The flux of solar radiation entering the earth’s atmosphere {measured at the top of the Thermosphere} is called the ____ .

Question

BlackTom AI · Accepted Answer

Solar constant is defined as the solar electromagnetic energy flux (irradiance) received per unit area at the mean distance of the Earth from the Sun (top of the atmosphere, typically taken at about the thermosphere). It is expressed in watts per square meter (W/m^2).

Relevant concepts:
- Radiative flux (irradiance): power per unit area from a source.
- Solar luminosity (L☉): total power emitted by the Sun.
- Geometrical dilution: flux at distance d is L☉ spread over a sphere of area 4πd^2, so S = L☉ / (4πd^2).

Step-by-step reasoning and calculation:
1. Use the formula S = L☉ / (4πd^2).
2. Insert typical values: L☉ ≈ 3.828 × 10^26 W and d = 1 astronomical unit (AU) = 1.496 × 10^11 m.
3. Compute the spherical area factor: 4πd^2 = 4π × (1.496 × 10^11 m)^2 = 4π × 2.238 × 10^22 m^2 ≈ 2.8127 × 10^23 m^2.
4. Divide luminosity by area: S ≈ (3.828 × 10^26 W) / (2.8127 × 10^23 m^2) ≈ 1361 W/m^2.

This value (about 1361 W/m^2, historically often quoted as ~1367 W/m^2 before more precise measurements) is the standard definition of the solar constant: the mean solar irradiance at the top of Earth’s atmosphere.

Why the other options are incorrect:
- Atmospheric constant: not a standard term; atmosphere does not have a single constant flux analogous to the solar constant.
- Temperature constant: unrelated; temperature is not a radiative flux measured at the thermosphere.
- Earth constant: not a recognized physical quantity for incoming solar flux.

Therefore, the correct answer is Solar constant, matching the provided answer.

The flux of solar radiation entering the earth’s atmosphere {measured at the top of the Thermosphere} is called the ____ .单项选择题

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