'The Guessing Game.''



While the search for life continues in our own solar system astronomers are also looking for life beyond our own galaxy.

There are billions of stars similar to our own sun in the milky way. Might they have planetary systems like ours on which life could begin?

Astronomers now know that planets are a bi-product of star birth, and have detected the presence of 'extra solar' planets.

Based on our current understanding of our own planetary system astronomers can begin to predict how common life is likely to be in the universe.

The Milky way

Unless a method for faster than light travel or communication is devised It is likely that if we are going to have any communication with another civilisation it will be limited to our own galaxy, the Milky way. Other galaxy's are so far away that it would take millions of years for a signal to reach us!

The Milky way is huge!

It is so wide that it would take 100,000 years for a radio wave traveling at the speed of light (186,000 miles per second (300,000 km per second)) to get from one side to the other.

The Milky way contains over 200 billion stars. It is also estimated that there are 50 million stars within 1000 light years of our own sun.

As suns go; our sun is a very ordinary, middle aged, middle class star which is situated about 2/3rds out from the galactic centre. There are millions of similar suns spread throughout our galaxy alone.

The drake equation.

Frank drake American astronomer and founder of S.E.T.I devised an equation to estimate the number of civilisations capable of communicating in our own galaxy (the Milky way).

The equation looks like this.

N=R* X Fp x Ne x F1 x Fi x Fc x L

Breaking down the equation


Number of civilisations capable of communicating in our own galaxy (the Milky way).


Rate of star birth - how many stars are born. Astronomers generally agree that this is around 10 per year in our galaxy.


The percentage of new stars that form planets.


The percentage of those planets that are capable of supporting life due to being the right distance and size from their star.


The percentage of those planets that have life.


The percentage of planets that have ''intelligent'' life-forms.


The percentage of ''intelligent'' life-forms that have developed the capability to communicate with other civilisations.


The percentage of civilisations able to exist long enough to be able to potentially send and receive signals.

The SETI Simulation.

In this simulation which is based on Frank Drakes equation you estimate how many alien civilisations in the Milky way are trying to send or receive messages across the void of space.

Starting with question 1 work your way through to question 6. When you have answered all the questions you can see how many communicating civilisations there might in are in our galaxy.

The figures available for calculation in questions 1- 5 of this simulation are limited to 0.1%, 1%, 10% and 100% depending on the question type. For example question one asks 'What is the chance of a newly born star having planets'. Because scientists are uncertain of the facts the choices given here are 10% or a 100%. 10% means that one in ten of all newly formed stars have planets; 100% means that all newly formed stars have planets.

Its up to you to choose which figure you think is closest to the truth. Once you have decided, click on your choice to move on to the next question.

If you were working on paper then you could supplement the percentages shown in the simulation for an exact figure.

For example if you think that the proportion of habitable planets formed around a star is 10% you would write Ne=0.10 into the equation.


When answering the questions try to take an informed approach to your decision. Being strictly optimistic or pessimistic will invariably give the same answers each time.

One Galaxy one planet.

If you take a pessimistic approach your answers will steer you to the left hand side of the simulation resulting in a final answer of 0.01 meaning that there is only one communicating civilisation in 100 galaxies. This would mean that we are the only communicating civilisation in the Milky way; and we would need to look outside our own galaxy for other civilisations.

Closer than you think!

Talking an optimistic view will steer you to the right of the simulation resulting in millions of communicating civilisations in the Milky way. For example if your choices indicate that there are 10 million civilisations spread evenly throughout our galaxy, they would lie approximately 100 light years apart. This would mean that there is a possibility of first contact within 100 years.