4th Class Science Our Universe Stars and Planets

Stars and Planets

Category : 4th Class

*       Introduction


Our Universe: Universe is the collection of all the objects in space and the space itself. The universe includes everything that our eye can see and even those things which we can't see. When we look at the sky on a dark clear night, we see the entire sky dotted with countless stars, some bright and some are not so sight. On observing these dotted stars, we find that many of them twinkle and some do not twinkle. These objects, which do not twinkle are the planets. The stars, the planets, the moon and everything that we see in the sky are called heavenly bodies.

    Heavenly Bodies in the universe


The vast expanse of space that contains all the matters from the smallest particle to the planets, sun, moon, stars, asteroids and the biggest galaxy is called the universe. We do not exactly know how big our universe is. It is believed to be growing outward in every direction. Nobody really knows how the universe was formed. Most scientists believe that at first everything was solid heavy ball of matter. This ball exploded billions of years ago - and our universe was born. The explosion is called the big bang. How our universe was formed is still only a theory (an idea), astronomers continue to investigate the theory.


*        Stars and Planets


*         Stars

The heavenly bodies which appear to twinkle in the sky are called the stars. A star is a huge ball of hot burning gases. It gives out heat, light and energy. The stars that appear as twinkling points of light in the night sky are very far away from us. Hence they appear to be very small. The greatest characteristic of star is that they have light of their own. Sun is the nearest star to us. Hence the sun appears to be so big and glowing. Without the sun's heat and light our earth would have been very cold. Life on earth would have not been possible. Sun is the ultimate source of energy for us.

In a dark night sky we can see millions and millions of stars. To make it easy to identify stars, some have been grouped together to from shapes. These groups of stars are called Constellation. The shape of the constellation resemble familiar objects. To easily identify constellation, we should know what a particular constellation looks like and where to look for it in the night sky. Let us know about some constellations.


*       Ursa Major

It is one of the most famous constellations, which can be seen during summer time in the early part of the night. It is also known as big dipper or great bear.

         Ursa Major  


*         Orion

Orion is another constellation that can be seen during winter in the late evenings. It is most magnificent constellation. Orion is also known as the hunter.


A constellation need not have only five to ten stars. It can have large number of stars. We can see only the bright stars in a constellation with our naked eye.  


*           Planets

The heavenly bodies that do not have any light of their own and move around the stars are called planets. Planets reflect the light that fall on them from the star. Planets keep changing their positions with respect to the stars, as they move around a star in a certain orbit. Orbit is that definite path in which a planet moves around the star. In our solar system sun is situated at the centre and eight planets move around it in their orbits. Each planet rotates on its axis as well. The eight planets in the increasing order of distance from the sun are as follows. Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

                 Our solar system  


*         Mercury

It is the closest planet to the sun. It is very hot during the day and very cold at night. It is also the smallest planet in our solar system. Mercury can be observed just before sunrise or just after sun set. Mercury rotates from west to east. It is made up of rocks and metals. Life does not exist as there is no air and the temperature is extreme. Mercury takes 88 days to go around the sun.



*           Venus

Venus is the second planet from the sun. It is the brightest planet in the night sky. It shines brightly some times in the western sky as the "evening star" and at other time in the eastern sky, before the sun rise, as the "morning star". Venus is made up of rocks and metals. Rotation of venus on its axis is different from most of the planets. It rotates from east to west.



*         Earth

Earth is the third planet in our solar system. Earth appears bluish green from the space due to the presence of water and land mass. It is the only planet in our solar system to have life in it. The special condition that support life on earth is its right distance from the sun, as a result it has the right temperature range. Presence of water and suitable atmosphere are other conditions. Rotation of earth on its axis is from west to east. It takes 24 hours to rotate on its axis and 365 days to complete one revolution around the sun.



*         Mars

It is the fourth planet from the sun. It appears reddish in colour due to its red soil and rocks. It is also called as red planet. It is made up of rocks and metals. Like most planets it also moves from west to east. It takes 24 hours and 37 minutes to move on its axis. Mars is about half the size of the earth.



*           Jupiter

Jupiter is the largest planet of the solar system. It is a giant ball of gases and is extremely hot. Jupiter has a big great red spot. This spot is actually a huge storm, which has been blowing on its surface for at least a few hundred years. Like most planets it moves from west to east. Jupiter spins very fast, pulling its clouds in to stripes. This is why Jupiter shows striped pattern when we carefully look at it with telescope.



*         Saturn

Saturn is the most beautiful planet of our solar system. Its spectacular rings distinguish it from all other planets. It is also a gas planet. The spectacular rings of the planet cannot be seen with the naked eye, we can observe them with a small telescope. It has seven shining rings around it. Another most amazing fact about the planet is that it is the least dense of all the planets in our solar system (the planet is very light).




*         Urnanus

Urnanus is the seventh planet from the sun and is among the outermost planet. It is a large gas planet as it is far away from the sun. Uranus takes 84 years to go around the sun. Like venus it also rotates form east to west. Most striking feature of uranus is that it has highly tilted rotational axis. This result in its orbital motion, which appears to roll on its side. The planet takes only 17 hours to spin on its axis.



*         Neptune

Neptune is the farthest most planet of our solar system. It is made up of mostly gases. When observed though a telescope two spots can be seen on its surface. These spots are actually big storms with very fast blowing winds. The day is shorter on Neptune as it takes only 16 hours and 7 minutes to rotate around its axis. Neptune, being the outer most planet, takes the longest time to go around the sun.






       After our own sun, the nearest star to the earth is

(a) Sirius

(b) Moon

(c) Pole star

(d) Alpha centaury                         

(e) None of the above


Answer: (d)


Alpha centaury is 4.3 light year the earth.



      Name a planet which can float in water

(a) Earth

(b) Neptune

(c) Venus

(d) Saturn                                           

(e) Mars                 


Answer: (d)

Saturn is the least dense of all our planets (is very light). Its density is less than water and so it can float in water.

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