INTRODUCTION TO THE UNIVERSE FOR KIDS
Definition of the Universe for kids-
The universe is a wide-open space that holds everything we see in the sky, including our home, the Earth.
At least once in our life, every one of us has looked into the night sky and wondered what it might hold in it. Is it just the Moon and twinkling stars or something more bizarre than our expectations? Away from our daily life here on Earth, the Universe is a weird and truly wonderful place. Stars are born and explode. Star clusters, called galaxies, fly away from each other. The straight path of light is really bent, and time goes faster or slower. Modern science explains some of these mind-boggling events – but not all. More we learn about it the stranger it gets.
WHAT IS THE SIZE OF THE UNIVERSE?
No-one really knows how big the Universe is. It may have an end, which is too far away to detect or it may have no end at all. It may even curve around on itself, so it is endless like a circle. But we do know that it is the biggest thing we know and includes all the empty parts of space between the stars. Most scientists think that the Universe began with the gigantic explosion – the Big Bang, which happened billions of years ago. Since then it has been growing bigger and bigger in all directions, creating more and more space.
EXPLORATION OF THE SPACE AND THE UNIVERSE
In ancient times, people believed that the Earth was flat and the center of everything. Gradually, they learned that it was not flat, but ball-shaped and is just one of the eight planets that travel around our star, the Sun. And the Sun is really just an ordinary star, like many millions of others in the Universe. Early astronomers simply used naked eyes to explore the night sky. However, modern astronomers looked through big, powerful telescopes and found other celestial objects. All the objects that we see in the sky, including the stars, planets, galaxies, meteors, comets, etc. are called celestial objects.
There are countless billions of stars in the Universe. Each star is a huge fiery ball of gas, mostly hydrogen like our Sun. Yes, our Sun is also a star and it is 109 times bigger than the Earth. All stars other than the Sun appear as the tiny dot in the sky because they are very far away from us. To know more about Stars click here.
The Sun is a star. It is located at the center of our solar system. It is about 150 million kilometers away from Earth. Being nearer to the Earth than any other star, it looks big and bright, like a ball of fire. It is the largest and the heaviest member of the solar system. It is about 109 times bigger than the Earth with a diameter of about 13,92,000 kilometers. Its mass is about 3,33,000 times that of the Earth. The temperature of the outer surface of the Sun is nearly 6000oC, which is enough to melt almost any substance. To know more about the Sun click here.
THE SOLAR SYSTEM
The word ‘solar’ derives from the Latin word ‘sol’ meaning the Sun. The solar system is the family of the Sun. It consists of the Sun at the center, the eight planets, their satellites (moons), the asteroids, meteors, and comets. All the members of the solar system move around the sun in different paths, known as orbits. This system is the Earth’s local neighborhood in space. The Sun holds everything together by an invisible force called gravity. To know more about the solar system, click here.
The word ‘planet‘ is derived from the Greek word ‘wanderer‘ as they revolve around the Sun. There are eight planets in our solar system. They move around the Sun in elliptical orbits. In order of their distance from the Sun, they are – Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. The first four planets i.e. Mercury, Venus, Earth, and Mars are quite close to Earth and often known as inner planets. The last four planets i.e. Jupiter, Saturn, Uranus, and Neptune are far away from the sun and often known as outer planets. Another reason for their division as inner and outer planets is the presence of an asteroid belt between Mars and Jupiter. As planets comprise of solid material and gases, thus they do not have their own heat and light. They shine with the light reflected from the Sun. For quick facts about the planets, click here.
Satellites are small bodies that revolve around the planets. They are of two types; natural and artificial. The moon is a satellite of the Earth and it is a natural satellite. An artificial satellite is a man-made object that orbits the earth or other planets. Like planets, satellites also do not have any heat or light of their own. They shine by reflecting the light from the Sun. The Earth is not the only planets which have natural satellite or the Moon. Mars has two, Jupiter has 63, Saturn has 34, Uranus has 27 and Neptune has 13 natural satellites. Ganymede is the largest natural satellite of Jupiter while Titan is the largest satellite of Saturn. To know more about satellites, click here.
The Moon is the Earth’s only natural satellite. It is about 3,85,000 kilometers away from Earth. Its diameter is about one-fourth of the Earth. The Moon is cold and dry, with a rocky surface. There is no air and water on the Moon. In the absence of atmosphere, the Moon has no protection against the strong rays of the Sun. This leads to extreme changes in temperature during the day (123oC) and night (- 233oC). All these features make it impossible for life to exists on the Moon. The Moon gravity is one-sixth of the Earth. So, you would be able to lift even heavy objects very easily on the moon. If you can jump one meter on the Earth, you will be able to jump six meters on the Moon. To know more about the Moon click here.
Along with the planets and their moons, thousands of smaller bits of rock and ice circle around the Sun. They range from tiny particles to mini planets hundreds of miles across. These are asteroids or planetoids. They are leftover debris of the solar system – fragments too scattered to gather together to form a proper planet. They revolve around the sun in their own orbits. Most of these rocks lie in a wide band between the orbits of Mars and Jupiter, called the asteroid belt. There are about 40,000 such asteroids, the largest of which is Ceres. To know more about asteroids click here.
