Why are the hours of night and day different on Earth and does this happen on other planets?

While the change between day and night results from the Earth's rotation on its axis, the changing lengths of day and night depend on where you are on Earth and the time of year.

While you don't feel it, the Earth rotates on its axis once every 24 hours, taking us all with it. When we are on the side of the Earth facing the sun, we have daylight. As the Earth continues to spin, we move with it to the side farthest from the Sun, and we have night.

And if we were looking at the Earth from the top of the North Pole, we could see the Earth spinning counterclockwise, and we'd see daylight and darkness sweeping across the globe from east to west.

While the change between day and night results from the Earth's rotation on its axis, the changing lengths of day and night depend on where you are on Earth and the time of year. The hours of the day are also affected by the tilt of the Earth's axis and its path around the Sun.

Why does the length of the Earth's day change during the year?

Although a solar day is 24 hours, it does not contain 12 hours of daylight and 12 hours of night each day. We will notice that the days are shorter in winter than in summer. This is due to the tilt of the Earth's axis 23.5 degrees.

As the Earth moves around the sun during a year, the northern hemisphere tilts toward the sun in summer, making the day longer than the night. And in winter it is reversed. As the Earth tilts away from the sun, the night becomes longer. In spring and autumn, the inclination is not towards or away from the sun but somewhere in between, so the day and night are the same at these times of the year.

The actual number of hours of daylight on any given day of the year varies from place to place as well, and locations around the Earth's equator receive about 12 hours of light each day.

In contrast, the Arctic receives 24 hours of daylight for a few months in the summer and total darkness for several months in the winter, and these two annual periods of light and darkness are separated by a long sunrise and a long sunset.

These differences are due to the Earth's rotation around its tilted axis by 23.5 degrees. When the Earth revolves around the Sun, its tilted axis always points in the same direction, almost directly toward the North Star Polaris. So, throughout the year, different parts of the Earth get a different amount of direct sunlight.

What caused the tilt of the Earth?

A long time ago, it was believed that a large object called "Theia" had hit the Earth and made it unstable. So instead of spinning with its axis straight up and down, it tilts a little more.

That strike sent a huge amount of dust and debris from the Earth into orbit, creating a very large hole on Earth. Most scientists believe that these ruins are what formed our current moon.

The difference between a solar day and a sidereal day

The Earth rotates around itself once every 24 hours from the perspective of the solar "solar day", and it rotates once every 23 hours, 56 minutes and 4 seconds from the perspective of the stars, "the astronomical day".

A solar day is the time it takes the Earth to rotate exactly once so that the sun appears in 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 for one revolution of the Earth on its axis is a little shorter, about 23 hours and 56 minutes. Astronomers discovered this by observing the time it takes for a star to appear in the same place in the sky the next day, and they called this day "astronomical" or "stellar".

The Earth's rotation around itself slows down over time, knowing that the day in the past was shorter than it is now, due to the effects of the tides caused by the moon on the Earth's rotation.

The longest and shortest days of the year

Solstices are the positions of the Earth's orbit that determine the longest and shortest days of the year. In the northern hemisphere, the winter solstice has the shortest day, and after that the daylight hours are longer. In the northern hemisphere, the summer solstice falls on the longest day, after which the daylight hours become shorter.

Winter solstices can also be called the month in which they occur. For example, the June solstice is the point in 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.

Location on the ground

Your position on Earth in relation to the equator also affects the number of hours of daylight you get on a solar day. For example, during the summer in the northern hemisphere, the hours of daylight increase in the far north of your destination; At this time, the North Pole gets a little dark at night.

In winter, the days are shorter the further north you are. On the equator, day and night are always equal, regardless of the season, and this is why it is called the equator.

Do other planets have day and night?

Yes, all the planets in our solar system rotate on their axes, and thus have cycles of day and night.

Some planets rotate faster than Earth and some rotate slower. Mars has a day and night cycle similar to Earth. While Mars rotates on its axis once every 24.6 hours, Venus rotates on its axis once every 243 Earth days, which is slightly longer than it takes Venus to revolve around the sun.

The day and night cycle of Mercury is more complex, as Mercury rotates one and a half times during every single orbit it completes around the sun. Because of this, Mercury's day, from sunrise to sunrise, is 176 Earth days long.

The larger planets rotate faster on their axis. Jupiter rotates once every 10 hours, Saturn rotates once every 11 hours, and Neptune completes its rotation in 16 hours. While Pluto, at the farthest point in our solar system, rotates on its axis once every 6.4 days.

Length of day and night on other planets

Other planets also experience these changes in the length of day and night hours, because they are also tilted on their axes. Each planet's axis tilts at a different angle. Jupiter tilts only 3 degrees, so its change in the length of the day and night as it moves around the sun is less severe than it does on Earth. Neptune's axis is tilted 30 degrees, so changes in day and night will be more severe on Neptune than on Earth.

While Uranus presents an interesting case because the tilt of its axis is more extreme, 98 degrees, this means that the north pole of Uranus is pointed toward the sun during the arctic summer. The Antarctic is in complete darkness.

During the arctic winter, about 42 years after Earth, the south polar axis is turned to the sun and the north polar region is in complete darkness. During spring and fall, when its axis is perpendicular to incoming sunlight, Uranus goes through a 17-hour day and night cycle as it rotates on its axis.