Why the earth is closer or further away from the sun during different times of year

Because of Earth's axial tilt (obliquity), our planet orbits the Sun on a slant which means different areas of Earth point toward or away from the Sun at different times of the year. Around the June solstice, the North Pole is tilted toward the Sun and the Northern Hemisphere gets more of the Sun's direct rays.

No it is an oblate spheroid apparently

Round it to the nearest tenth