Our planet

[RichIsnang]

If somebody other civilisation on another planet started to look at the sky in great detail, what would they see coming from earth?

Would all our radio waves and other such electromagnetic radiation be visible across several light years?

Or would our planet just look like a ball of rock

[Spyman]

Can Aliens Find Us?

 

Oct. 23, 2003

by Seth Shostak - Senior Astronomer

 

Bottom line? With radio technology slightly more advanced than our own, Homo sapiens is detectable out to a distance of roughly 50 light-years. Within that distance are about 5,000 stars, all of which have had the enviable pleasure of receiving terrestrial television. And each day, a fresh stellar system is exposed to signals from Earth.

[RichIsnang]

Cool thanks

[questionposter]

Even if a signal was picked up 50 light years outward, it would still take another 50 years to get a response back.

[RichIsnang]

Of course, hence 50 light years

[PerpetuallyConfused]

Assuming that the planet or space ship receiving the light at the other end is not travelling at relativistic speed, i.e. fast enough that time dilation becomes a major issue, then the observer would see everything that a rocket on mars would, except that the light, radio waves and other emitted spectra might be modified on its journey through interstellar space between point A and B, where B is the observer.

 

Such modifications to light are frequent and we use this principle to detect the 'wobble' of a distant star when a planet within its local star system crosses between the star and our telescopes. Using this 'wobble' we are able to detect planets. Also, light 'curves' along gravitationally large objects.

 

If the observer at point B was travelling either towards or away from earth at relativistic speed, then the doppler effect comes into play, stretching or compressing the electromagnetic waves (perceptually) before they are detected by the observer.