of the universe.
They believed that the sun and the stars, went around the earth.
They were keen enough to observe, that some stars seem to move in their position,
in the sky, relative to other stars.
They called these objects, as wandering stars.
The word planet, comes from the greek word, “Wanderers “.
At one point, the sun and the moon were also considered as planets.
In many civilisations planets were considered as gods.
Ptolemy was one of the early Greek astronomer, who lived in the 2nd century BC.
He proposed the Earth centric, or geocentric model of the solar system.
In this model, the Earth was at the centre.
The sun, the moon, and the planets circled the Earth.
Ptolemy’s model was the basis for early astronomy, for more than thousand years.
Calendars.
The movement of celestial objects, were the basis of time, and the calendar.
The passage of the sun, marked the time of the day.
Sun dials were the earliest clocks, used by humans.
The passage of the sun, differentiated day and night,
and defined a day.
Early astronomers considered the sun, and the moon as planets.
They knew of, five real planets.
They were Mercury, Venus, Mars, Jupiter and Saturn.
The days of the week, were named after the planets.
The phases of the moon, were used to define a month.
It is now called as a lunar month.
Seasons were very important, to early civilisations.
The agricultural cycle, was dependent on the seasons.
In locations where the winter was harsh,
preparations had to be made, for the winter.
Forecasting the seasons, became an important factor,
for developing a solar calendar.
Early astronomers noticed, the length of the day, varied from season to season.
They also observed, a pattern, in the angle at which the sun rose.
This pattern repeated itself consistently, over a period,
which happened to be a solar year.
In spring for example, the sun rose from a particular angle.
This, in many calendars, marked the beginning of a new year.
All these celestial observations led to developing a rough solar calendar.
The concept of the year was born.
The time, the date, the day, the month, became sub divisions of the year.
The calendar was by no means perfect, and varied from civilisation to civilisation.
The solar calendar however served a useful and practical purpose.
This calendar evolved, and was refined over time.
The basis of the calendar we use today, had its basis in early astronomy.
Heliocentric model.
Since the dawn of civilisation, till the 17th century,
it was widely believed, that the Earth was the centre of the universe.
It is only after the findings of Copernicus and Galileo,
it was realised that the Earth is not the centre of the universe.
Astronomers like Copernicus, Galileo, and Kepler,
developed the sun centric, or heliocentric model of the solar system.
The sun is at the centre of the solar system.
Earth is one of the planets of the sun.
Mercury, Venus, Earth, Mars, Jupiter, Saturn, and Neptune are the planets,
in the solar system.
All the planets orbit the sun, in a predictable elliptical path.
Newton’s gravitation theory, helped to understand, the orbits of the planets,
around the sun.
We now know that what we thought, as “Wandering stars”, are actually planets.
The stars, are other suns, located many light years away from, our sun.
They look so small to us, because of the large distance, from us.
The sun, which is our own star, is very prominent,
because of it’s relative proximity.
Apart from the planets, other celestial objects, like dwarf planets,
asteroids, meteorites, and comets, also orbit the sun.
The sun is the very basis of our solar system’s existence.
Birth of the solar system.
The universe, is about 14 billion years old.
Our sun is relatively, a young star.
It was born about 4.6 billion years ago.
It was born due to the gravitational collapse,
of a part of a giant molecular cloud.
Most of the collapsing mass, collected in the centre, and became the sun.
More than 99.8% of the mass of the solar system, is in the sun.
The rest of the gas, from the molecular cloud, flowed around it.
These eventually coalesced, to form the planets.
All these planets orbited the sun.
The major planets are,
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
Mercury is the closest planet to the sun.
Neptune is the farthest away from the sun.
The other planets have orbits around the sun, between Mercury and Neptune.
The four planets closest to the sun, are,
Mercury, Venus, Earth and Mars.
They are called terrestrial planets.
They are comprised of solid mass, like rocks.
Our neighbouring planets, are Venus on one side, and Mars on the other side.
The outer four planets are,
Jupiter, Saturn, Uranus and Neptune.
They are called as gas giants.
99% of all the mass, in all the planets, is located in these four gas giants.
The mass in these planets are mostly gas and ice.
