Earth is a beautiful living planet of the Universe as the common habitat of more than 7.6 billion human population and millions of species of biodiversity. Our Earth provides us with food, shelter, medicine, water and what not. The story of the emergence of the earth is very old and strange and scholars of the world have presented the story of the birth of earth in different ways propounding their own theories. Before knowing about the earth we need to know about the universe, which is infinite and unlimited in time and space.
The most popular and accepted theory regarding the origin of the universe is the Big Bang Theory. This theory is also called expanding universe hypothesis.
Edwin Hubble (November 20, 1889-September 28, 1953), an American astronomer, in 1920, provided evidence that the universe is expanding. He was of the view that as time passes, galaxies move further and further apart. According to Edwin Hubble everything in the universe emerged from a point known as singularity, about 13.7 billion years ago.
In 2001, ekpyrotic universe theory was introduced by Burt Ovrut, Justin Khoury, Paul Steinhardt and Neil Turok. In this theory, these scholars propounded this cosmological model of the early universe explaining the origin of the structure of the cosmos. This theory also answers the questions arising in the scholars about what happened before the Bing Bang. According to this theory, Bing Bang was a big bounce, a transition from a previous epoch of contraction to the present epoch of expansion. These scholars are of the view that the major events that shaped our universe took place earlier than the bounce.
This theory received impressive success in accurately describing what we know so far about our universe. According to this theory universe is a uniform, flat universe having patterns of hot spots and cold spots visible in the cosmic microwave background. Discovery of the cosmic microwave background was considered a landmark test of the big bang, but according to proponents of the ekpyrotic and cyclic theories, the CMB is also consistent with a big bounce.
Scientists and geologists across the world have put forth their hypotheses regarding the origin of the earth. One of the earliest scientists Kant in his 1755 work, “The Universal Natural History and Theories of the Heavens,” gave two important theories about heavens; the first is Kant’s “Nebular Hypothesis” on star and planetary formations. In this, he presented theory that thin, dim clouds of dust and gas out in the cosmos would collapse on themselves due to force of gravity, causing them to spin to form a disk. In his view, from this spinning disk, stars and planets would form.
Laplace modified it in 1796 by presenting Nebular Hypothesis. He opined that planets were formed out of a cloud of material associated with a slowly rotating youthful sun. Laplace also proved that the birth of the Earth was due to the horrific explosions occurring in the sun.
In 1900, Chamberlain and Moulton said that a wandering star came near to the sun resulting in a cigar-shaped extension of material that separated from the solar surface. They propounded that when the transitory star moved away, the material alienated from the solar surface kept on revolving around the sun. This material gradually reduced into planets.
Sir James Jeans and later Sir Harold Jeffrey supported this view. In fact, the arguments considered of a companion to the Sun to have been co-existing.
In 1950, Otto Schmidt in Russia and Carl Weizsacker in Germany somewhat revised the ‘nebular hypothesis’, though differing in details. They are of views that sun was surrounded by solar nebula which contained mostly the hydrogen and helium.
In fact, the friction and collision of particles formed disk-shaped cloud and the planets were formed through the process of accumulation.
Interestingly, scientists in later period took up the problems of origin of universe rather than that of just the earth or the planets.
Enormous mass of stars, nebulae and stellar remnants and interstellar medium of gas dust and dark matter is called Galaxy. Universe consists of billions of galaxies. Our solar system is an integral part of Milky Way Galaxy. Our galaxy is called Milky Way. Galaxies are of three types – spiral galaxy, elliptical galaxy and irregular galaxy.
The earth belongs to the Milky Way, which is consists of the sun, the earth, planets, satellites and other stars. Milky Way contains millions of stars including our solar system. It is estimated that Milky Way has approximately 151,000 million stars. The disk of the Milky Way has a diameter of nearly 180, 00 light years and thickness of 15,000 light years.
THE SOLAR SYSTEM
Our solar system consists of the star Sun, eight planets and a large number of satellites. Often it is called a Solar Family with the sun as its head.
