1. The Drake Equation Calculating the possibility of life

2. A 360º photo of the Milky Way seen from Death Valley, USA. Image and more details may be found at http://antwrp.gsfc.nasa.gov/apod/ap070508.html

3. Is there life out there? Since the 1960’s astronomers have been trying to work out the probability of contacting extra-terrestrial life. To work out the overall probability we need to ‘guestimate’ the probability of a number of factors occurring.

4. R*,the rate of formation of stars in our galaxy

5. fp, the fraction of stars that have planets around them

6. n e, the number of suitable planets in each planetary system

7. f l the fraction of suitable planets which develop life

8. f i the fraction of life-bearing planets which develop intelligent life

9. f t the fraction of intelligent life bearing planets which develop technology

10. L, the length of time the civilisation releases signals into space What if they’ve already tried to contact us and we missed the call?

11. The Drake Equation To work out the number of civilisations in our galaxy with whom we might have a hope of communicating we multiply all these factors together.

12. Different astronomers and cosmologists use different values for each of these factors. However, it is generally thought that there is a finite chance of contacting extraterrestrial intelligent beings.