Introduction Geography is made up of two Latin words geo and graphy. Techniques in Geography Geo means “Earth” and graphy means “to describe”. Thus the general meaning of geography is the branch of science Important techniques used for the geographic enquiry are which explains about the Earth. the following: Greek scholar Haecetus has been regarded as “father of 1. Cartography: It is the science and art of drawing maps geography”. Another Greek scholar Eratosthenes first coined and charts. the term geography. He wrote the book Geography. Alexander 2. Mathematical Geography: It is closely related to the Von Humboldt and Carl Ritter are known as “founders of making of maps and interpretation and analysis of modern geography”. statistical data. 3. Remote Sensing and Geographic Information System (GIS): Remote Sensing and GIS have emerged as the most important and powerful technique for the study of geographic problems. The Universe l The universe contains billions of stars, planets, asteroids, l The Moon, for example, is a satellite of the Earth. It moves comets, meteors, solid and gaseous particles, which are around the Earth and also around the Sun along with the called celestial bodies. Earth. K l Meteors: Small pieces of space debris (usually parts of Celestial Bodies comets or asteroids) that are on a collision course with the l Nebula: It is a diffused mass of interstellar dust or gas or Earth are called meteoroids. When meteoroids enter the both, visible as luminous patches or areas of darkness Earth’s atmosphere they are called meteors or colloquially depending on the way the mass absorbs or reflects a shooting star or falling star. incident radiation. l Comets: Comets are the most exciting of the heavenly l Galaxy: The universe contains over 100 billion galaxies. A bodies. They are made up of loose collections of ice, galaxy is a group of billions of stars. Our own galaxy is dust, and small rocky particles. A well developed comet called the Milky Way, and it contains about 300 billion has a tail which is always turned away from the Sun. The stars (300,000,000,000) and one of these is our Sun. head forms the bright portion of the comet. Halley’s Comet (Markenian-348:KUNDAN Largest known galaxy. It is 13 times larger is one of the important comets. It visits the Earth regularly than Milky Way.) and is visible once in 76 years. It was last seen in 1986. l Constellation: Constellations are clusters of stars which l As comets approach the Sun, they develop enormous appear in a specific form. Centaurus, Gemini, Leo, Hercules tails of luminous material that extend for millions of and Virgo are major constellations. kilometres from the head, away from the Sun. l Stars: Some celestial bodies that have their own heat and l Asteroids: Between the orbits of Mars and Jupiter, there light are called stars. The Sun is also a star. is a swarm of small bodies which also revolve round the l The brightest star is Sirius, also called Dog Star, and the Sun. They are called asteroids. closest to the Earth is Proxima Centauri. l Stars are made up of vast clouds of hydrogen and helium Our Solar System gas and dust. Planets and other objects go round the Sun, and these make l Planets: Some celestial bodies do not have their own heat up the solar system, with the Sun at the centre. and light. These are called planets. The word planet means The solar system contains different types of objects ‘wanderer’. including: l Satellites: The word satellite means a smaller companion l a star — the Sun to anything. True to their meaning, these satellites revolve around their planets and also follow them in their revolution l planets, which go around the Sun around the Sun. l satellites, which go around the planets Geography l 1 The Sun Planets of the Sun l The Sun is 109 times bigger than the Earth and weighs There are eight planets of the Sun which revolve round it in 2 × 1027 tons. their certain orbits. l The core of the Sun has a temperature of about 15 million 1. Mercury 2. Venus 3. Earth 4. Mars degrees C. 5. Jupiter 6. Saturn 7. Uranus 8. Neptune l Sunlight takes 8 min 16.6 sec to reach Earth. Planets are classified into the following two groups — l The density of the Sun is ¼ of that of the Earth. inner and outer planets: l In its composition, 71% hydrogen and 26.5% of helium Inner Planets: Mercury, Venus, Earth & Mars are found. Outer Planets: Jupiter, Saturn, Uranus & Neptune l The Sun is about 150 million km away from the