How Does the Sun's Position Affect Gravitational Acceleration on Earth?

[quark001]

If the sun is close to the horizon, calculate the horizontal gravitational acceleration of a rock dropped near the surface of the earth. Do the same substituting moon for sun.

Calculating (vertical) g is easy and one could apply the same method to get the horizontal g if you knew the masses of the sun and Earth and the distance between the sun and the earth. My problem is the value for this distance. What's meant by "close to the horizon"?

 

[voko]

Close to the horizon means the Sun's pull is approximately horizontal.