THE SUN
The sun, eight planets, satellites, and some other celestial bodies known as asteroids and meteoroids form the solar system. We often call it a solar family, with the sun as its Head.
Figure 1.2: The Solar System
The sun is in the centre of the solar system. It is huge and made up of extremely hot gases. It provides the pulling force that binds the solar system. The sun is the ultimate source of heat and light for the solar system. But that tremendous heat is not felt so much by us because despite being our nearest star, it is far away from us. The sun is about 150 million km away from earth.
More to Know About Sun
1. ‘Sol’ in Roman mythology is the ‘Sun god’. ‘Solar’ means ‘related to the sun’. The family of the sun is, therefore, called the solar system. Write down as many words using the word solar on your own as you can.
2. Light travels at the speed of about 300,000 km per second. Yet, even with this speed, the light of the sun takes about eight minutes to reach the earth.
PLANETS
There are eight planets in our solar system. In order of their distance from the sun, they are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
An easy way to memorize the name of the planets in order of their distance from the sun is:
” My Very Efficient Mother Just Served Us Nuts.”
All the eight planets of the solar system move around the sun in fixed paths. These paths are elongated. They are called orbits. Mercury is nearest to the sun. It takes only about 88 days to complete one round along its orbit. Venus is considered as ‘Earth’s-twin’ because its size and shape are very much similar to that of the earth.
Till recently (August 2006), Pluto was also considered a planet. However, in a meeting of the International Astronomical Union, a decision was taken that Pluto-like other celestial objects (Ceres, 2003 UB313) discovered in the recent past may be called” dwarf planets.”
Figure 1.2: The Solar System
MERCURY - One orbit around the sun - 88 days, One spin on axis - 59 days.
VENUS - One orbit around the sun - 255 days. One spin on axis - 243 days
EARTH - One orbit around the sun - 365 days. One spin on axis - 1-day number of moons - 1
MARS - One orbit around the sun - 687 days. One spin on axis – 1 day, number of moons - 02
JUPITER - One orbit around the sun - 11 years, 11 months about 12 years. One spin on axis – 9 hours, 56 minutes, number of moons - about 53
SATURN - One orbit around the sun - 29 years, 5 months. One spin on axis - 10 hours 40 minutes, number of moons – about 53
URANUS - One orbit around the sun - 84 years. One spin around an axis – 17 hours 14 minutes, number of moons - about 27
NEPTUNE - One orbit around the sun - 164 years. One spin on axis-16 hours 7 minutes, number of moons - 13.
The Earth
The earth is the third nearest planet to the sun. In size, it is the fifth-largest planet. It is slightly flattened at the poles. That is why its shape is described as a Geoid. Geoid means an earth-like shape.
Conditions favourable to support life are probably found only on the earth. The earth is neither too hot nor too cold. It has water and air, which are very essential for our survival. The air has life-supporting gases like oxygen. Because of these reasons, the earth is a unique planet in the solar system.
From outer space, the earth appears blue because its two-thirds surface is covered by water. It is, therefore, called a blue planet.
Word Origin
Many words used in a language may have been taken from some other language. Geography, for example, is an English word. It has its origin in Greek, which relates to the description of the earth. It is made of two Greek words, ‘ge’ meaning’ ‘earth’ and ‘graphia’ meaning ‘writing’. Find out more about the earth.
THE MOON
A Satellite
A Satellite is a celestial body that moves around the planets in the same way as the planets move around the sun.
Our earth has only one satellite, that is, the moon. Its diameter is only one-quarter that of the earth. It appears so big because it is nearer to our planet than other celestial bodies. It is about 3,84,400 km away from us. Now you can compare the distance of the earth from the sun and that from the moon.
The moon moves around the earth in about 27 days. It takes exactly the same time to complete one spin. As a result, only one side of the moon is visible to us on the earth. The moon does not have conditions favourable for life. It has mountains, plains, and depressions on its surface. These cast shadows on the moon’s surface. Look at the full moon and observe these shadows.
Figure 1.3: The moon as seen from the space
More to know About Moon
Neil Armstrong was the first man to step on the surface of the moon on 20 July 1969.
A Human-made Satellite
A Human-made Satellite is an artificial body. It is designed by scientists to gather information about the universe or for communication. It is carried by rocket and placed in the orbit around the earth.
Figure 1.4: Human-made Satellite
Some of the Indian satellites in space are INSAT, IRS, EDUSAT, etc.
ASTEROIDS & METEOROIDS
Asteroids
Apart from the stars, planets, and satellites, there are numerous tiny bodies which also move around the sun. These bodies are called asteroids. They are found between the orbits of Mars and Jupiter (Figure 1.2). Scientists are of the view that asteroids are parts of a planet which exploded many years back.
Figure 1.5: Asteroid
Meteoroids
The small pieces of rocks which move around the sun are called meteoroids. Sometimes these meteoroids come near the earth and tend to drop upon it. During this process due to friction with the air, they get heated up and burn. It causes a flash of light. Sometimes, a meteor without being completely burnt falls on the earth and creates a hollow
GALAXY & UNIVERSE
Galaxy
Do you see whitish broadband, like a white glowing path across the sky on a clear starry night? It is a cluster of millions of stars. This band is the Milky Way galaxy (Figure 1.6). Our solar system is a part of this galaxy. In ancient India, it was imagined to be a river of light flowing in the sky. Thus, it was named Akash Ganga. A galaxy is a huge system of billions of stars, and clouds of dust and gases
Figure 1.6: Milky Way
Universe
There are millions of such galaxies that make the Universe. It is difficult to imagine how big the universe is. Scientists are still trying to find out more and more about it. We are not certain about its size but we know that all of us – you and I belong to this universe.
Can you relate yourself to the universe now? You are on the earth and the earth is a part of the solar system. Our solar system is a part of the Milky Way galaxy which is part of the universe. Think about the universe and the fact that it contains millions of such galaxies. How do you fit in the picture?