# When is it safe to look at the Sun

Home Forums General Discussion Solar eclipses from elsewhere in the solar system When is it safe to look at the Sun

#584558

Light radiating from the Sun follows the inverse square law (ie intensity = 1/d*d)

The benchmark value for the Earth at one Astronomical Unit (AU) from the Sun is thus 1/1*1 = 1.

For Mercury 1/0.3*0.3 = 11. The Sun is more than ten times brighter than on Earth.

For Venus 1/0.7*0.7 = 2. The Sun is around twice as bright as on Earth.

For Mars 1/1.5*1.5 = 0.44. The Sun is less than half as bright as it appears on Earth.

For Jupiter 1/5.2*5.2 = 0.036. The Sun is only around 4% as bright as it appears on Earth.

For Saturn, 1/9.5*9.5 = 0.01. The Sun is only around 1% as bright as it appears from the Earth.

For Neptune 1/30*30 = 0.001. The Sun is only 0.1% as bright as it appears from the Earth.

Solar filters typically reduce light levels by 99.999% (ie allow 0.00001 pu through).

We need to rearrange the inverse square law formula to make distance the object (ie d = sqrt (1/i))

sqrt (1/0.00001) = 316 AU or 29 374 000 000 miles.

At this distance the Sun would subtend an angle of arc tan 865 300/29 374 000 000 = 0.0017 deg. or 6 arc seconds (hopefully I haven’t made any mistakes in my maths).