Author Question: The Sun radiates at an effective temperature of 5780 K and has a radius of about 696,000 km. ... (Read 115 times)

cmoore54 · **on:** Jul 14, 2018

The Sun radiates at an effective temperature of 5780 K and has a radius of about 696,000 km. Remembering that 1 AU = 149,600,000 km, derive the approximate value of the solar flux at Earth's orbit. Compare your answer with the value given in the text.

What will be an ideal response?

Question 2

How do the results of (d) compare with the magnitude of the greenhouse effect on Earth?

What will be an ideal response?

Kaytorgator · **Reply #1 on:** Jul 14, 2018

Answer to Question 1

Given:
Effective temperature of Sun: Te= 5780 K; Te= ((S/4)(1-A))1/4
Radius of Sun: r 0= 696,000 km
1 AU = 149,600,000 km
Solar Flux (S): S0= T04
S0= (5780)4
S0= 6.328 107 W/m2

S = S0(r0/r)
S = 6.328 107 (696,000/149,600,000)2
S = 6.328 107 (2.164 10-5)
S = 1370 W/m2

Answer to Question 2

Venus' atmosphere contains 90 bar of CO2, and it consequently has much more of a greenhouse effect than Earth, causing a temperature increase of 510.3 K compared to 33 K (more than 15 times the magnitude). Mars, on the other hand, has a significantly smaller a greenhouse effect than Earth, which only raises its temperature by 5.5 K. Mars' greenhouse effect is low because its atmosphere is thin (6 mbar) the cold temperature means that there is very little H2O in its atmosphere. This gives us some insight into the composition and size of the atmospheres of Venus and Mars.