Which direction are we looking? North Are the stars moving clockwise or counter-clockwise? Counter-clockwise (E to W)

Kitt Peak Observatory, Arizona; altitude: ~7000 feet

Annual or Seasonal Motion The Earth makes one complete orbit (360o) in 365 days, or approximately 1o / day. The closer the planet to the Sun, the shorter the orbital period. Mercury ~ 0.25 “Earth year” Mars ~ 1.9 “Earth years” Pluto ~ 250 “Earth years”

What causes the seasons? The Earth is not closer to the Sun in the summer!! What causes the seasons? The Sun is hotter in the summer. The Earth is tilted more in the summer. The Earth is closer to the Sun in the summer. The Sun’s light rays are more concentrated during the summer. Answer: d

Earth is tilted 23.5o on its axis tilted with respect to the Earth’s orbital plane - N. Summer: N. hemisphere tilted toward Sun - N. Winter: S. hemisphere tilted toward Sun

The Earth’s tilt is responsible for the seasons. The NCP always points to Polaris.

The DIRECTNESS of the rays is what causes the seasons to occur summer (N. Hemisphere) – more VERTICAL RAYS winter (N. Hemisphere) – fewer VERTICAL RAYS Fact 1: Earth’s orbit is nearly circular: Earth-Sun distance only changes by 3% over the year. Fact 2: Because the Earth’s orbit is slightly elliptical, the Earth is actually closest to the Sun during January!!

“On Earth”, we observe changes over the course of the year due to the tilt of the Earth on its axis northeast southeast Sunrise

Position of sunrise and sunset changes due to the orientation of the Earth with the Sun Sun rises North of East in Summer Sun sets North of West in Summer Sun sets South of East in Winter Sun sets South of West in Winter