The Solar Constant
and
Solar Incidences

The solar constant is the amount of solar radiation incidence that is received at a distance of 1 astronomical unit (AU) from the Sun. It is presently calculated as being 1,366 W/m2.

Due to the fact that the earth rotates around the sun and it's distance depends on the time of year, the actual direct solar incidence that Earth receives varies from 1,412 W/m2 in January to 1,321 W/m2 in July.

If you want to calculate specific solar incidences for a certain distance in AU's, use the following formula:

Calculating Solar Incidences for the Solar System:

E = C • (1/Distance)2

Where

E: Incidence in W/m2.
C: Solar Constant at 1 AU (1,366 W/m2)

EXAMPLE: What is the solar incidence at 1.5 AU?

1,366 • (1/1.5)2 = 607 W/m2

Below is a table of solar incidences for mission planning, whether for spacecraft thermal control to spacecraft power generation.

Planets, Distances and Incidences

Planet

Mean Radius
(AU)

Solar Radiation Incidence
(W/m2)

Mercury

0.387

9,121

Venus

0.720

2,635

Earth/Moon

1.000

1,366

Mars

1.520

591

Asteroid Belt

2.500

219

3.5 AU Distance

3.500

112

Jupiter

5.190

51

7 AU Distance

7.000

28

Saturn

9.510

15

Uranus

19.000

4

Neptune

30.000

1.5

Pluto

39.480

0.9