Now consider the statements in Part A that are inferred from models. A solar model is used to calculate interior conditions based on certain "known" characteristics of the Sun, such the Sun’s total mass. How do we know the Sun’s mass?
A) We infer the mass from a model of the Sun.
B) We first measure the Sun's size and density, then use these measurements to calculate the Sun’s mass.
C) We can calculate it by using the law of conservation of energy with the measured amount of light that the Sun emits.
D) We can calculate it by applying Newton's version of Kepler's third law with Earth's orbital period (1 year) and Earth’s average distance from the Sun (1 AU).

thermal energy is the answer

scattering of light by tiny particles in air to produce the colors we see on sky, is dependent on the following factors:

(i) wavelength of light

(ii) size of the scattering particle  

(iii) distance traveled by light through the atmosphere.

according to rayleigh's law of scattering, the amount of scattering is inversely proportional to the fourth power of its wavelength. shorter the wavelength, greater is its scattering. hence violet/blue light is scattered more than red.

sun's light is a composite light ( visible light) with wavelengths in the range 400 nm (violet) to 700 nm (red). as sunlight passes through our atmosphere, the molecules of air scatter light according to their wavelengths. during sunrise and sunset, the sun's position is below the horizon. hence light from the sun travels a greater distance in the atmosphere when compared to its position a noon.

as sunlight enters the earth's atmosphere, blue light is scattered away and at the end of its journey in the sky, only red and orange wavelengths remain in the beam.

hence at sunrise and sunset, the sky appears reddish orange.