What is the relationship between the direction of the electric field lines and the change in electric equipotential?

Direction of the electric field lines means direction of lower electric potential.

Explanation:

The direction of the electric field tells us the direction to which the electric potential gets smaller. This is because we use a positive charge as a probe to define everything. If this charge goes against the electric field (lets imagine produced by another positive charge) we realize that work must be done to achieve this, thus we are increasing in electric potential. The other way around: going with the electric field would be what this probe positive charge would do, which is falling in the potential, thus going to lower potential values.

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.