The life cycle of the Sun has been muddled up below. Look at the pictures and read the text to the side of them, see if you can put the life cycle of the Sun into the right order. Once you think you've got it right uses the links to the side to add the text to the blank area at the bottom, you can then check through your new order. If you think you have got it right you can submit your password and try to get into the extra area, if you get it wrong don't worry hit clear and try a new order.

Image of the Sun taken by the Soho Probe The collapse of the star is balanced first by the fusion of hydrogen generating helium. The first cycle of fusion produces a helium core to the star with a shell of hydrogen fusion around it. The Sun has been in this first fusion process for the last 5 giga years. As long as there is an abundance of hydrogen to fuse in the core of the Sun this is the way that it will stay. Add to below
Hubble Space Telescope image of an area of a nebula as yet to colapse into a star Stars start their lives as part of a large interstellar cloud of hydrogen, along with dusty and gaseous remains of other stars. Over eons the nebula will slowly collapse under its own gravity. The gravitational collapse is balanced by heating due to the loss of gravitational potential energy. The collapsing process is often greatly speeded up by events outside the nebulae such as supernova shock waves and the shielding effects of dust. Add to below
Hubble Space Telescope image of a planetary nebula As these fusion shells increase the density of the outer layers decreases. The formation of the shells is often turbulent and comes in flashes which blows off the outer layers, leaving a star surrounded by rings of glowing gas: this is often called a planetary nebula. The core of the star remains as a white dwarf, no new fusion processes will occur and over the eons the white dwarf will cool and fade. Add to below
This Hubble Space Telescope image of the Wolf-Rayet star. This star is a very rare class of Star, the star is seen going though a violet transitional phase. As the hydrogen is used up the gravitational potential of the star heats up the core until a point where the temperature required to fuse helium nuclei into carbon is reached. The process continues through the elements as the fusion condition for each element are met in the core. Each new fusion process moves the former process out into a shell away from the core, heating up the outer layers of the star and puffing them up to form a red giant. Add to below
Hubble Space Telescope image of a proto star forming out of a nebula

As the gas in the nebula collapses into a proto star an enormous amount of heat is produced, through the loss of gravitational potential energy. The particles at the centre of the proto star gain a massive amount of kinetic energy.

Eventually the density and temperature in the centre of the proto star reaches a point where collisions between particles have enough energy to overcome their repulsive forces and the hydrogen atoms in the core start to fuse into helium, the proto star ignites into a star.

To reach the temperature needed for nuclear fusion the proto star needs to have a mass greater than about one eightieth of the Sun. Below that it will become an inert Brown Dwarf or a large gassy object like Jupiter.

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REF : S0702