How Days And Nights Are Formed?

Earth is about 12,000 km (about 7,000 mi) in diameter. As it revolves, or moves in a circle, around the Sun, Earth spins on its axis. This spinning movement is called rotation. Earth’s axis is tilted 23.5° with respect to the plane of its orbit. Each time Earth rotates on its axis, it goes through one day, a cycle of light and dark. Humans artificially divide the day into 24 hours and then divide the hours into 60 minutes and the minutes into 60 seconds. Earth revolves around the Sun once every year, or 365.25 days (most people use a 365-day calendar and take care of the extra 0.25 day by adding a day to the calendar every four years, creating a leap year). The orbit of Earth is almost, but not quite, a circle, so Earth is sometimes a little closer to the Sun than at other times. If Earth were upright as it revolved around the Sun, each point on Earth would have exactly 12 hours of light and 12 hours of dark each day. Because Earth is tilted, however, the northern hemisphere sometimes points toward the Sun and sometimes points away from the Sun. This tilt is responsible for the seasons. When the northern hemisphere points toward the Sun, the northernmost regions of Earth see the Sun 24 hours a day. The whole northern hemisphere gets more sunlight and gets it at a more direct angle than the southern hemisphere does during this period, which lasts for half of the year. The second half of this period, when the northern hemisphere points most directly at the Sun, is the northern hemisphere's summer, which corresponds to winter in the southern hemisphere. During the other half of the year, the southern hemisphere points more directly toward the Sun, so it is spring and summer in the southern hemisphere and fall and winter in the northern hemisphere.

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Earth's Relative Motion

Earth moves in two basic ways: It turns in place, and it revolves around the Sun. Earth turns around its axis, an imaginary line that runs down its center through its North and South poles. The Moon also revolves around Earth. All of these motions produce day and night, the seasons, the phases of the Moon, and solar and lunar eclipses.