Earlier there were nine planets but due to planetary definition put forth by the International Astronomical Union on 24th August, 2006 at Prague, the Pluto lost its status as a planet and was reduced to the status of dwarf planet. The distance of these planets in increasing order from the Sun is – Mercury, Venus, Earth Mars, Jupiter, Saturn, Uranus and Neptune. These planets have not their own light, in fact; they receive light from the sun.
Discovery of the cosmic microwave background was considered a landmark test of the big bang, but according to proponents of the ekpyrotic and cyclic theories, the CMB is also consistent with a big bounce.
The Sun is the major source of light and energy on the earth. It is the center of solar system. It is huge and made of very hot gases. It is estimated that one million Earths could fit inside the Sun. It possesses the strong gravity binding the entire Solar System including planets, satellites, asteroids and meteors in its orbit. Sun has a radius of 700000 km making it the largest object in the Solar System. The Sun consists of 99.86% of the mass in the Solar System. The Sun is made of 70% hydrogen, 28% Helium & 2% other gases. The temperature is about 6000 °c and it is about 150 millions Kilometers away from the earth. The light takes 8 minutes to reach the earth. All the planets of the Solar System move around the Sun in a fixed path called that is called orbits.
The eight planets in the Solar System are Mercury, Venus, Earth, Mars Jupiter Saturn, and Uranus & Neptune. The planets can be divided into two groups – a) Terrestrial Planets – Mercury, Venus earth & Mars and, b) Jovian or Outer planets – Jupiter, Saturn Uranus, and Neptune.
Mercury is the closest planet to the Sun. It is a bit larger than Earth’s moon. Its temperature can reach 450 degree Celsius, but at the night it drops to hundreds of degrees below freezing. Mercury has not any atmosphere to absorb impacts of meteor over its four-year mission, (nearest to the sun). It is the smallest planet. It is visible to the naked eyes. Its diameter is about 4,878 km. Its rotation period is longer than its orbital (revolution) period. It has no natural satellites.
Venus is a rocky planet and it is also known as a terrestrial planet. Its solid surface is volcanic. Its atmosphere is made up mostly of carbon dioxide and nitrogen, with clouds of sulfuric acid droplets. Venus is the brightest planet. Venus is hotter than Mercury. Its size and structure are similar to earth. This spins slowly in the opposite direction of most of the other planets. It has diameter of 12,104 km.
- It is known as Earth’s twin. It has the longest rotation period. Rotational period of this hottest planet is longer than its orbital period.
- It revolves around the sun in clockwise manner while most others are revolving in anti-clockwise direction. It is the second brightest object in the night sky after the Moon. Venus may be seen from the earth only before sunrise and after sunset. For it, it is called Morning Star and Evening Star.
The Earth is third planet from the Sun. It ranks fifth in size in the solar system. The Earth is the only planet in the solar system to be known to support life.
It is slightly larger than Venus. Earth is the largest planet of the terrestrial planets. Nitrogen and Oxygen are in abundance in earth. Apart from it, there are gases like Carbon Dioxide, Hydrogen etc. Earth’s surface rotates about its axis at 467 meters per second. It has diameter of 12,760 km. There is water in all three states – liquid, solid and gas. The Earth takes 23 hour 56 minutes 46 seconds to rotate around its axis. It takes 365.26 days to revolve around the Sun. The Ozone layer present in the Earth’s atmosphere protects it from the ultra violet rays coming directly from the Sun. It has one natural satellite called Moon.
Mars is the fourth planet from the Sun. It is rocky, cold and dusty and has mountains and valleys. Scientists are of view that the conditions of this planet may be quite suitable for existence of life. Its diameter is 6,787 Kilometers and it is known as the ‘Red Planet’ due to presence of iron-rich red soil. Mars has two moons- Phobos and Deimos. It has polar ice caps and traces of sub-terrestrial liquid water have been found. It has the largest known volcano in the solar system – Mons Olympus.
Jupiter is the largest and the fifth planet from the sun. It is composed of gases, mostly hydrogen and helium. Its clouds are swirling and colorful. It is due to different types of trace gases. Great Red Spot is a main feature of this planet. It is a giant storm which has raged for hundreds of years. It has a strong magnetic field and 53 moons. It is the largest planet of the solar system and has 67 satellites. It has the shortest rotation period. It has diameter of 139,822 km.
