Earth always stays tilted in same direction. Daylight is longer in summer (sun"s path to sky is longer) and shorter in winter (sun"s path to sky is shorter) Sunlight angle hits diff parts of earth at steeper angle during summer and shallower angle during winter. As earth orbits sun, axis is either pointing towards or away from sun. Takes earth time to warm up and cool down. Why it"s warmer a month after summer solstice and cooler after winter solstice. Summer in the north, winter in the south. June solstice: moment when northern hemisphere is tipped most directly toward sun and receives most direct sunlight; first day of summer. Axis neither pointed towards or away from sun. Neither hemisphere is getting more sunlight than the other. Fall in the north, spring in the south. September equinox: moment when northern hemisphere goes from being tipped slightly towards. Sun to slightly away from sun; first day of fall.