The apparent brightness is defined by how much light we get pretty much. The formula is:

This takes into account that the light is spreading out to a sphere that has the surface given by 4πd^2.
We have that d=20 ly and 1 ly is 9.46*10^12 km or 9.46*10^15m.
Hence, d=20*9.46*10^15=189.2 *10^15 m
Now, we can substitute the d value and calculate that L=<span>8.45184*

W/m^2</span>
Answer:
Seafloor spreading is a geologic process in which tectonic plates—large slabs of Earth's lithosphere—split apart from each other.
Explanation:
Seafloor spreading is a geologic process in which tectonic plates—large slabs of Earth's lithosphere—split apart from each other.
Answer:
There isn´t other planet on which we could survive unprotected
Explanation:
Still no other planet has been found that has an atmosphere capable of retaining oxygen and decreasing solar radiation so that the person does not need as much oxygen equipment as a special suit to avoid the different types of raciations that can reach the planet .
It is also believed that it is possible to find on a future planet similar to Earth in which you can live without protection.