1) the sun’s centre is 2,872,500,000 km from uranus’ centre, the earth’s orbital radius is 149,600,000 km, and the sun’s radius is 695,990 km. uranus has a diameter of 51,118 km.

a) calculate the closest distance between the sun’s surface and uranus’ surface, then compare this to the distance between uranus and sun centres. then explain why astronomers generally use the centre-centre distance when talking about distances between astronomical objects.

b) suppose that you are orbiting uranus and observe an eroded crater basin on the earth that subtends an angle of 0.150 seconds of arc, when the earth and uranus are on the same side of the sun. use the small angle formula to determine the size of the crater in kilometres.