Formation of Stars

Gravitational Forces


Solar System

The Universe

Teachers' Corner









  What is the Solar System?

The Solar System is made up of all the planets that orbit our Sun. In addition to planets, the Solar System also consists of moons, comets, asteroids, minor planets, and dust and gas. Each of these bodies is held to each other by the force of gravity.

Everything in the Solar System orbits or revolves around the Sun. The Sun contains around 98% of all the material in the Solar System. The larger an object is, the more gravity it has. Because the Sun is so large, its powerful gravity attracts all the other objects in the Solar System towards it. At the same time, these objects, which are moving very rapidly, try to fly away from the Sun, outward into the emptiness of outer space. The result of the planets trying to fly away, at the same time that the Sun is trying to pull them inward is that they become trapped half-way in between. Balanced between flying towards the Sun, and escaping into space, they spend eternity orbiting around their parent star.

The sun is by far the largest part of the solar system. The other principal members of the solar system are the nine major planets.

The planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto (which is now considered a dwarf planet). The planets orbiting nearer the sun than the earth are called inferior planets; those whose orbits are larger are called superior planets. The unit for measuring distance in the solar system is the astronomical unit (A.U.), the average distance between the earth and the sun. The mean distances of the planets from the sun range from 0.39 A.U. for Mercury to 39 A.U. for Pluto.



How Did The Solar System form?

This is an important question, and one that is difficult for scientists to understand. After all, the creation of our Solar System took place billions of years before there were any people around to witness it. Our own evolution is tied closely to the evolution of the Solar System. Thus, without understanding from where the Solar System came from, it is difficult to comprehend how mankind came to be.

Scientists believe that the Solar System evolved from a giant cloud of dust and gas. They believe that this dust and gas began to collapse under the weight of its own gravity. As it did so, the matter in this could begin moving in a giant circle, much like the water in a drain moves around the center of the drain in a circle.

At the center of this spinning cloud, a small star begin to form. This star grew larger and larger, as it collected more of the dust and gas that were collapsing into it.

Further away from the star that was forming in the center were smaller clumps of dust and gas that were also collapsing. The star in the center eventually ignited forming our Sun, while the smaller clumps became the planets, minor planets, moons, comets, and asteroids.



The Sun

The Sun is the star at the centre of the Solar System. The Earth and other matter (including other planets, asteroids, meteoroids, comets and dust) orbit the Sun, which by itself accounts for about 99.8% of the solar system's mass. Energy from the Sun—in the form of sunlight—supports almost all life on Earth via photosynthesis, and drives the Earth's climate and weather.






Mercury is the innermost and smallest planet in the solar system, orbiting the Sun once every 88 days. It can only be seen in morning or evening twilight. Comparatively little is known about the planet. Physically, Mercury is similar in appearance to the Moon as it is heavily cratered. It has no natural satellites and no substantial atmosphere. The Romans named the planet after the fleet-footed messenger god Mercury, probably for its fast apparent motion in the twilight sky.




Venus is the second-closest planet to the Sun, orbiting it every 224.7 Earth days. It is the brightest natural object in the night sky, except for the Moon. Because Venus is an inferior planet, from Earth it never appears to venture far from the Sun. Venus reaches its maximum brightness shortly before sunrise or shortly after sunset, for which reason it is often called the Morning Star or the Evening Star. The planet is named after Venus, the Roman goddess of love; most of its surface features are named after famous and mythological women.







The earth rotates or turns from west to east about a line called its axis. The period of one complete rotation is a day. Because of the rotation of the earth we experience light and darkness (day and night). The earth revolves about the sun once every 365 1/4 days which is a year. The path of this revolution, the earth's orbit, is an oval in shape. This means the earth is closer to the sun in January than it is in July.

The change in seasons is caused by the tilt of the earth on its axis. When the northern end of the earth's axis is toward the sun, the most direct rays of sunlight fall in the Northern Hemisphere. This causes its summer season. At the same time the Southern Hemisphere has winter since it is then receiving indirect rays. Halfway between, in spring and in autumn, there is a time called the equinox when all parts of the earth have equal day and night. When the northern end of the earth's axis is tilted away from the sun, the least direct sunlight falls on the Northern Hemisphere. This causes winter.




Mars is the fourth planet from the Sun and is known as the Red Planet due to its reddish appearance as seen from Earth. The planet is named after Mars, the Roman god of war. A terrestrial planet, Mars has a thin atmosphere and surface features reminiscent both of the impact craters of the Moon and the volcanoes, valleys, deserts and polar ice caps of Earth. It has the highest mountain in the solar system, Olympus Mons, and the largest canyon, Valles Marineris. Mars' rotational period and seasonal cycles are also similar to those of the Earth. Mars has two moons, Phobos and Deimos, which are small and oddly shaped. Mars can be seen from Earth with the naked eye.





Jupiter is the fifth planet from the Sun and the largest planet within the solar system. It is two and a half times as massive as all of the other planets in our solar system combined. Jupiter, along with Saturn, Uranus, and Neptune, is classified as a gas giant. Together, these four planets are sometimes referred to as the Jovian planets. The Romans named it after Jupiter, the principal God of Roman mythology, whose name is a reduction of 'Deus Pater', meaning 'God father'.



Saturn is the sixth planet from the Sun. It is a gas giant (also known as a Jovian planet, after the planet Jupiter), the second-largest planet in the Solar System after Jupiter. Saturn has a prominent system of rings, consisting mostly of ice particles with a smaller amount of rocky debris and dust. It was named after the Roman God Saturn (the Greek equivalent is Cronos, father of Zeus).








Uranus, named for the Greek word, meaning "heaven" or "sky" is the seventh planet from the Sun. It is a gas giant, the third largest by diameter and fourth largest by mass. It is named after Uranus, the Greek god of the sky and progenitor of the other gods. Uranus is the first planet discovered in modern times. Sir William Herschel formally discovered the planet on March 13, 1781; the other planets (from Mercury out to Saturn) have been known since ancient times, since they are visible to the naked eye. Uranus' discovery expanded the boundaries of the solar system for the first time in modern human history. It was also the first planet discovered using technology (a telescope) rather than the naked eye.




Neptune is the eighth and farthest planet from the Sun in our solar system. IT is the fourth largest planet by diameter and the third largest by mass; Neptune is 17 times the mass of Earth and is slightly more massive than its near twin Uranus, which is 14 Earth masses, but slightly smaller due to its higher density. The planet is named after the Roman god of the sea. Neptune's atmosphere is primarily composed of hydrogen and helium, with traces of methane that account for the planet's blue appearance. Neptune also has the strongest winds of any planet in the solar system, measured as high as 2,100km/h. Discovered on September 23, 1846, Neptune is notable for being the first planet discovered based on mathematical prediction rather than regular observations.





Pluto, also designated 134340 Pluto, is the second-largest known dwarf planet in the solar system and the tenth largest observed body directly orbiting the Sun. Approximately one-fifth the mass of the Earth's Moon, Pluto is primarily composed of rock and ice. It has an eccentric orbit that is highly inclined with respect to the planets and takes it closer to the Sun than Neptune during a portion of its orbit.