# Can I see the light from 10 million km away?

If light is switched ON, only for a second, and the distance between the observer and the light source is 10 million kilometers, can I still see the light spark?

For example, let's assume that the source is the Sun and the observer is a human eye.

-
At only 10 million kilometers from the Sun, no human could survive. Also there are some technical difficulties with turning the Sun on for just a second (actually the initial problem is with turning it off first). – Marc van Leeuwen Aug 26 '14 at 6:57

## 2 Answers

Yes it can be seen, given that you do not get much noise and that your sensor is sensitive enough for it to be able to detect the signal. As you have not specified anything about the light not much can be concluded, more than that it depends on the sensor, the transmitter and the noise from everything else.

-

To provide some further Information: The Intensity of the (ballistic) Light is described by Beer-Lambert law, so it is exponentially decaying.

$I=I_{0}e^{-\mu_{e} x}$ where $\mu_{e}$ is known as extinction coefficient. It is the sum of the absorbtion and scattering coefficent. $\mu_{e}=\mu_{s}+\mu_{a} = \frac{1}{l_{s}} + \frac{1}{l_{a}}$

So you have to know the Intensity of your lightsource, the coefficient (which depends on frequency, for the atmosphere some wavelengths are strongly scattering and for others the atmosphere is nearly transparent) an the sensibility of your detector and the Intensity of the background should be lower than the intensity of your source.

Now you have all the tools you need to find your awnser.

-