- Albedo
(common symbol α: see, e.g.,
Wikipedia:
Albedo:White-sky and black-sky albedo) is usually given as a
decimal fraction.
Albedo can be given in The percentage form in which case it is the decimal fraction form times 100 %. This what the image uses.

In the analysis below, we use symbol α for albedo and the decimal fraction form---and

**NOT**the percentage form. - The displayed land covers are as follows:
- Effective temperature
is a fiducial-value
temperature for a
spherical body (e.g., star,
planet).
It is the temperature the
body would have if it radiated its
non-reflective luminosity
like an exact blackbody radiator.
If the body is approximately a blackbody radiator, the effective temperature is approximately the actual surface temperature, and so is a good characteristic or sort of average temperature. If the body is

**NOT**approximately a blackbody radiator, the effective temperature is still often a useful value for characterizing the body particularly for comparison to other bodies. - We can do a derivation
of a useful formula
for the effective temperature
of planets.
- F = L/(4πr**2) : The formula
for flux from an isotropically radiating
star of
luminosity at
distance r from the star.
It is an inverse-square-law
formula
- P = πR**2*F : The formula for the
power captured by
a planet of
radius R at distance r from the
star.
- f = [P/(4πR**2)]*(1-α) = σ*T_eff**4 : The f is the
average power per unit area
absorbed into the
heat energy
of the planet---the
reflected
electromagnetic radiation (EMR)
is removed by the factor (1-α)---and
we have equated it to the
Stefan-Boltzmann law
for the flux radiated by
a blackbody radiator at
temperature T_eff
which is, of course, the
effective temperature of the
planet.
The Stefan-Boltzmann constant σ = 5.670367(13)*10**(-8) W/*m**2*K**4).

- Solving for T_eff gives
### T_eff = {[L/(16πr**2*σ)]*(1-α)}**(1/4)

or in a fiducial-value formula### T_eff = ( 278.33000 K )* (L/L_☉)**(1/4)*(r_⊕/r)**(1/2)*(1-α)**(1/4) ,

The formula agrees with the one given by Wikipedia: Effective temperature: Planet.

- F = L/(4πr**2) : The formula
for flux from an isotropically radiating
star of
luminosity at
distance r from the star.
It is an inverse-square-law
formula
- Using the above formula, we determine
the following
effective temperatures for
the
inner-Solar-System
planets:
Mercury ☿,
Venus ♀,
Earth ⊕,
Mars ♂.
_______________________________________________________________________ Table: Effective Temperatures for the Inner-Solar-System Planets _______________________________________________________________________ Planet R_orbital_mean α_b T_eff T_eff T_(mean/fiducial) α=0 α_b (AU) (K) (K) (K) _______________________________________________________________________ Mercury 0.387098 0.068 447.4 439.5 100 (night), 700 (day) Venus 0.723332 0.90 327.3 184.0 740 Earth 1.000001018 0.306 278.3 254.0 288 Mars 1.523679 0.25 225.5 209.8 210 _______________________________________________________________________

Note: The α_b is the bond albedo which is the appropriate planetary albedo for calculating effective temperature. - The effective temperature
can only be a crude average temperature
if the planet has extreme day-night
temperature variation like
Mercury.
Recall the Mercury's
synodic day (i.e., solar day)
is 176 days which is almost twice
Mercury's
orbital period 87.9691 days
and almost 3 times its
sidereal rotation period 58.646 days
due
Mercury's 3:2
spin-orbit resonance.
It's a long cold night on Mercury
of ∼ 88 days.
- The effective temperature
departs increasingly from the actual average temperature
with increasing greenhouse effect.
Venus has an extreme greenhouse effect and Earth a moderate one.

- What would be planet's
average temperature with the
greenhouse effect turned off?
That depends on what other counterfactual assumptions you make?

For example, if you turn off the greenhouse effect for Venus, but keep its bond albedo α_b = 0.90, then Venus will have a very low average temperature closely approximating the effective temperature 184.0 K given in the table above.

But Venus's greenhouse effect is caused by Venusian atmosphere which also gives Venus its high bond albedo.

Without the Venusian atmosphere, Venus would probably have a bond albedo similar to that of the Moon 0.136. Then Venus would have probably have an average temperature an average temperature closely approximating the effective temperature 327.3 K given in the table above.

- Because the relatively short
Martian day = 25h,39m,35.244s)
(causing very small
thermal inertia)
very thin Martian atmosphere
(causing very little greenhouse effect)
and
relatively low bond albedo
(which roughly appoximates zero),
Mars's
actual average temperature
closely approximates the
effective temperatures
given in the table above.

Caption: Albedo as a percentage as a function of Earth land cover (i.e., surface type) and cloud type.

Features:

Image link: Wikimedia Commons: File:Albedo-e hg.svg.

Local file: local link: temperature_effective.html.

File: Earth file: temperature_effective.html.