Earth. Note: The first four planets, Mercury, Venus, Earth and l Light travels with a tremendous speed of about 3,00,000 Mars are called the terrestrial planets, because of their kilometres per second. Even at this speed the Sun rays take similarity to the Earth. about eight minutes to reach the Earth. Planets l The source of energy of the Sun is nuclear fusion, in which According to distance from Sun in ascending order: small nuclei of hydrogen atom fuse into helium atom. â Mercury - Venus - Earth - Mars - Jupiter - Saturn - Uranus Different Layers of the Sun - Neptune Heat and energy are emitted from the surface of the Sun According to size in descending order: constantly. This energy is the basis for the life on the Earth’s â Jupiter - Saturn - Uranus - Neptune - Earth - Venus - Mars surface. There is 6000 degrees Centigrade temperature found - Mercury on the surface of the Sun, while it is 15 million degrees Revolves around the Sun in minimum time period: Centigrade at the core. â Venus: 225 days The central part of the Sun is known as the core. â Mercury: 88 days l The Photosphere is the “light sphere”. The dark patches Revolves around the Sun in maximum time period: on it are known as sunspots. â Pluto: 248 years l The Chromosphere (colour sphere) is the next layer. It â Neptune: 164 years Kcontains most of the “elements” found on Earth, but they are in a state of vapour. The Solar Prominences (red flames) Description of Different Planets rise high above the Chromosphere. 1. Mercury l The Corona (crown) lies beyond the Chromosphere. It l The nearest planet of the Sun, it is situated 5.7 million extends in all directions from the Chromosphere out to kilometres away from the Sun. distances of million kilometres or more. It looks like a halo l It is the smallest planet of our Solar System whose diameter completely surrounding the Sun. is only 4849.6 kilometres. l There is no atmosphere; hence there is no possibility of The Planets life. TheKUNDAN 2006 redefinition of “Planet” by the International l It has no satellite. It revolves around the Sun in 88 days. Astronomical Union (IAU) states that, in the Solar System, a 2. Venus planet is a celestial body that: l It is the brightest of all planets because it reflects more of l is in an orbit around the Sun. the Sun’s light which falls upon it than other planets do. l has sufficient mass so that it assumes a hydrostatic l Clouds of sulphuric acid are found here. equilibrium shape. l It is the nearest planet to the Earth. l has “cleared the neighbourhood” around its orbit. l It is similar to the Earth in volume, weight and density; A "dwarf planet" is a celestial body that (a) is in orbit therefore, it is called sister of the Earth and twin star. It is around the Sun, (b) has sufficient mass for its self-gravity to also known as Evening Star and Morning Star. overcome rigid body forces so that it assumes a hydrostatic l The cloud sphere of Venus is of orange colour, therefore it equilibrium (nearly round) shape, (c) has not cleared the is known as the orange planet. neighbourhood around its orbit, and (d) is not a satellite. l It rotates from east to west while the Earth rotates from According to this definition, there are currently eight west to east. planets and five dwarf planets known in the Solar System. l It has no satellite or moon. The five dwarf planets are Pluto, Ceres, Eris, Makemake and Haumea. 3. Earth l According to distance, it is third from the Sun. It is the fifth largest planet. It is 148.8 million km away from the Sun. 2 l Geography l It rotates along its own axis in 24 hours. in a complete revolution, it comes closest to the Earth l It revolves around the Sun in 365 days 5 hours and 42 twice and goes the farthest twice. minutes. l The nearest position of the Moon to the Earth is known as l It is called the Blue Planet. perigee and the farthest position is known as apogee. l It is the only planet where life exists due to favourable When the Earth, the Sun and the Moon are collinear, it is atmosphere. known as syzgie. l Its diameter is 12,733.2 kilometres. Solar Eclipse and Lunar Eclipse l It has only one satellite — the moon. l When the Earth comes between the Sun and the Moon, l It is tilted at 23½ degrees on its axis and thus makes an the Moon is unable to get sunlight, i.e. the Moon is angle of 66½ degrees. partially or fully over-shadowed. This is called the lunar l It takes 23 hours, 56 minutes and 4 seconds to rotate once eclipse.