Less than 0.2% of all the mass in the solar system, is in the planets.
Considering these facts, makes us realise how small the Earth is,
in the solar system.
However, Earth is a very special planet.
It is located in what is called as the Goldilocks zone.
It is neither to close to the sun, which would have made it too hot,
or too far from the sun, which would have made it too cold.
Many conditions in Earth, make it suitable for life.
It is the only planet in the solar system, which is known to sustain life.
All other planets, to the best of our current knowledge, are lifeless.
Apart from these major planets, there are also some dwarf planets,
like Pluto and Ceres.
The rest of the gas formed smaller objects,
like asteroids, meteorites, and comets.
Sun.
The Sun is at the centre of our solar system.
99.86% of all the mass, in the solar system, is in the sun.
The Sun is just one of the 300 sextillion stars, in the universe.
The universe is dynamic.
Stars have a life cycle.
Stars also have widely different sizes.
It is very difficult to judge, the size of the star, based on it’s brightness.
Stars which are very distant, will look fainter, though they might be bigger.
All the stars cannot be seen by the naked eye.
Scientists use sophisticated equipment to study astronomy.
Many of the observatories are located, in remote places, in Earth.
Some of them, like the Hubble space telescope, are in orbit.
Astronomy is an exciting science.
New discoveries are being made, by astronomers even today.
Like other stars, the sun was born, when a giant molecular cloud collapsed.
It is thought, that this molecular cloud was about 1 light year across.
That is about 6 trillion kilometers.
This is about 10 million times, the diameter of the Sun.
It is possible, that some other stars, were also born, along with our Sun.
Our Sun a star, was born about 4.6 billion years ago.
Based on their observations, astronomers have classified the stars.
Our Sun, is classified as a yellow dwarf.
This name is misleading, because, the Sun is neither yellow,
nor is it a dwarf.
It is only a convenient way, to classify certain type of stars.
It is more scientifically called, as a G-type main sequence star.
The Sun has a life cycle, of about 10 billion years.
It is approximately at half it’s life cycle.
It is expected that, it will evolve, to become a red giant.
At some point, it will explode, and lose most of it’s mass.
It will eventually, become a white dwarf.
There is no cause for worry.
The Sun will remain like it is now, for more than four billion years.
Considering that, we human beings existed for only 200 thousand years,
the Sun will continue to exist, in the foreseeable future.
The Sun has a radius of about 700 thousand kilometers.
It is so huge, that about 1.3 million Earths can fit into it.
The Earth is about 150 million kilometers, from the Sun.
It is so far away, that light from the Sun, takes about 8 minutes to reach the Earth.
The Sun comprises, of mainly two of the lightest elements.
Hydrogen and Helium.
Surprisingly Helium, was first detected in the Sun.
About 75% of the Sun comprises of hydrogen.
About 24% of the Sun comprises of helium.
The Sun is a very active nuclear reactor.
The energy of the Sun, comes as the result of this continuous nuclear reactions.
In the core of the Sun, hydrogen is being continuously converted to helium.
This process is known as nuclear fusion.
During this process, matter is being transformed to energy.
Every second more than 4 million tonnes of matter, is converted to energy.
Hydrogen is the fuel for the nuclear fusion reaction.
Nuclear fusion releases enormous amounts of energy.
The core of the Sun, is very hot.
The temperature can reach up to about 15.7 million degrees Kelvin.
This energy generated by the Sun, radiates through out the solar system.
All the planets, from Mercury to Neptune, receive this energy.
Most of this energy, is radiated as light energy.
When we refer to solar energy,
we are referring to, the light energy, coming from the Sun.
The light energy comprises of, visible light, infra red light, and ultra violet rays.
It is solar energy, which sustains life on Earth.
The Sun has a huge mass.
It’s mass is estimated to be about 2 into 10 to the power of 30 kg.
This huge mass, results in a strong gravitational field around the Sun.
The force of this gravitational field can be felt for 100s of millions,
of kilometers around the Sun.
It is this gravitational force, which causes the planets to orbit the Sun.
Kepler’s Laws.
All the planets orbit the Sun.
It was initially thought, by earlier astronomers, that the orbit of the planets,
around the Sun, was circular.
