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 and what not. Despite unavoidable free objects and services provided by earth to humans we are not being able to pay off her kindness to us. It is the only that harbors life. 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.
UNIVERSE
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 occurred before the bounce, and, in a cyclic version, the universe bounces at regular intervals.
This theory received impressive success in accurately describing what we know so far about our universe. It predicts a uniform, flat universe with patterns of hot spots and cold spots now visible in the cosmic microwave background (CMB). 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 EARTH
Scientists and geologists across the world have put forth their hypotheses regarding the origin of the earth. One of the earliest scientist Kant in his 1755 work, “The Universal Natural History and Theories of the Heavens,” gave two important theories about heavens, The first is his “Nebular Hypothesis” on star and planetary formations, where he presented theory that thin, dim clouds of dust and gas out in the cosmos would collapse on themselves under the force of gravity, causing them to spin to form a disk. He further said, from this spinning disk, stars and planets would form.
Laplace modified it in 1796 by presenting Nebular Hypothesis. According to Laplace, planets were formed out of a cloud of material associated with a youthful sun, which was slowly rotating. Laplace also proved that the birth of the Earth was due to the horrific explosions occurring in the sun.
In 1900, Chamberlain and Moulton put forth that a wandering star approached the sun resulting a cigar-shaped extension of material which was separated from the solar surface. As the passing star moved away, the material separated from the solar surface continued to revolve around the sun and it slowly condensed 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 coexisting.
These views are called binary theories.
In 1950, Otto Schmidt in Russia and Carl Weizsacker in Germany slightly 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 along with dust.
In this manner, the friction and collision of particles led to formation of a disk-shaped cloud and the planets were formed through the process of accretion.
Interestingly, scientists in later period took up the problems of origin of universe rather than that of just the earth or the planets.
GALAXIES
Huge mass of stars, nebulae and stellar remnants and interstellar medium of gas dust and dark matter is called Galaxy. There are billions of galaxies in the universe. Our solar system is a part of Milky Way Galaxy. Our galaxy is called Milky Way. Galaxies are of three types – spiral galaxy, elliptical galaxy and irregular galaxy.
MILKY WAY
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 demoted to the status of dwarf planet. The order of these planets in increasing distance from the Sun is as follows: Mercury, Venus, Earth Mars, Jupiter, Saturn, Uranus and Neptune. These planets have not their own light, in fact; they receive light from the sun.
SUN
The Sun is the primary source of energy for life on Earth. It is the closest star to the Earth. The Sun is the center of solar system. It is huge and made of extremely 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 contains 99.86% of the mass in the Solar System. The Sun consists 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. Its light takes about 8 minutes to reach the earth. All the planets of the Solar System move around the Sun in an elongated fixed path called orbits.
PLANETS
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
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 no atmosphere to absorb meteor impacts, so its surface is pockmarked with craters, just like the moon. 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
Venus is a rocky planet and it is also known as a terrestrial planet. Its solid surface is a cratered and volcanic. Its thick and toxic atmosphere is made up mostly of carbon dioxide (CO2) and nitrogen (N2), with clouds of sulfuric acid (H2SO4) droplets. Venus is the brightest planet. Venus is hotter than Mercury. Its size and structure are similar to Earth. Venus spins slowly in the opposite direction of most planets. It has diameter of 12,104 km.
• It is known as Earth’s twin. It has longest rotation period of any planet. Its rotation period is longer than its orbital period. It is the hottest planet in the solar system.
• Dense atmosphere of gases and chemicals including sulphuric acid clouds. It revolves around the sun in clockwise manner while most others are revolving in anti-clockwise direction. It is second brightest natural object in the night sky (after Moon). It can be seen from the earth only before sunrise and after sunset. For it, it is called Morning Star and Evening Star.
Earth
The Earth is our home planet. It is the third planet from the Sun. it is fifth largest planet 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. Earth’s atmosphere is rich in life-sustaining nitrogen and oxygen. Earth’s surface rotates about its axis at 467 meters per second. The planet zips around the Sun at more than 18 miles per second (29 km per second). It has diameter of 12,760 km. There is water in all three states – liquid, solid and gas. Gasses present in the earth’s atmosphere are Nitrogen, Hydrogen, Oxygen, Carbon Dioxide etc. 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.
Formation of the Earth
Scientists have claimed to solve this mystery. Studying the volcanic rocks has helped them to understand the secret that the earth must be built four and a half billion years ago. Science magazine ‘Nature’ has published the research done by scientists from other European countries including the University of Edinburgh. For this, the scientists have studied basalt which was formed after the cooling of the volcanic lava. They have tried to figure out what might be the process of making the earth and its environment.
Scientists tested this basalt i.e. magma (a mixture of molten or semi-molten rocks found below the surface of the earth) at temperatures above 2000 degrees Celsius. They studied from this study that due to this molten magma, there would be sea like structure in the Earth’s mantle (the surface of the Earth and the outer core between 2900 km thick).
According to these scientists, when the earth would have been built four and a half billion years ago, most of our land would have been like wagging lava. Later as the lava became cold, the upper surface of the earth began to form. Now scientists are curious to know how the upper surface of the earth and the inner core has been shaped and how the volcanic activity begins to operate within it.
