The Universe:

Physical geography is the study of the universe and physical landscape. The pioneering work of physical geography was initiated by Greek geographer Eratosthenes who accurately calculated the circumference of earth based on observation of angle of sun on different places of Egypt. Eratosthenes is also credited for postulating the spherical shape of earth and drawing maps of earth’s environmental zones.

Physical geography is multifaceted discipline that seeks to explore physical features of the universe. Physical geographical geographers have devised systems and models to study physical phenomena. Each of these systems and models may have sub units. Such classification of physical world helps to understand complexity and diversity of universe. The study of universe remains at the core of physical geography.

     The universe can be defined as the entity that comprises of all the matter and energy that is unevenly distributed in time and space. It is the reservoir of enormous energy and innumerable cosmic objects. The most visible objects in the universe are stars that have their own light. In the open sky we may observe the bright patches of light that are actually clusters of millions of stars. Such cluster of stars is known as galaxy. Galaxies are at great distances from each other. In order to measure distances of galaxies we use the unit of light year which is distance covered by light in one year.   

    Solar system is the system of sun and its planets and moons. The solar system belongs to Milky-Way galaxy. Milky Way galaxy is spiral in shape and contain extremely bright and very dense central core around which it is spinning. Milky Way galaxy may contain 100 billion stars of which sun is medium sized star. Our solar system contains sun and nine planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. Mercury is closest to sun and Pluto the farthest. Jupiter is greatest planet while Pluto the smallest. Due to its distance from the rest of planets and small size the scientists sometimes do not include it with the planets. All these planets are revolving round the sun in concentric orbits. Pluto has its own elliptical orbit. One complete circling of sun is called Revolution and time taken to complete one revolution is called time period. Among the planets, Mercury has the shortest time period which is 88 days while Pluto has 247.7 years. Our earth completes its revolution in one year. Of all planets contains physical atmosphere that allows life on earth. Besides these planets the solar system also comprises of moons, the satellites that orbit round the planets, asteroids, meteoroids and other celestial bodies.

  

     Regarding origin of the universe, the most widely accepted theory is Big Bang Theory. Big Bang is the name given massive explosion about 1500 billion years ago that resulted in the creation of universe. It is believed that before Big Bang all the matter and space was condensed into one infinite entity. As a result of this gigantic explosion, all the matter scattered over space and time which is cooling and slowing ever since. The rapidly expanding fireball scattered into pieces. From the debris of this primordial substance, all the contents of the universe are gradually formed. Galaxies and stars took shape from condensation and consolidation of clouds of dust. Gravity then helped these particles to cling together to form stars and planets. The sheer magnitude of explosion can be understood from the fact that that even after 1500 billions years the faint echo of the explosion still can be heard. Energy and matter is constantly being scattered in ever widening universe.