Showing posts with label Physical Geography. Show all posts
Showing posts with label Physical Geography. Show all posts

Tuesday, November 5, 2013

Solar System

planets in solar system

Solar System

The Solar System comprises the Sun and its planetary system of eight planets, their moons, and other non-stellar objects. It formed 4.6 billion years ago from the gravitational collapse of a giant molecular cloud. The vast majority of the system's mass is in the Sun, with most of the remaining mass contained in Jupiter. The four smaller inner planets, Mercury, Venus, Earth and Mars, also called the terrestrial planets, are primarily composed of rock and metal. The four outer planets, called the gas giants, are substantially more massive than the terrestrials. The two largest, Jupiter and Saturn, are composed mainly of hydrogen and helium; the two outermost planets, Uranus and Neptune, are composed largely of substances with relatively high melting points (compared with hydrogen and helium), called ices, such as water, ammonia and methane, and are often referred to separately as "ice giants". All planets have almost circular orbits that lie within a nearly flat disc called the ecliptic plane.
The Solar System also contains a number of regions populated by smaller objects.The asteroid belt, which lies between Mars and Jupiter, is similar to the terrestrial planets as it mostly contains objects composed of rock and metal. Beyond Neptune's orbit lie the Kuiper belt and scattered disc, linked populations of trans-Neptunian objects composed mostly of ices. Within these populations are several dozen to more than ten thousand objects that may be large enough to have been rounded by their own gravity. Such objects are referred to as dwarf planets. Identified dwarf planets include the asteroid Ceres and the trans-Neptunian objects Pluto, Eris , Haumea, and Makemake. In addition to these two regions, various other small-body populations includingcomets, centaurs and interplanetary dust freely travel between regions. Six of the planets, at least three of the dwarf planets, and many of the smaller bodies are orbited by natural satellites, usually termed "moons" after Earth's Moon. Each of the outer planets is encircled by planetary rings of dust and other small objects.
The solar wind, a flow of plasma from the Sun, creates a bubble in the interstellar medium known as the heliosphere, which extends out to the edge of the scattered disc. The Oort cloud, which is believed to be the source for long-period comets, may also exist at a distance roughly a thousand times further than the heliosphere. The heliopause is the point at which pressure from the solar wind is equal to the opposing pressure of interstellar wind. The Solar System is located within one of the outer arms of the Milky Way galaxy, which contains about 200 billion stars.

source : wikipedia

Friday, November 1, 2013

Weathering ?

weathering definition

what is Weathering ?

Weathering is a static process. The process of disintegration and decomposition of rocks in situ is generally called weathering.

weathering definition

Weathering refers to the breakdown or disintegration and decomposition of rocks in situ through mechanical and chemical changes in the rocks  and their minerals effected by water, temperature, wind, different atmospheric gases and organisms provided that there is no large-scale transport of weathered products by denudational processes except massmovement of rockwastes down the slope under the impact of gravity.

According to C.D. Ollier (1969), “weathering is the breakdown and alteration of minerals near the earth’s surface to products that are more in equilibrium with newly imposed physico-chemical conditions”
According to P. Reiche (1950), “weathering is the response of minerals which were in equilibrium within the lithosphere to conditions at or near its contact with the atmosphere, the hydrosphere, and perhaps still more importantly ,the biosphere.”
B. B. Polynov(1937), has very precisely defined weathering as ‘the change of rocks from the massive to the clastic state.’
According to B. W. Sparks, “weathering may be defined as the mechanical fracturing or chemical decomposition of rocks by natural agents at the surface of the earth”

Arthur Holmes has presented more elaborate definition of weathering which also includes the processes of weathering.According to him “ weathering is the total effect of all the various subaerial processes that cooperate in bringing about the decay and disintegration of rocks, provided that no large-scale transport of the loosened products is involved. the work of rainwash and  wind, which is essentially erosional, is thus excluded”
-A. Homes (1952)

It appears from the above definitions that weathering is essentially the breakdown of rocks due to chemical and mechanical processes at their places.


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