Kepler was a mathematician, astrologer, and astronomer.
This was a time, when the distinction between astrology and astronomy,
was not very clear.
Kepler worked out, a more accurate mathematical model,
of the orbit of the planets.
He discovered that the orbits, were not circular,
but elliptical.
A ellipse is like a compressed circle.
It has two focal points.
These are called as foci.
It has a semi minor axis, which is shorter.
It has a semi major axis, which is longer.
Kepler discovered the elliptical orbital path, of the planets.
Kepler formulated the rules, which govern the orbits of the planets.
These are called as Kepler’s laws, of planetary motion.
Kepler’s first law.
The orbit of a planet, is an ellipse, with the Sun, at one of the foci.
In an elliptical orbit, the planet is at some time close to the Sun,
and at some time, far from the Sun.
The closest point to the Sun, is called as the apogee.
The furthest point to the Sun, is called as the perigee.
Kepler’s second law.
A line segment joining a planet,
sweeps out equal areas,
during equal intervals of time.
When the planet is closer to the Sun, it moves faster.
When it is further from the Sun, it moves slower.
Kepler’s third law.
The square of the orbital period of a planet,
is proportional to the cube,
of the semi major axis of it’s orbit.
All the planets obey, Kepler’s laws of motion.
Newton’s law of universal gravitation, was discovered much later.
It correlated very well, with Kepler’s laws of planetary motion.
Mercury.
Mercury is the planet, which is nearest to the Sun.
It is named after the roman messenger God.
In India, it was referred to by the deity Buudha.
Mercury orbits the Sun, at a distance of about 57 million km.
Planets which are closer to the Sun, compared to Earth,
orbit the Sun, faster than Earth.
It orbits the Sun, once in 88 Earth days.
Mercury is a very small planet.
About 16 planets, of the size of mercury, can fit into our Earth.
Mercury is one of the terrestrial planets.
It has a solid rocky body.
It has no atmosphere.
Due to this, Mercury alternates, between baking and freezing.
The surface temperature of mercury, varies from, about minus 170 degree Celsius,
during night time, to 430 degree Celsius, during day time.
Venus.
Venus is named after the Roman goddess of love and beauty.
In Hindu astrology, it was called as velli, meaning clear and pure.
It is the second planet, from the Sun, after Mercury.
It orbits the Sun, at a distance of about 108 million km.
Venus is a neighbouring planet, to Earth.
Venus is also very close to the size of our planet Earth.
It is sometimes called as the sister planet of Earth.
It has a radius, of about 6000 km.
It orbits the Sun, once in about 225 days.
Venus is a terrestrial planet.
It has a rocky composition.
The surface of Venus is a dry desertscape.
Venus has a dense atmosphere.
Among the four terrestrial planets, Venus has the densest atmosphere.
96% of the atmosphere of Venus, comprises of carbon dioxide.
The atmospheric pressure, on the surface of Venus,
is about 92 times that of Earth’s.
Venus is the hottest planet in the solar system.
The carbon dioxide, in the atmosphere creates a strong green house effect.
Venus, has a mean surface temperature of about 460 degree Celsius.
Even though our sister planet, the conditions are not conducive to life.
Earth.
The planet next to Venus, is Earth.
Earth is the third planet from the Sun.
Earth is about 150 million kilometers from the Sun.
This distance is also called as one astronomical unit.
It is a convenient measure to express large distances, in the solar system.
For example, we can say that neptune is about thirty astronomical units,
from the Sun.
This means that Neptune is thirty times more distant, from the Sun,
compared to Earth.
Earth has a radius, of about 6400 km.
It’s circumference is about 40000 km.
Earth orbits the Sun, in about 365.25 days.
This corresponds to 1 Earth year.
Earth is in the goldilocks zone of the solar system.
It is the only planet, known to sustain life.
Mars.
Mars is the fourth planet, from the Sun.
It is our neighbouring planet.
Earth has Venus on one side, and Mars on the other side, as neighbours.
Mars is the last of the four terrestrial planets.
Mars is named after the Roman god of war.
In Hindu astrology, this planet, was called as Mangala.
Mars orbits the Sun, at a distance of about 230 million km.
