Orbit Seasons
The Earth's orbit around the Sun is elliptical, or egg-shaped. At certain times of the year, the globe is closer to the Sun than at others. This occurs during the spring and summer months in the northern hemisphere, which is why it is warm during April to September.
Axis Seasons
The relative position of the Earth to the Sun in terms of the planet's natural tilt is also important. During the summer periods, the northern hemisphere is pointing more directly at the Sun during daylight hours, so the temperature is naturally higher. This is why the Sun rise in summer time is higher in the sky, while during the winter it rises less above the horizon. The southern hemisphere is always pointing directly at the Sun, which is why annual temperatures south of the equator are higher than the north.
Axis Time
As the Earth rotates on its axis, places on the Earth go from being shadowed from the Sun, night time, to facing the Sun, daytime. If the Sun rises in New York at 6 am, it is still 3 am on the West Coast as it is still sheltered from the sunlight. If the entire world operated on the same time, working hours in half the world would be in darkness. The International Date Line, situated off the west coast of the U.S., keeps the world operating on the same day. By crossing the International Date Line, you essentially travel forward in time to the next day. This sensation of time change is experienced best as jet lag after a long airplane flight.
Orbit Time
As the Earth rotates around the Sun, daylight hours get longer as the northern hemisphere points more directly at the Sun. This does not lead to a change in the time, but an extension of daylight and a reduction in night time.