Saturn is famous for its rings and is the sixth planet from the sun. This gaseous planet is mostly consists of hydrogen and helium. Its radius is about nine times than that of Earth. Its diameter is about 120,500 km.
It is the second largest planet. Its density is less than the water. It has a band of concentric rings that revolves around it. These rings are made up of tiny rocks and pieces of ice. It has 62 moons.
Uranus is the planet equator of which is nearly at right angles to its orbit. It basically orbits on its side. William Herschel discovered in 1781. Its diameter is about 51,120 km and is blue-green (cyan) in color. It is the third largest planet. It is composed of Hydrogen, Helium, Water, Ammonia, and Methane. It is tilted sideways. That is why its poles lie where most other planets have their equators. It has faints rings. It has 27 known moons. .
Strong winds are major features of the Neptune. These winds are sometimes faster than the speed of sound. It has a rocky core. Neptune is about 17 times massive than that the Earth. It was discovered by John Couch Adams in 1946. Its diameter is 49,530 km. it was discovered by mathematical predictions and disturbances in Uranus’ orbit. It is farthest planet from the Sun. it is primarily composed of hydrogen, helium, nitrogen, water, ammonia, methane. It is blue colored due to presence of methane. It has 14 known satellites.
Pluto (Dwarf Planet)
Once the ninth planet from the Sun, the Pluto was demoted to status of ‘Dwarf Planet’. It is icy and rocky. It has five satellites. It is smaller than Earth’s moon. From 1979 to 1999, Pluto had been the eighth planet from the sun. Then, on Feb. 11, 1999, until it was demoted to dwarf planet status. Its diameter is 1,430 2,301 km.
It is newly found hypothetical planet. According to NASA, it is hard to imagine our solar system without the unseen world. This hypothetical planet is believed to be about 10 times more massive than Earth and located in the dark, outer reaches of the solar system, approximately 20 times farther from the sun than Neptune is. The mystery has yet to be revealed. Astronomers have discovered several strange features of the solar system. The strange planet’s orbit is about 600 times farther from the sun than the Earth’s orbit is from the star. Scientists have not seen Planet Nine directly.
Asteroids are almost like planets but smaller in size. They have no spherical in appearance. They revolve around the Sun. Most of them are found in a belt between the planets Mars and Jupiter. Ceres is the largest asteroid.
When collisions occurred among asteroids meteoroids are formed. Meteorites are fragments of rocks floating in space. Sometimes they come across the earth and fall into the earth’s atmosphere. Most of these meteors are unable to reach earth’s surface and burn up in the atmosphere due to the friction. This friction takes place with air. The meteors that reach the earth’s surface are known as meteorites.
Comets are small icy bodies that travel in elliptical orbits around the sun. Comets are generally rocky. When they pass close to the sun, water and gases heat up. It leads to the formation of a tail behind the rocky core. This core is in the direction opposite to the Sun.
Constellations are various pattern formed by different group of stars. In a simple language they are group or clusters of stars.
Satellites move around the planets. Human has also made several artificial satellites. Satellite orbits a planet or star. Earth revolves around the sun and it makes it a satellite. Likewise, the moon is a satellite as it revolves around the earth.
Satellites may also be artificial and they are made by man. These are launched into space and moves around Earth or another body in space.
Thousands of man-made satellites orbit Earth. Some of these satellites take pictures of the planet to help meteorologists in predicting weather and track hurricanes. These pictures assist scientists better understand the solar system and universe. Apart from it, they are used for communications, such as beaming TV signals and phone calls around the world.
Moon is the only satellite of the Earth. In term of distance, it is 3,84,4000 km away from the earth. It takes about 27 days to orbit around the earth and about the same time to rotate at its own axis. This is the reason that we can see only one side of the moon at a given time. As the Moon revolves around the earth once in a month, thus the angle between the Earth, the Moon and Sun get changed. It is called the cycle of the Moon’s phases. Due to its size and composition, the Moon is sometimes referred as a terrestrial planet.