Mars orbits the Earth, once in about 1.9 Earth years.
Your age for example, will be about half, in Mar’s years.
Mars is smaller than planet Earth.
It has a radius of about 3400 km.
About 6 Mars size planets, can fit into Earth.
Mars is the most explored planet.
Many missions from Earth have visited Mars.
Some of the satellites, are orbiting Mars.
India has sent a satellite, which is currently orbiting Mars.
It is called MOM.
It stands for Mars Orbiter Mission.
Some missions have safely landed in Mars.
The Mars rover, called curiosity, sent by NASA,
is currently travelling, on the surface of Mars.
It is conducting experiments, of the nature of Mars.
It is controlled from Earth.
Compared to other planets, we have a much better understanding of Mars.
Mars has a solid surface, like other terrestrial planets.
Mars has volcanoes, valleys, deserts, and polar ice caps, like Earth.
Like Earth, Mars has, a mainly silicate mantle.
Mars is also known to have compounds,
of silicon, oxygen, iron, nickel, sulphur, magnesium, sodium,
potassium, chlorine, etc,.
Mars has polar ice caps.
This ice is mostly water ice.
Part of it is frozen carbon dioxide.
Mars has a very thin atmosphere.
96% of this atmosphere is carbon dioxide.
The atmosphere of Mars is quite dusty.
The temperature, in the surface of Mars, varies from about,
minus 140 degree Celsius in the polar caps,
to about 35 degree Celsius at the equator.
It was once believed, that Mars was populated, by intelligent Martians.
Many articles were written, and movies made with this theme.
Now we know that there are no intelligent Martians.
But scientists are still probing to see, whether microbial life exists in Mars.
Jupiter.
Jupiter is the 5th planet from the Sun.
Jupiter is named after the Roman king of gods.
Brahaspati, the guru of Hindu gods, is the name for the planet, Jupiter.
Jupiter orbits the Sun, at a distance, of about 780 million km.
It takes about 12 years, for Jupiter to orbit the Sun once.
Jupiter’s 12 year orbital period, corresponds to the 12 astrological signs,
of the zodiac.
Jupiter is the largest planet, in the solar system.
It has a radius of about 71500 km.
Jupiter is so large, that more than 1300 Earth size planets can fit into it.
The mass of Jupiter, is about 2.5 times, the combined mass,
of all other planets, in the solar system.
The first four planets of the solar system, Mercury, Venus, Earth, and Mars,
are terrestrial planets.
Jupiter is the first of the four gas giants.
Jupiter comprises, mostly of hydrogen and helium.
It has a surface temperature, of about 70 degree Celsius.
Unlike terrestrial planets, it lacks a well defined solid surface.
Jupiter has the largest number of moons, among all the planets.
It has 67 moons.
Galileo was able to spot, four of Jupiter’s moons, using his telescope.
Ganymede is the largest moon of Jupiter.
This moon is so big, that it is larger than the planet Mercury.
Many manmade satellites have flown past Jupiter.
They have sent back, valuable data and images.
Saturn.
Saturn is the sixth planet from the Sun.
It is named after the Roman god of agriculture.
Saturn is a gas giant.
Saturn orbits the Sun, at a distance of about 1.5 billion km.
It orbits the Sun, once in about 29 Earth years.
After Jupiter, Saturn is the second largest planet, in the solar system.
It has a radius of about 60000 km.
Saturn is so large, that about 760 Earth size planets, can fit into it.
Saturn has probably a solid core.
This core is surrounded by metallic hydrogen.
Hydrogen under very heavy pressure, is believed to exist as metallic hydrogen.
This layer is surrounded by a layer of liquid hydrogen and helium.
The outer layers are gaseous.
Most of the outer layer comprises of hydrogen and helium.
Saturn is well known for its rings.
The rings orbiting Saturn are mostly, comprised of water ice and dust.
Saturn has the most prominent ring system in the planet.
Saturn has about 150 moons.
Titan is the largest moon of Saturn.
Uranus.
Uranus is the seventh planet from the Sun.
Uranus is named after the Greek god, of the sky.
Uranus is a gas giant.
It is more specifically referred to as an ice giant.