METEOROIDS, METEORS, AND METEORITES
Meteoroids are those rocks which somehow spin out of the asteroid belt and starts revolving around the Sun in different orbits. Some of these meteoroids enter the Earth’s atmosphere with great speed and due to friction, get heated up and start glowing. We call these glowing and moving objects, meteors or shooting stars. Fortunately, most meteors are so small they burn as they hit the atmosphere and never reach the Earth’s surface. But, some are quite large and survive the fall and land on the Earth’s surface. They are then called meteorites. To know more about meteoroids click here.
Comets are celestial bodies made of snow, dust particles, and frozen gases. They revolve around the Sun in elongated orbits. Due to their elongated orbit, they come near to the Sun after a very long period. Normally, comets have an appearance of a dirty snowball, but when they approach the Sun, the gases get heated up and start glowing. Dust, vapors, and gases are blown out in a form of huge tail millions of miles long. Because the tail is blown by the Sun, it always faces away from the Sun. As the comet passes the Sun and heads out into deep space again, its tail faces the direction it is moving. To know more about comets click here.
Billions of stars together make a galaxy. As our Sun is the star, thus it is also a part of a galaxy. We call it, the Milky Way. Our Galaxy is not the only one in the Universe. In fact, it is just one of the countless millions of galaxies out there. Galaxies are not spread evenly through the Universe. They are clumped together in clusters of anything from half a dozen to several thousand. Our Galaxy is part of a neighborhood cluster of 3,000 galaxies, the local group.
There are several different shapes of galaxies – spiral, elliptical, barred spiral, irregular, etc. Our galaxy is of the spiral shape. It is a vast collection of 100 billion stars, about 1,06,000 light-years across. From the Earth, it appears pale streak of light stretching across the night sky. It almost seems like someone has spilled milk across the sky, which is why it is called the Milky Way. To know more about galaxies, click here.
A nebula or nebulae, named from the Greek word ‘cloud‘ are a vast interstellar cloud of dust, hydrogen, and other gases. Like clouds in the sky, nebulas comes in interesting shapes like a flower, and fingers, etc. The nebula is a region where stars are born. In this huge area of hydrogen gas, gravity pulls gas and dust together to form clumps. As each clump pulls itself tighter it begins to get hot. If the clump reaches the temperature of 10 million degrees Celsius, nuclear fusion begins and clumps changes to glowing star. Whatever is left, form planets which revolve around the Star. The most famous nebula in the space is the Orion nebula. The Orion nebula is the most active area of star formation in our galaxy. To know more about nebula click here.
Supernova is a giant explosion generated by a dying star. For a few weeks, it shines with a brightness of millions of Suns. In a medium-sized star, the heat tries to make the star bigger, but gravity balance this expansion and tries to shrink it. So the star stays the same size and glows steadily. At the core of the star, hydrogen fuses to form helium. When hydrogen exhausts, the core shrinks and begins fusing helium to form other heavy elements. The outer layer of gas cool and swell, and it becomes a red giant. In the biggest stars, more changes take place in the core, and the star suddenly takes in energy instead of giving it out. It collapses in seconds. The collapse of a huge star is like a giant nuclear explosion called a supernova. To know more about supernova click here.
All stars do not die in a magnificent explosion, a supernova. A small star when runs out of hydrogen, gradually cool and shrinks into a white dwarf and die somewhat silently. As a rule of thumb, stars with mass less than 8 times of our Sun, will form white dwarfs. Such stars when gets old, hydrogen in their core is exhausted and the star begins to fuse helium to form heavier elements. While doing so, it starts shedding its outer layer. When this process is over, what remains is its core and a white dwarf is born. A mass of the white dwarf is around 1.45 times that of the former star. To know more about white dwarfs click here.
When a star dies in a supernova, it forms a neutron star. As a rule of thumb, after a supernova, a star with a mass between 8 to 20 times that of our Sun, will end up as a neutron star. The supernova blows off all the star’s layers, except the iron core. The gravity of iron core shrinks it further to such an extent that protons and electrons fuse together and we are left with only neutrons. At this time the core of the star is about 20 kilometers wide and we call it a neutron star. Even with this size, the neutron star has a mass of 1.5 to 5 times the mass of our Sun. To know more about neutron stars click here.
A pulsar is a highly magnetized, rotating neutron star. It sends out powerful electromagnetic and radio signals as regular pulses, like a flashing beacon. Pulsars in the Universe can be more easily correlated with a lighthouse on the Earth. They are few kilometers across and spin insanely fast. The fastest known pulsar is rotating with a record speed of 1100 rotations per seconds. To know more about pulsars click here.
Magnetars are a type of neutron star, like pulsars, but with an extremely powerful magnetic field. They are one of the densest objects in the Universe. They convert heat and rotational energy into a very strong magnetic field. The magnetic field made by magnetar is quadrillion times more than that of the Earth. During a supernova, the spin, the temperature, and the magnetic field of the neutron star determine that it will be a pulsar or magnetar. As per estimate about one in ten supernova explosion results in a monetary rather than a more standard neutron star or pulsar. To know more about magnetars click here.
Black holes are the weirdest objects in the Universe. Till date, a black hole is just a theory and we hardly know anything about it. But, whatever we know makes it more and more strange. Black holes are the objects in the Universe where the gravity is so strong that it sucks in everything – including light. As even light could not escape a black hole that’s why they appear black. So how do we know black holes exist? We can identify a black hole by observing the light and the object around it. Black holes are formed when a star of mass more than 20 times that of our sun dies in a supernova. They are the heaviest objects in the Universe. To understand the density of a black hole, imagine a grain of rice with the mass that of the Earth. To know more about the black holes click here.