Jul 21 2014

What are Stars?

Stars are all those little pin points of light in the night sky that slowly move around the sky throughout the year, but what exactly are they? Stars are the furnaces of the universe; a single star is a huge collection of matter that is gravitationally pulling itself together into a sphere and this gravitational attraction causes a fantastic amount of pressure right at the centre of the star. The amount of pressure causes the temperature to rise (when you compress matter it gives of heat) so much that the individual atoms star to move more quickly. The conditions at the centre of the star are perfect for Nuclear Fusion as everything is squashed very close together (pressure) and moving quickly (temperature). This combination of pressure and temperature means that particles or atoms get very close to one another and can overcome the repulsion of the electromagnetic force and fuse together into a larger atom. This is how new elements are produced within stars. Everything around you was originally made in the centre of a star.

“We are all made of star stuff” – Carl Sagan.

But, the mass of the new fused atom is slightly less than the sum of the individual atoms that were fused together. The little bit of mass that is missing is given off when fusion happens in the form of light and heat and it is these two things that we see and feel on Earth on a sunny day.

Star types

There are many different types of stars in our galaxy with different colours, sizes and temperatures. For and example of this look at the constellation of Orion visible in the winter months in the northern hemisphere.

The constellation of Orion

The constellation of Orion

In the top left of Orion you will see Betelgeuse, a red super giant star, and in the bottom right you will see Rigel, a blue super giant star. Using a pair of binoculars or a small telescope you can see the difference in colour yourself. The difference is caused by Betelgeuse having a surface temperature of only about 3,500K but Rigel having a much hotter surface temperature of about 11,000K. Rigel has a lot more mass and therefore the pressure and temperature at it’s core are a lot higher. This causes it to fuse atoms faster and at a higher rate which gives it the higher temperature and when things get hotter they turn bluer, in the case of Rigel, blue-white.

I will be writing more about stars in my next few blog posts as there is much more to tell but I will leave you with one last fact, all the stars you see in the night sky are within the milky way, our own galaxy.

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