Uranus is about 2.9 billion Kilometers, from the Sun.
It orbits the Sun, once in about 84 years.
Uranus has a radius of about 25600 km.
About 63 Earth size planets, can fit into Uranus.
The atmosphere of Uranus, mostly contain hydrogen and helium.
It has the coldest atmosphere, in the solar system.
The minimum temperature, is around minus 220 degree Celsius.
Water, ammonia, methane, are in the ice form, in Uranus.
This is the reason, that scientists call it as an ice giant.
Neptune.
Neptune is the eighth, and the last planet, in the solar system.
It is named after the Roman god of the sea.
Neptune is a gas giant.
It is more specifically referred to as an ice giant.
Neptune is about 4.5 billion Kilometers from the Sun.
It orbits the Sun, once in about 165 years.
It has a radius of about 25000 km.
About 58 Earth size planets, can fit into Neptune.
The first planet Mercury, orbits the Earth, once in about 88 days.
The last planet Neptune, takes 165 years, to complete one orbit, of the Sun.
The first planet Mercury, is about 57 million Kilometers from the Sun.
The last planet Neptune, is about 4.5 billion Kilometers from the Sun.
This gives us some idea, of the large scale of the Solar System.
Neptune’s atmosphere is composed primarily of hydrogen and helium.
Water, ammonia, and methane, is in ice form.
Scientists refer to it as an ice giant.
Temperature in the atmosphere can be as low, as about minus 220 degree Celsius.
Earth’s orbit.
Like other planets, Earth has a elliptical orbit, around the Sun.
The furthest distance of a planet’s orbit, from the Sun, is called as the Aphelion.
The Aphelion of the Earth’s orbit, is about 151.93 million km.
The closest distance of a planet’s orbit, from the Sun, is called as the Perihelion.
The Perihelion of the Earth’s orbit, is about 149.6 million km.
It takes the Earth, 365.256 days to orbit the Sun.
This defines one Earth year.
Earth’s rotation.
The Earth also rotates, on it’s own axis.
It completes one rotation, on it’s axis, once in 24 hours.
This defines a day in Earth.
When a place on Earth faces the Sun, that place experiences, day time.
When a place on Earth, faces away from the Sun,
that place experiences night time.
Earth’s axial tilt.
The axis of the Earth, is tilted relative to the Sun.
It is tilted at an angle, of about 23.5 degrees, relative to the Sun.
Due to this tilt, when the Earth orbits the Sun, places in different latitudes,
receive differential sunlight.
For half the Earth’s orbit, around the Sun, the northern hemisphere faces the Sun.
This happens from around March 20th, to around September 22nd.
During this period, the northern hemisphere experiences summer.
During this same period, the southern hemisphere experiences winter.
The maximum tilt occurs around June 21st.
The time of the maximum tilt, is called as the solstice.
In the northern hemisphere, this day, has the longest daytime of the year.
For the other half of the Earth’s orbit, around the Sun,
the southern hemisphere faces the Sun.
During this period, the southern hemisphere experiences summer.
During the same period, the northern hemisphere experiences winter.
The maximum tilt occurs around December 21st.
At two instances, in the Earth’s orbit,
the Sun is directly overhead at the equator.
This time is called as the equinox.
This happens around March 20th and September 22nd.
During the equinox, the length of the day, and night are equal.
The axial tilt of the Earth, is responsible, for the seasons, on Earth.
The relative exposure to Sunlight changes continuously during the year.
These seasons repeat, in a cyclical way, every year.
These seasons have an impact on all life forms, including our life style.
Agriculture also adapts to the seasons, in the Earth.
Geological timescale.
The Earth has been continuously evolving, since its formation,
about 4.5 billion years ago.
Scientists use a timescale to identify different time periods, in this evolution.
The largest division is called as the eon.
An eon is divided into many eras.
An era is divided into many periods.
A period is divided into many epoch.
An epoch is divided into many ages.
The last of the four eons is called as the Phanerozoic eon.
The last era, in the Phanerozoic eon, is called as Cenozoic era.
The Cenozoic era is about 66 million years old.
The most recent period, in the cenozoic era, is the Quaternary period.
