Universe is everything around us. It is the Sun, stars, planets, galaxies, dust and clouds. It includes all kinds of physical matter, energy and time. It is everything that can be touched, felt, sensed and detected. The universe is incredibly vast. It has millions of galaxies which have billions of stars.
These galaxies are far away from each other by millions of light years. A light year is unit to measure astronomical distances. It is the distance travelled by light in vacuum in one year. (1 light year is approximately equal to 1013km). The size of the universe is already vast and it is expanding. It is becoming larger and larger.
But our universe was not always like this. According to scientists, the universe is created by Big Bang which happened about 14 billion years ago and from then the universe is growing.
Our solar system is in the Milky Way galaxy. The galaxy contains 200 billion stars in addition to the Sun.
Our solar system comprises of the Sun and all the objects that revolve around it. The Sun is the center of the solar system. All the objects revolving around the Sun revolve in paths which are called orbits. Other than the Sun the major part of the solar system is determined by the planets that revolve around the Sun. There are eight planets in the solar system which are as follows in the order of the increasing order of the distance from the earth:
Mercury is the closest planet to the Sun. It is also the smallest planet. The days are very hot in it, while the nights are extremely cold. It has no natural satellite and no life is possible on this planet.
Venus is the second planet from the Sun. Its size is approximately same as that of the earth. It is the third smallest planet. It has no natural satellites. The planet is the hottest of all the planets because its atmosphere has high concentrations of carbon dioxide gas which traps the heat. It shines brightly among all the stars so, it is also known as the morning and evening star.
Earth is third planet from the Sun. It is fourth smallest in terms of the size. It has one natural satellite, Moon. Moon revolves around the earth, and the earth revolves around the Sun rotating on its own axis.
It is the only planet where life is known to exist. It is the only planet which has 21% of oxygen in its atmosphere. It is the only one that has water in its atmosphere. It takes 364 1/4 days to revolve around the Sun and 24 hours to revolve on its own axis.
The Moon is the only natural satellite of the earth. It can be seen from Earth. It is about 380,000 km away from the Earth. It is about quarter the size of the earth. The gravity on the moon is one-sixth of the Earth’s gravity. It means that something will be six times lighter on the Moon than on Earth.
The surface of the moon is covered with rocks and dust. It has mountains and flat plains. There are also large round ditches which are called craters on the surface of the moon. No life can exist there since it has no air and water.
Mars is the fourth planet from the Sun. It is also known as the red planet. The red color of the planet is due to the presence of the iron oxide in the soil of the planet. It has two natural satellites. It is the second smallest planet in the solar system. Nowadays research is being done to find if life can sustain there.
It is the largest planet of the solar system. It is fifth from the Sun. It is about 2.5 times the mass of all the other planets put together. It is a giant ball of gas, with no solid surface. It has 67 known natural satellites. The atmosphere on this planet is very cold.
Saturn is known for its distinct ring around it. These rings are made up of ice and dust. It is the second largest planet. It is sixth from the Sun. It has many similarities with Jupiter with respect to its atmosphere. It has no solid surface. It is made up of gases. It appears yellowish in color. It has 62 confirmed natural satellites
Uranus is the third largest planet in the solar system. It is seventh from the Sun. It is very cold and gaseous planet. It has greenish color. It has 27 known moons.
Neptune is the farthest from the Sun. It is the fourth largest planet of the solar system. It has 14 known satellites. It is the coldest planet. It has 17 times the mass of the earth. It is the densest planet.
Sun is a star which is the center of the solar system. It is yellow in color. The size of Sun is about 100 times that of the earth. It has a mass of 1.9891×1030 kg, which is 333,000 times the mass of the Earth. It is so big that a million of earth can fit in it.
It gives heat and light. It also gives out ultraviolet rays which are very harmful; they can cause sunburns and may cause cancer. The distance between Sun and earth is about 150,000,000 km. It takes about 8 minutes to reach light from Sun to the earth.
A comet is nothing but a ball of mostly ice that moves around the Sun. They are often described as dirty snowballs. They are very far away from the Sun but some of them come near the earth. They are often seen to have a tail.
The tail of the comet is nothing but the ice of the comet melted by the Sun. The tail does not trail behind, but it actually points directly away from the Sun, because it is blown by the solar wind. The only solid part of any comet is in the middle or nucleus.
Like planets they also revolve around the Sun in orbits. They are made up of rocks or metals. They are much smaller than the planets. They also don’t have light of their own like the other planets. From the earth they appear like stars. They are also called as planetoids or minor planets because they have many resemblances with planets. There are billions of asteroids are present in the universe. A belt of asteroids lie between the orbits of Mars and Jupiter which is called as the asteroid belt.
Meteors are commonly known as shooting star or falling star. This falling star is actually rock falling from the space on the surface of the earth.
When a meteor enters the earth surface it is burnt up. The trail they leave is less than 1 second. If it does not burn completely and hits the surface of the earth it is called as meteorite. It leaves a hole in the ground which is called a crater. When meteors many meteors fall together then it is called as the meteor shower.