The Big Bang theory

The video below shows the relative sizes of the planets. moons, stars and galaxies in the known universe.

The big bang

Once the observation was made that everything in the universe appears to be moving away from everything else the logical conclusion was that all matter must have started out closer together.

The idea that everything started from one point in the universe and has been expanding ever since became known as the Big Bang.

The term originated during a radio broadcast in 1949 in which the astronomer Fred Hoyle was describing this theory of the origin of the universe.

Evidence for the Big Bang theory

The acceleration of galaxies that could be observed from Earth was determined by their Doppler shift. That is the shift in light wavelength due to their moving away from us. An object move towards us exhibits a compression of light waves making it seem more blue. An object leaving us at a great speed shows a stretching of the light waves and seems more red.

This effect is similar to the noise a train makes as it approaches compared to when it is moving away. During the approach the sound waves are compressed and the sound has a higher pitch. When moving away it has a lower pitch due to expansion of the sound waves.

The Doppler effect

The life-cycle of stars

Stars are thought to form from condensed gas being slowly collected by gravity until a critical mass is reached, when the object's gravity is powerful enough to allow the hydrogen atoms to fuse together. Several hydrogen nuclei are fused together in a series of steps forming Helium.

This fusion reaction releases vast amounts of energy.

This is a simplified version. The video below explains about how stars go through different phases during their life cycle.

The life cycle of of stars.

What is a star made of

A star is made of gas, which consists mostly of Hydrogen and helium, the most commonly found elements in the Universe. The gas cloud is so dense its gravity holds it together.

Like the Earth, stars are made of many layers, each with distinctive properties.

The structure of the sun

Stellar classification

Stellar classification, means the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the rainbow of colors interspersed with spectral lines. Each line indicates a particular chemical element or molecule, with the line strength indicating the abundance of that element. The strengths of the different spectral lines vary mainly due to the temperature of the photosphere, although in some cases there are true abundance differences.

The element helium was first discovered by examining the spectral lines of the sun. New coloured lines were discovered in the sun's spectrum that did not correspond to any known element on Earth. For this reason its name is helium, which comes from the Greek word "helios", meaning sun.

The spectrum of helium

The Earth

Our planet

The moon

Classification of rocks

The lime cycle