1. THE EARTH AND ITS NEIGHBOURS For Class -iv

2. THESKY

The Sky its full of heavenly objects. Some of them are brighter than others. The tiny specks of light that appear in the sky are called star. The slow-moving bright bodies are called planets.

3. STARS

A Star is a huge ball of gases. It gives out light and heat. The sun is a star. It is star sun. Some are a thousand times the bigger than it. Stars shine for millions of year. Patterns of star are called constellations. The stars in the night sky are only a part of a huge star cloud,

known as milky way galaxy. Milky way is a spiral-shaped galaxy.

nearest to the earth. Some stars are smaller than the 4. PLANETS

Earth is a planet. It does not have light or heat of its own.The eight planets are Mercury, Venus,Earth,

Mars,Jupiter,Saturn,Uranus and Neptune. Pluto was

the ninth planet.However, pluto is no longer considered a planet. It was called a dwarf planet in 2006 and then a plutoid in june2008. The planets were named after the gods and goddesses of Greece and Rome. Mars for example is the name of a Roman God of war. Mars look different than others as it is reddish in colour. Mercury and Venus are seen in the morning and evening. Venus is called the morning or the evening star. Jupiter is brighter and the largest of all the planets. Saturn is not so bright. It has a system of rings around it. The Planets which are further away can be seen with the help of a telescope.

5. SATELLITES

Satellites are small heavenly bodies which revolve around the planets Some planets have their own satellites. The moon is a natural satellite of the earth.

6. SOLAR SYSTEM

The sun and the eight planets revolving around it along with their satellite make up the solar system.

7. OUR PLANET EARTH

THE earth is a very beautiful planet. It has land and water,mountains and valleys, hills and plains. It has plants and flowers,animals and people. It was born as a huge ball ofdust and hot gases. The ball kept on spinning. As it spun, its outer surface grew cold and hard. Some gases escaped while some were trapped inside. Today the earth is like a half-boiled egg! Its outer surface is hard ,but, deep inside, it has hot, molten material. The outer surface is called the crust. The inside portion is called the core. Between the outer crust and the inner core, there are layers of rocks/ minerals and metals in solid form. This layer is called the mantle. Today, even an extremely high temperature and is under great pressure. The boiling liquids and gasesof the core push against the outer crust. The weak spots of the earth crack open under this pressure, letting the hot boiling liquids and gases gush out. This is how a volcano is formed. An active volcano is one which erupts regularly.A dormant volcano is one which has not erupted for a long time. A volcano is said to be extinct if it has not erupted recorded history.

8. MOVEMENTS OF THE EARTH

The earth moves on its axis. The axis of the earth is an imaginary line that runs through the centre of the earth. This axis slightly tilted. The two points where the axis seems to enter are called the poles: the North pole and the South pole. The equator is another imaginary line around the earth, exactly halfway between the poles. It divides the earth into two equal halves, the Northern Hemisphere and the Southern Hemisphere. The movement of the earth on its axis is called Rotation. Besides rotating on its axis, the earth also revolves around sun. This movement of the earth around the sun is called Revolution. The earth moves continuously. It revolves around the sun in a fixed path called an Orbit. One revolution completed in 3651/4 days. This time period is called a solar year.

9. SEASONS OF THE EARTH

As the earth orbits around the sun, the longer days of summer change into the shorter days of winter. This means that the length and temperature of the days change. This causes the seasons: Spring, Summer, Autumn and winter. The axis of the earth is tilted at an angle. This is why when the Northern Hemisphere is away from the sun, The Southern Hemisphere is towards it. Again the southern hemisphere is away from the sun when the Northern Hemisphere is towards it. So, the season in the Northern Hemisphere can never be the same as the season in the Southern Hemisphere.

10. HOW ARE SEASONS FORMED?

What happens when the earth goes around sun?

When the north pole is towards the sun. it is summer in the Northern Hemisphere. The days seems to hotter because the suns rays fall directly. At the North pole there is sunlight for most of the day and some part of the evening. During this time the south pole is turned away from the sun. So, the sun's rays do not reach the south pole and there is not much daylight. It is winter in the Southern Hemisphere.

When the North Pole is turned away from the Sun, it is winter in the Northern Hemisphere. The days are shorter and the sun seems low in the sky. Now it is summer in the Southern Hemisphere.

11. FESTIVALS AND HEAVENLY BODIES

• You must have seen in your school diary and calendars that the holiday for Id is marked with Depending on the appearance of the moon. This is because the Islamic calendar is based on the phases of the moon. Many other Indian festivals too are linked to the movement of the moon, the planets, the sun and the seasons. Holi marks the coming of spring. Baisakhi, Onam, Pongal Bihu and lohri are linked to the seasons. The days of the week in the Indian calendar are named after the planets. For example, shanivaar means the day of shani or Saturn.

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