What Causes the Day/Night Cycle on Earth

What Causes the Day/Night Cycle on Earth

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The change between day and night is caused by the rotation of the Earth on its axis. If the Earth did not rotate as it does, the day/night cycle would be very different or possibly even nonexistent. The changing lengths of days and nights depends on where you are on Earth and the time of year. Also, daylight hours are affected by the tilt of the Earth's axis and its path around the sun.

Length of a Rotation

A solar day, 24 hours, is the time it takes for the Earth to rotate exactly once so that the sun appears at the same place in the sky the next day. However, the Earth is also moving around the sun, and this movement makes measuring the day somewhat complicated. The actual time of one Earth rotation is a little shorter – about 23 hours and 56 minutes. Astronomers discovered this by observing the time it took for a star to appear in the same place in the sky the following day, and they called this a sidereal day.

Longer and Shorter Days

Although a solar day is 24 hours, not every day has 12 hours of daylight and 12 hours of night. Daytime is shorter in winter than in summer. This is because the Earth’s imaginary axis isn’t straight up and down, it is tilted 23.5 degrees. As the Earth moves around the sun during a year, the northern half of the Earth is tilted towards the sun in the summer, making daytime longer than night. In winter, this reverses; the earth tilts away from the sun and nighttime becomes longer. In the spring and fall, the tilt is neither toward or away from the sun but somewhere between, so day and night are more the same at these times of the year.

The Solstices

The solstices are the positions of the Earth's orbit that mark the longest and shortest days of the year. The winter solstice in the Northern Hemisphere is the shortest day, after which daylight hours grow longer. The summer solstice in the Northern Hemisphere falls on the longest day, after which daylight hours become shorter. The solstices can also be named for the month in which they occur. For example, the June solstice is the point in the Earth's orbit where the North Pole faces the sun. In the Northern Hemisphere, the June solstice is the longest day of the year. In the Southern Hemisphere, the June solstice is the shortest day of the year.

Position on Earth

Your place on the Earth relative to the equator also affects the number of daylight hours you get in a solar day. For example, during summer in the Northern Hemisphere, daylight hours increase the farther north you go; at this time, the Arctic gets very little nighttime darkness. In the winter, daytime is shorter the farther north you go. The seasonal changes in daylight hours are small near the equator and more extreme close to the poles.
What Causes the Day/Night Cycle on Earth? | Sciencing

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Revolution:

⦁ The second motion of the earth around the sun in its orbit is called revolution. It takes 365¼ days (one year) to revolve around the sun.
⦁ Six hours saved every year are added to make one day (24 hours) over a span of four years.
⦁ This surplus day is added to the month of February. Thus every fourth year, February is of 29 days instead of 28 days. Such a year with 366 days is called a leap year.

Rotation of Earth

⦁ Earth rotates along its axis from west to east.
⦁ It takes approximately 24 hrs to complete on rotation.
⦁ Days and nights occur due to rotation of the earth.
⦁ The circle that divides the day from night on the globe is called the circle of illumination.
⦁ Earth rotates on a tilted axis.
⦁ Earth’s rotational axis makes an angle of 23.5° with the normal i.e. it makes an angle of 66.5° with the orbital plane. Orbital plane is the plane of earth’s orbit around the Sun

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⦁ The 5 Reasons To Keep Daylight Saving Time Have No Science To Back Them Up:

Daylight Saving Time improves safety. Does additional daylight reduce traffic accidents? You might think so, since driving in the daylight seems safer than driving at night. But the science says otherwise. The day after we "spring forward" and "fall back" both see an increase in fatal traffic accidents, which has been verified to be significant at about the 8% level. There is no corresponding decrease to balance it out. Meanwhile, workplace accidents and heart attacks are both more common in the week after the time change, too. Daylight Saving Time actually causes more deaths, rather than reducing them.
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