Mars
Mars is the fourth planet from the Sun. It is cold and dusty place. It is rocky, has mountains and valleys. Mars harbors water ice. Scientists are of view that the conditions of this planet may be quite suitable for existence of life. It has diameter of 6,787 Kilometers and known as the ‘Red Planet’ due to presence of iron-rich red soil. Phobos and Deimos are the two moons of Mars. It has polar ice caps and traces of sub-terrestrial liquid water have been found. It has the largest known volcano (and second tallest mountain) in the solar system – Mons Olympus.
Jupiter
The fifth planet from the sun, Jupiter is huge and is the largest planet in our solar system. It’s a mostly gaseous world, mostly hydrogen and helium. Its swirling clouds are colorful due to different types of trace gases. A big feature is the Great Red Spot, a giant storm which has raged for hundreds of years. Jupiter has a strong magnetic field, and with dozens of moons, it looks a bit like a miniature solar system. 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
The sixth planet from the sun is known most for its rings. This gaseous planet is mostly consists of hydrogen and helium. It has an average radius about nine times that of Earth. Its diameter is about 120,500 km.
It is the second largest planet in the Solar system. Its density is less than the water.It has a band of concentric rings revolving around it made up of tiny rocks and pieces of ice. It has 62 moons.
Uranus
Uranus is an oddball. It’s the only giant planet whose equator is nearly at right angles to its orbit. It basically orbits on its side. Uranus is about the same size as Neptune. It was discovered by William Herschel in 1781. Its diameter is about 51,120 km and is blue-green (cyan) in color. It is the third biggest planet of the solar system. It is composed of Hydrogen, Helium, Water, Ammonia, and Methane. It is tilted sideways so that its poles lie where most other planets have their equators. It has faints rings. It has 27 known moons. .
Neptune
Neptune is known for strong winds — sometimes faster than the speed of sound. It has a rocky core. Neptune is about 17 times as massive as 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 was demoted to status of ‘Dwarf Planet’. It is icy and rocky. It has five satellites. Pluto is unlike other planets in many respects. It is smaller than Earth’s moon. Its orbit carries it inside the orbit of Neptune and then way out beyond that orbit. From 1979 until early 1999, Pluto had actually been the eighth planet from the sun. Then, on Feb. 11, 1999, it crossed Neptune’s path and once again became the solar system’s most distant planet — until it was demoted to dwarf planet status. Its diameter is 1,430 2,301 km.
Planet Nine
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 a number of strange features of our solar system that are best explained by the presence of a ninth planet. Planet Nine orbits the Sun at a distance that is 20 times farther out than the orbit of Neptune. (The orbit of Neptune is 2.7 billion miles from the sun at its closest point.) 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. Its existence was inferred by its gravitational effects on other objects in the Kuiper Belt, a region at the fringe of the solar system that is home to icy objects left over from the birth of the sun and planets.
ASTEROIDS
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 in the Solar System.
METEORITES
Meteoroids are formed due to the collisions between asteroids. They are fragments of rocks floating about in space. Sometimes they come across the earth and fall into the earth’s atmosphere. That’s when they become meteors or “shooting stars”. Most of these meteors can’t reach earth’s surface and burn up in the atmosphere due to the friction with air. The meteors that reach the earth’s surface are known as meteorites.
COMETS
Tiny icy and rocky bodies that travel in highly elliptical orbits around the sun. When they pass close to the sun, they water and gases heat up. This leads to the formation of a tail behind the rocky core in the direction opposite to the Sun. Most famous comet is Halley’s Comet which reappears every 75-76 years. It was last appeared in 1986 and next appearance is expected in 2061.
CONSTELLATIONS
Various patterns formed by different groups of stars are called constellation. Big bear is an example.
SATELLITES
Satellites are celestial bodies that move around the planets. Human has also made several artificial satellites. Satellite orbits a planet or star. Earth is a satellite because it orbits the sun. Likewise, the moon is a satellite because it orbits Earth.
Artificial “satellite” refers to a machine that is launched into space and moves around Earth or another body in space.
Earth and the moon are examples of natural satellites. Thousands of artificial, or man-made, satellites orbit Earth. Some take pictures of the planet that help meteorologists predict weather and track hurricanes. Some take pictures of other planets, the sun, black holes, dark matter or faraway galaxies. 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
Moon is the only satellite of the Earth. Its diameter is one quarter that of earth. It is about 3,84,4000 km away from the earth. It takes about 27 days to revolve around the earth and about the same time to rotate and its own axis. As a result only one side of the moon is visible to us on the earth. It is the second brightest object in the sky after the Sun. As the Moon orbits around the Earth once in a month, the angle between the Earth, the Moon and Sun changes. It is called the cycle of the Moon’s phases. The time between successive new moons is 29.5 days (709 hours), slightly different from the Moon’s orbital period (measured against the stars) since the Earth moves a significant distance in its orbit around the Sun in that time. Due to its size and composition, the Moon is sometimes referred as a terrestrial planet.
Quick Facts about planets
Largest-/ Biggest Planet Jupiter
Smallest Planet Mercury
Satellites of Earth Moon
Nearest planet to the Sun Mercury
Earth’s twin Venus
Brightest Planet Venus
Brightest Star Ceres
Planets with rings around Saturn
Red Planet Mars
Blue Planet Earth
Green Planet Neptune