The Quaternary period is about 2.6 million years old.
The most recent epoch in the Quaternary period, is the Holocene epoch.
The Holocene epoch is about 12000 years old.
We are currently living in the Holocene epoch.
The Earth was not always like, what it is now.
It evolved to this stage, over millions and billions of years.
Current structure of the Earth.
The Earth, in it’s current form, has many layers.
The inner most layer is called, as the inner core.
The next layer is the outer core.
The next layer is the mantle.
The next layer is the lithosphere.
The outer most layer is the crust.
Inner core.
The inner most core of the Earth, is a solid ball.
It has a radius of about 1200 km.
It is believed that this solid inner core, is comprised primarily of an iron-nickel alloy.
The temperature in the inner core, is about 5400 degree centigrade.
Outer core.
An outer core, surrounds the inner core of Earth.
The outer core is liquid.
The outer core is about 2300 km thick.
The outer core, is about 2900 km, below the Earth’s surface.
We will be surprised to know, that a significant portion, of the Earth,
is in a liquid state.
The outer core, is primarily comprised of molten iron and nickel.
Mantle.
The mantle of the Earth, is partly solid, and partly plastic.
The upper mantle is relatively more solid.
The lower mantle is more plastic.
The lower mantle is under higher pressure, and is more viscous.
Some portion of the mantle, comprise of molten rock.
This is called as Magma.
Volcanos exist on the surface of the Earth.
When a volcano erupts, Magma escapes from the mantle,
and the liquid Magma, flows out.
We call the Magma that flows out, as Lava.
Lithosphere.
The Earth’s lithosphere comprises of the crust, and the upper most mantle.
It is the hard and rigid layer of the Earth.
The lithosphere is divided into tectonic plates.
Crust.
The outer most layer of the Earth, is called the crust.
The crust comprises of primarily solid rocks.
The main type of rocks, in the crust are:
Igneous rocks.
Metamorphic rocks.
Sedimentary rocks.
Igneous rocks are formed through the cooling and solidification,
of magma or lava.
Metamorphic rocks, are igneous or sedimentary rocks that change in form,
due to high temperature and pressure.
Sedimentary rocks are deposited on the Earth’s surface.
It is caused by weathering and erosion of existing rocks.
The sediments are carried by water, wind, or glaciers,
and deposited in another place.
More than 90% of the Earth’s crust comprises of igneous and metamorphic rocks.
Tectonics.
The Earth is covered, by a relatively thin crust.
The crust of the Earth, can be compared to the skin of an apple.
Contrary to the general impression, of a solid Earth,
we live on a fairly thin crust, of the outer most layer of the Earth.
The crust of the Earth, is not a single shell.
It comprises of a mosaic of several rigid segments called tectonic plates.
These tectonic plates float, on a layer of dense molten rock below.
Over geologically long periods of time, these tectonics plates move around.
We would be surprised to know that the Earth was at one time,
a single super continent.
This super continent, which existed about 200 million years ago,
was called Pangaea.
This super continent broke up into a northern land mass, called Laurasia,
and a southern land mass, called Gondwanaland.
About 100 million years ago, India along with Australia, and Antarctica,
was part of Gondwanaland, close to the south pole.
The tectonic plates later broke up, and started drifting.
India for example, drifted all the way up, and collided with the Eurasian plate,
about 30 million years ago.
The force of this collision, is what caused the Himalayan range to form.
In fact the formation of all mountain ranges,
is due to drifting and collision of tectonic plates.
Eventually the tectonic plates arranged themselves,
in the current structure of the Earth.
There are currently 6 major plates.
They are:
Eurasian plate.
The American plate.
The African plate.
The Pacific plate.
The Indian plate.
The Antarctic plate.
The current continents, and the oceans are located on these plates.
In the current configuration, the continents of the Earth are:
Asia.
Africa.
North America.
South America.
Antarctica.
Europe.
Australia.
The plates continue to drift.
It happens very very slowly.
It is only over large geological periods of time, that significant changes takes place.
The occurrences of Earth quakes, however, are reminders,
that the Earth’s lithosphere, is a floating body.
The rearrangement of the plates took place over millions of years.
