The Atmosphere

Why is there life on Earth and not on any other planet as far as we know?

There are 3 main reasons:

• The temperature of the Earth (other planets are too hot or too cold)

• The abundance of surface water

• We have an atmosphere that sustains life.

What is the average temperature of Mercury, Venus and Mars?

What other planet has water been discovered on?

Other planets have atmospheres but they are all highly poisonous to both animal and plant life. Our atmosphere has evolved over billions of years.

Compared to the size of the Earth the atmosphere is very thin. It is made up of different layers.

What does the ozone layer protect us from?

How have humans damaged the ozone layer over the last 50 years?

Light from the Sun is white. It contains all the colours of the visible spectrum ROYGBIV. When this light passes through gas molecules the colours with a longer wavelength (ROYG) more or less pass straight through. Colours with a shorter wavelength (BIV) are absorbed by gas molecules and then reemitted but in any direction. This process is called Rayleigh scattering.

Unless we look directly at the Sun we do not see the light which has NOT been scattered. We only see the scattered blue light.

Sunrise and sunset is often red because light from the Sun has to travel through much more atmosphere to get to us when the Sun is low in the sky. All the blue that was in this light has been scattered and only the red light remains.

pic   Ian Britton - Freefoto.com

Draw a diagram to explain why sunlight has to travel through more atmosphere to get to us at sunrise and sunset.

The Atmosphere and astronomy

When it comes to making detailed observations of the sky the Earth's atmosphere just gets in the way. Just as a diver struggles to see through murky water our view of the stars is blurred by the atmosphere, especially in areas where there is a significant amount of chemical and light pollution. Stars near to the horizon are often invisible because of light pollution, an effect known as extinction.

Skyglow
This is an orange yellow glow above a city of town. It is caused by light which is emitted directly upwards where it then scatters. It makes astronomy anywhere near a city almost impossible, e.g. The Milky Way is just about invisible.

pic   petfishtank.com	pic  Ian Britton - Freefoto.com	pic  NASA
Blimey, where are all the fish?	Not the best place for an observatory	NOT a very good view of the stars
pic  NASA	pic  NASA	pic  NASA
The Gemini South telescope in Chile	The Mount Palomar Observatory in California	The Hubble Space Telescope

Many large telescopes have been built at altitude, e.g. on top of mountains. The higher up you are the less atmosphere you have to look through. They are also built in remote areas where the effects of human pollution are minimised. The Hubble Space Telescope orbits the Earth above the atmosphere. For this reason its pictures are much better than anything achieved with ground based telescopes.

As well as optical astronomy humans also interfere with radio astronomy. radio communications interfere with the very faint radio signals from distant stars and galaxies.

List all the forms of pollution that interfere with astronomy.

Where would be the worst and the best place in the UK to build a large optical telescope?