Institute of Astronomy


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Nuclei of Atoms

Published on 14/03/2011 

How are protons and neutrons combined to create the nucleus of an atom?

Protons and neutrons are not a fundamental particles, rather they made of three particles known as quarks bound together.

In addition to electrical forces from their charges, quarks also feel the strong force, another of the fundamental forces. It is this force that binds together quarks into neutrons and protons and also holds the protons and neutrons together in the nucleus of an atom. As the name suggests, this is a very strong force - it is able to hold together protons in a nucleus despite their like charges repelling each other and remarkably, the further apart you move the particles, the stronger the force gets between them!

Twinkling stars

Published on 28/02/2011 

Why do stars twinkle and planets do not?

In fact, both stars and planets twinkle! The twinkling is due to the turbulent air in the Earth's atmosphere, blurring and distorting the image of the star. The twinkling therefore has more of an effect nearer to the horizon, where the light must travel through more of the densest parts of the Earth's atmosphere. You can see this for yourself! Compare the twinkling of a star near the horizon (such as Sirius), and one close to zenith (straight up). Objects such as the Sun, Moon and the planets are called extended sources, because the light is emitted from a disc. Objects such as distant stars are called point sources, because they appear to be a point as they are very far away. In fact, the light from extended sources can be thought of as many point sources spread over an area. The turbulent air in the atmosphere causes a point source to appear to move around on the sky ever so slightly. However if we spread many point sources over the face of the planet, all point sources move around, but we do not notice a change in the total light from the object.

The brightest star

Published on 28/02/2011 

What is the brightest star in the night sky?

We believe our galaxy, the Milky Way, contains roughly 200 THOUSAND MILLION stars (that is, 200,000,000,000). However, if you were to count the number of stars in the night sky with a naked eye, you would only be able to count about 6,000. Besides our star, the Sun, the brightest star in the night sky is Sirius, in the constellation Canis Major (the “Big Dog”). Sirius is almost twice as bright as the next brightest star, Canopus, in the constellation Carina.

The colour of the sky

Published on 28/02/2011 

Why is the sky blue during the day then red at sunset?

Light from the Sun contains all colours of the rainbow. When we look directly at the Sun, we see all of the light from it, so it appears white or a faint yellow. Particles in the Earth's atmosphere scatter shorter wavelength (bluer) light more than the longer wavelength (redder) light due to a process called Rayleigh scattering. During the day, the entire sky looks blue, as we are seeing the light that has been scattered towards us from all directions. However, when the Sun's rays travel through more of the denser part of our atmosphere (at sunrise and sunset) it appears red, as more of the blue light is scattered.

Supporting life on other planets

Published on 28/02/2011 

What is the Habitable Zone?

The habitable zone is a region around a star where an orbiting planet could host liquid water. It is sometimes also known as the Goldilocks Zone, because the planet must not be too close to the star (where any water will vapourise) and not too far from the star (where water will freeze).