Compared to these geological time scales,
the appearance of we, the homo sapiens are relatively recent.
The homo sapiens originated in Africa, only about 200 thousand years ago.
It is believed that some of them migrated out of Africa,
60000 years ago, and populated the other continents.
Earth’s magnetic field.
The Earth has a magnetic field.
The magnetic field, has a north pole, and a south pole.
The magnetic poles, corresponds roughly with the geographical poles,
of the Earth.
A magnet in a compass, will align itself, with the magnetic north-south direction.
Many navigation systems, were based on the compass.
It is possible, that many birds, navigate long distances,
by sensing the magnetic field, of the Earth.
The inner core of the Earth comprises of a solid iron ball.
This is surrounded by semi liquid materials, of the outer core.
The semi liquid material flows, in a continuous current, around the inner core.
This creates a dynamo effect.
This dynamo effect, is responsible, for the magnetic field of the Earth.
This magnetic field, is constantly felt throughout the Earth.
Hydrosphere.
More than 70% of the Earth, is covered by oceans.
These oceans also, rest on tectonic plates.
The major oceans on Earth are:
The Pacific ocean.
The Atlantic ocean.
The Indian ocean.
The Arctic ocean.
The oceans constitute the hydrosphere of the Earth.
These oceans, also rest on tectonic plates.
The tectonic plates, form the floor of the ocean.
These plates are at a lower level than the continental plates.
This has helped to form, huge natural reservoirs.
The oceans fill these reservoirs.
Oceans have a strong relationship, with life forms, on Earth.
The hydrosphere is closely related to the biosphere.
Water is essential to many forms of life.
There is a continuous exchange of water, between the oceans and the continents.
Sunlight causes some of the water, in the oceans, to warm up and evaporate.
This water vapour, is present in the atmosphere.
Air currents carry this water vapour, over the land mass.
This water vapour condenses, and precipitates as snow and rain.
The water from snow and rain, flows into rivers.
The rivers flow into the sea.
This way the water from the oceans return to the sea.
This is called as the water cycle.
The water cycle plays an important role, in many forms of life.
Water is essential for human beings.
Agriculture, which produces food for human beings,
is also dependent on the water cycle.
Atmosphere.
The Earth is surrounded, by the atmosphere.
The atmosphere contains, oxygen.
Oxygen is essential for many forms of life.
The atmosphere also contains nitrogen and other gases.
The nitrogen in the atmosphere, is absorbed by the soil.
Through plants, this nitrogen finds it’s way, into our food.
The atmosphere in this way, is closely related to the biosphere.
The atmosphere plays a role, in regulating the temperature of Earth.
The temperature in many planets, fluctuate dramatically between day and night.
For example, the surface temperature of mercury,
varies from, about minus 170 degree Celsius, to 430 degree Celsius.
Thanks to the atmosphere, the day and night temperatures,
on Earth or very moderate.
This is one of the reasons that the Earth, is conducive for life.
The atmosphere extends, for hundreds of kilometres above the Earth.
Scientists have classified, the different layers of atmosphere.
There is no definite boundary, between the layers.
Just like latitudes and longitudes, these imaginary layers,
help to understand the atmosphere.
The ranges given below are approximate.
From the surface, to a height of 12 km is called the troposphere .
From 12 to 50 km, is called the stratosphere.
From 50 to 85 km, is called the mesosphere.
From 85 to 675 km, is called the thermosphere.
Above that, is called the exosphere.
The lithosphere, the hydrosphere, the atmosphere,
and the biosphere, are closely interrelated.
Moon.
The Moon is a natural satellite of the Earth.
The Moon orbits the Earth.
It is believed that the Moon broke away, from Earth,
sometime in the distant past.
The Moon orbits the Earth, effectively in a period of about 29.5 days.
Calendars of early civilisations, were based on this cycle.
This was called as the Lunar month.
The Moon has a radius of about 1700 km.
It is very much smaller compared to Earth.
It is even smaller, relative to the Sun.
When we view it from Earth, the Moon looks as big as the Sun.
This is because the Moon is relatively, much closer to Earth.
The Moon orbits the Earth at a distance of about 380000 km.
The Moon has been for a long time, part of fairy tales.
