The solar system

What is the solar system? • The solar system is made up of the Sun, the 9 planets the planets are sun, mercury,

Venus, earth, mars, Jupiter, Saturn, Uranus, and Neptune. And 5 dwarf planets and their 174 known moons, asteroids, comets, dust and gas. The planets, asteroids, and comets travel around the Sun, the centre of our solar system.

• Most of the bodies in the solar system travel around the Sun along nearly circular paths or orbits, and all the planets travel about the Sun in the anticlockwise direction.

• Solar system formation began billions of years ago, when gases and dust began to come together to form the Sun, planets, and other bodies of the solar system.

How the universe and the solar system were formed?

At least since the earliest recorded writings, people – scientists, astronomers, philosophers, and almost everyone else – have been searching for the answer to how the universe was formed. There is no single model for how the universe was formed, but scientists have agreed on a most popular model.

The most popular theory is called the nebular hypothesis. It did fall out of favour for a number of years, but now it is back as the definitive model. According to the nebular hypothesis, our Solar System began around 4.6 billion years ago when part of a molecular cloud of interstellar gas, which was filled with particles of ice, dust, rock, and other particles, collapsed. These clouds collapsed from some kind of turbulence that caused it to heat up and eventually turn into a star.

Asteroids

• Asteroids are rocks. They are rocky objects with round or irregular shapes up to several hundred km across, but most are much smaller is about 1km in diameter. That obits the sun.

More than 100,000 asteroids lie in a belt between Mars and Jupiter. These asteroids lie in a location in the solar system where there seems to be a jump in the spacing between the planets. Scientists think that this debris may be the remains of an early planet, which broke up early in the solar system.

The chances of an asteroid colliding with Earth are very small! But some do come close to Earth.

Asteroids

Comets are icy objects that release gas and dust as they orbit the Sun.

The solid part of a comet is called the nucleus and is mainly made of frozen water, dust and sometimes other frozen substances such as ammonia.

Solar radiation heats the nucleus and gives it an atmosphere of gas and dust called the coma.

A comet's distinctive tail is caused by solar radiation and a stream of charged particles that constantly jets away from the Sun called the solar wind.

It is thought that comets are material leftover from the formation of the outer planets.

Comets

• Supernovas are exploding stars. Red giant stars explode when they have used up their hydrogen and helium fuel, and converted most of their atoms to iron atoms.

• Red giant stars have a lot of gravity pulling them inward. Normally they don't collapse inward because the nuclear fusion going on inside them pushes energy outward and balances the pull of gravity. When the nuclear fusion stops, the force of gravity pulls the star inward. When the inner shell hits the iron core, it makes a huge shock wave and the star explodes. When a star explodes, it shoots out billions of atoms into space, where they form a huge cloud of dust called a nebula. Other than hydrogen and helium, pretty much all of the atoms that are around today were originally made inside stars and then shot out into space when their star became a supernova.

Supernovas

• Black Holes are theoretical objects. A black hole is an object which has such high gravitational pull that not even light can escape. That happens when the speed you would have to be going to overcome the gravity and get away from the black hole is bigger than the speed of light.

• There may also be a lot of teeny-tiny black holes, called micro black holes, but nobody has seen one or proved that they must exist. These micro black holes might have formed during the Big Bang.

• Many astronomers think that there are black holes at the centre of galaxies of stars, including our galaxy, the Milky Way. These would be extra-big black holes, millions or billions of times the mass of our Sun. Nobody's ever seen a black hole.

Black holes

• Meteors or meteorites are bits of rock and ice - usually a mixture of rock and iron and nickel but sometimes just rock or just iron - from out in space that get sucked into the gravity of the Earth and fall through our atmosphere to the ground.

• Most meteors are tiny, the size of pebbles, and most of them fall into the ocean, because more of the Earth is ocean than there is land. Even if they fall on land, these tiny meteors don't do any harm. Sometimes, though, much larger meteors do fall to Earth.

Meteors

• A galaxy is a group of millions of stars that are relatively near each other. Most stars seem to be in one or another galaxy. Earth's own star, the Sun, is in the Milky Way galaxy. Small galaxies have about ten million stars, while big galaxies sometimes have a trillion stars in them. There are probably more than a hundred billion galaxies in the Universe.

• Gravity holds the stars together into a galaxy, just as gravity holds planets in orbit around a star. In most galaxies, the stars also orbit around the centre of the galaxy the way planets orbit around a star but the peoples don’t know what is in the middle of galaxies. Some astronomers think there might be giant black holes in the middle of galaxies.

Galaxies

Evidence shows that the universe is changing?

• Edwin Hubble was a very famous astronomer who was interested in the structure of galaxies and the Universe. He set about investigating distant galaxies and made an amazing discovery. He found that the spectra of light from these galaxies had been shifted towards the red end of the visible spectrum. This meant that the light had been red-shifted. dynamic

How the universe was formed?• Most astronomers believe the Universe began in a Big Bang about 14 billion years ago. At that time,

the entire Universe was inside a bubble that was thousands of times smaller than a pinhead. It was hotter and denser than anything we can imagine.

•Big bang theory:

• The Universe that we know was born. Time, space and matter all began with the Big Bang. In a fraction of a second, the Universe grew from smaller than a single atom to bigger than a galaxy. And it kept on growing at a fantastic rate. It is still expanding today.

As the Universe expanded and cooled, energy changed into particles of matter and antimatter. These two opposite types of particles largely destroyed each other. But some matter survived. More stable particles called protons and neutrons started to form when the Universe was one second old.

• Over the next three minutes, the temperature dropped below 1 billion degrees Celsius. It was now cool enough for the protons and neutrons to come together, forming hydrogen and helium nuclei.

• After 300 000 years, the Universe had cooled to about 3000 degrees. Atomic nuclei could finally capture electrons to form atoms. The Universe filled with clouds of hydrogen and helium gas.

How universe is changing? • The effect, where there is a change in frequency and wavelength, is called the Doppler effect. It happens

with any wave source that moves relative to an observer.

• This happens with light too. Our sun contains helium. We know this because there are black lines in the spectrum of the light from the sun, where helium has absorbed light. These lines form the absorption spectrum for helium.

• Spectrum of the sun

• When we look at the spectrum of a distant star, the absorption spectrum is there, but the pattern of lines has moved towards the red end of the spectrum, as you can see below.

Spectrum of a distant star

This is called red shift.

• Cosmic Microwave Background radiation

• Scientists discovered that there are microwaves coming from every direction in space. Big Bang theory says this is energy created at the beginning of the universe, just after the Big Bang, and that has been travelling through space ever since.Big Bang theorists are still working on the interpretation of this evidence.

Evidence InterpretationThe light from other galaxies is red-shifted.

The other galaxies are moving away from us.

The further away the galaxy, the more its light is red-shifted.

The most likely explanation is that the whole universe is expanding. This supports the theory that the start of the universe could have been from a single explosion.

Cosmic Microwave BackgroundThe relatively uniform background radiation is the remains of energy created just after the Big Bang.