Beyond Earth

Class 06 Science

At night, when you look up at the sky, you see many stars. Some stars are bright and others are dim. Stars shine with their own light.

Stars and Constellations

Some groups of stars appear to form patterns which are like shapes of familiar things. Recognising stars and their patterns was a useful skill for navigation in the olden times. Before the arrival of modern technology or even before the invention of the magnetic compass, it helped people, particularly sailors and travellers, in finding directions at sea or on land. It is still used in emergencies as a backup method.

The regions of sky, which include the groups of stars, are defined as constellations.

The constellation Orion is often represented as a hunter. There are three stars in the middle, which represent the belt of the hunter. Some people imagine that the hunter Orion, followed by his dog (constellation Canis Major), is battling a bull (constellation Taurus). Canis Major contains a star called Sirius, which is the brightest star in the night sky.

The Pole Star appears stationary in the North direction, which helps to locate the North direction in the Northern hemisphere.

Solar System

The Sun, eight planets, their moons, and many smaller objects including asteroids, and comets, together form the Solar System.

The Sun

The Sun is a star. It is the star closest to us. It is an extremely hot spherical ball of gases. The Sun gives out a huge amount of energy, and that is why it glows so brightly. The Sun produces heat and light, and is the main source of energy on the Earth.

There are many more objects in the sky. The Earth, along with some of these objects, and the Sun together form the Solar System. Most of these objects move around the Sun. The movement of an object around the Sun is called revolution.

Planets

A planet is a large, nearly spherical object that revolves around the Sun. Our Earth is a planet as it revolves around the Sun. The Earth takes nearly one year to complete one revolution. Like the Earth, there are other planets that revolve around the Sun.

The eight planets, in order of their increasing distance from the Sun, are

1. Mercury
2. Venus
3. Earth
4. Mars
5. Jupiter
6. Saturn
7. Uranus
8. Neptune

The inner four planets nearest to the Sun - Mercury, Venus, Earth and Mars - are smaller in size. They have solid surfaces with rocks on them.

Venus is usually seen shining brightly at dawn and dusk, and is commonly called the Morning Star or the Evening Star, even though it is not a star. Mars is called the Red Planet because it appears red. This is because the soil on Mars is reddish in colour.

A large portion of the Earth’s surface is covered with water and thus, it appears blue from the space. Due to this, the Earth is also called the Blue Planet.

The four outermost planets - Jupiter, Saturn, Uranus and Neptune - are much larger compared to the Earth, and are mostly made of gases. These giant gaseous planets have large flat ring-like structures around them which are made of dust particles and rocky material.

Planets get most of their energy from the Sun. So, the farther they are, the colder they are in general. The presence of an atmosphere on a planet can trap heat which can significantly change the temperature of a planet. That is why Venus, for example, is hotter than Mercury, although it is farther from the Sun.

Natural Satellites

Objects that move around planets are commonly called satellites. They are smaller in size than planets. Moons are natural satellites of planets. The Earth has one Moon, while Mars has two moons. Jupiter, Saturn, Uranus and Neptune have a large number of moons.

The Moon

Earth’s natural satellite, the Moon, takes about 27 days to complete one revolution around the Earth. It is our nearest neighbour in the space. Unlike on the Earth, there is hardly any atmosphere on the Moon.

The Moon is about a quarter the size of the Earth in diameter. The Moon’s surface shows circular bowl-like structures called craters. Most of these craters have been formed due to the impact of asteroids or rocks from the space hitting the Moon’s surface. Since there is no atmosphere, water or life on the Moon, these features stay on the Moon’s surface for a very long time.

Asteroids

The Sun and the planets are nearly spherical in shape. There are many small objects in the Solar System which are rocky and irregular in shape. These are called asteroids. Many of these asteroids revolve around the Sun in paths that lie between those of Mars and Jupiter. This region is called the asteroid belt. Occasionally, asteroids pass very close to the Earth.

Comets

Sometimes we have visitors from the outer regions of the Solar System. These objects with long tails are called comets. They are made up of dust, gases, rocks and ice. As a comet approaches close to the Sun, the frozen material in it starts evaporating. This evaporating material forms the tail of the comet. Comets appear dim as they move away from the Sun and then, it is not possible to see them with the naked eye.

Many comets have been found that revolve around the Sun. These comets approach close to the Sun periodically. However, there are a few comets that escape and move out of the Solar System. Few other comets get broken up, or fall into the Sun or other planets when they approach them.

The Milky Way Galaxy

A galaxy has millions to billions of stars. The Solar System is part of the Milky Way Galaxy or Ākāśha Gangā.

The Universe

There are many galaxies in the outer space beyond the Milky Way Galaxy. Scientists study them to understand the stars, galaxies and the universe.