”Asking for the Moon”, was an expression used to ask, for something impossible.
This so called impossible feat,
was achieved when man landed on the Moon, in 1969.
Since then, many manned and unmanned missions have reached the Moon.
India has also successfully sent an unmanned mission to the Moon.
More missions to the Moon, are being planned.
Dwarf planets.
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune,
are the 8 major planets in the solar system.
Earlier Pluto was also considered as a planet.
Scientists later discovered more planets, comparable to the size of Pluto.
They called them dwarf planets.
Recently, Pluto was also demoted, to a status of a dwarf planet.
Currently, five planets, are recognised as dwarf planets.
They are:
Ceres.
Pluto.
Haumea.
Makemake.
Eris.
Many more dwarf planets are likely to be discovered, and recognised.
Apart from planets, millions of smaller objects, orbit the Sun.
These objects, smaller than dwarf planets, are considered as minor planets.
Asteroid belt.
Between the orbits of Earth, and the orbit of Jupiter,
there is a belt, called as the asteroid belt.
The asteroid belt, is situated roughly between the orbital distance,
of Earth and Jupiter.
Millions of minor planets, orbit the Sun, in this belt.
The size of these objects can vary, from very small dust sized objects,
to objects many hundred kilometers in diameter.
They are also called as asteroids.
Ceres is the only dwarf planet, in the asteroid belt.
It has a diameter of about 950 km.
All the other asteroids are rocky objects, of a smaller size.
Meteors.
Some of the objects, which orbit the Sun, reach Earth.
They are called meteoroids.
When a meteoroid enters the Earth’s atmosphere, it heats up.
It is then called as a meteor.
Most of the meteor, burns up while passing through the Earth’s atmosphere.
The path of a burning meteor, can be seen as a glowing streak of light.
This is sometimes called by laymen, as shooting stars.
Any left over piece of rock, which survives the journey, through the atmosphere,
and reaches the Earth, is called as a meteorite.
Typically most of them will be small pieces of rock.
The Earth is constantly bombarded by meteors.
This is more pronounced at certain periods of time.
They are referred to as meteor showers.
Kuiper belt.
The last planet in the solar system, is Neptune.
The solar system does not end here.
There are millions of more objects, orbiting the Earth,
at much larger distances.
There is a concentration, of such objects,
at a distance of 30 to 50 astronomical units, from the Sun.
An astronomical unit is about 150 million km.
This belt is called as the Kuiper belt.
The Kuiper belt, is much wider than the asteroid belt.
Millions of icy objects orbit the Earth, in this belt.
The largest object in the Kuiper belt, is Pluto.
Pluto is now designated as a dwarf planet.
Makemake is another dwarf planet, located in the Kuiper belt.
Nasa sent a mission, called New Horizon to explore Pluto,
and other objects, in the Kuiper belt, and beyond.
This journey took New Horizon, 9 years to reach the Kuiper belt.
The New Horizon mission, is still in operation.
We are likely to make more exciting discoveries, in the near future.
Comet.
Comets are objects, of rock, ice, dust and frozen gases.
Comets have a very eccentric orbit.
Some of them originate, from as far as the Kuiper belt, and beyond.
During the orbit, they come quite close to the Sun.
This causes the ice and frozen gases to evaporate.
Dust and gases form a long tail, behind the comet.
Comets have a wide range of orbits.
Their orbital periods, can vary from a few years to millions of years.
The tail of the comet, can be very long.
Some comets have tails, which are millions of kilometers long.
This makes some comets visible, to the naked eye,
when their orbits bring them closer to the Sun.
Early astronomers have observed, and recorded the appearance of comets.
Oort cloud.
The Kuiper belt, is not the end of the solar system.
There are trillions of more objects, orbiting the Sun.
There is a massive spherical cloud, enveloping the entire solar system.
This cloud extends from about 5000 astronomical units,
to about 100000 astronomical units, from the Sun.
There are trillions of icy objects, orbiting the Sun, in the Oort cloud.
The nearest star to Earth, is Proxima Centauri.
The Oort cloud is situated, about half way, to Proxima Centauri.
It is only now, we can say we have come to the end of the Solar system.