Rotation Earth

The Earth rotates in space in front of the Sun and in 24 hours it makes a complete revolution on itself, around a north-south axis.

In the cover  you can see an image of the Earth rotation   Credit: web “vecteezy.com”

Every 24 hours (every 23 h 56 minutes 4 seconds), the Earth makes a complete revolution around an ideal axis that passes through the poles.

It rotates in a west-east direction, in a direct direction (counter-clockwise), producing the impression that it is the sky that revolves around our planet.

This movement, called rotation, is due to the succession of days and nights, with day being the time when our horizon is illuminated by the Sun, and at night when the horizon remains hidden from the sun’s rays.

Earth
Earth rotation

At the equinoxes, the Earth’s axis of rotation is perpendicular to the Sun’s rays, which fall vertically on the equator

The time it takes for the Earth to make one complete revolution around its axis is one day.

The Earth rotates in space in front of the Sun and in 24 hours it makes a complete revolution on itself, around a north-south axis.

This results in 12 hours of sun (day) and 12 hours of darkness (night). This is in broad lines.

Actually, the length of day and night depends on other factors. Also, the perception we have is that it is the Sun that moves around the Earth.

If we observe the sky for a long time, we see that all the stars are moving towards the West.

There is not a single star that has moved in the opposite direction, towards the East. Furthermore, they all appear to have traveled an equal arc magnitude. Each star travels a 15º arc in one hour.

Now we know that this is only apparent, but in the past it was considered that all the stars were firmly installed in a kind of dome called “firmament”. As it was believed, the entire sky rotated around the Earth.

It’s easy and rewarding to get a circumpolar photo image. To do this, you have to prepare a photographic camera installed on a tripod and focus it towards the celestial pole.

Stars
Stars Crédito: Daniel López, astrophotographer at the Instituto de Astrofísicca de Canarias

The shot should be done with the shutter open for two to three hours. This is what is called “long-term shot“. In this way, each of the stars comes out “moved”. They all apparently describe circles around the pole. Each star travels a 15-degree arc in one hour.

As you have to leave the camera on a tripod for so many hours, you run the risk of a gust of wind knocking the tripod to the ground. You have to tie it well.

The rotation of the Earth on its axis gives the impression that the entire sky revolves around the planet.

A complete revolution of the Earth on its axis, taking the stars as a reference, lasts 23 hours and 56 minutes and 4 seconds and is called a sidereal day.

Suppose that today we align a star and note the time. Tomorrow the star will reach the same alignment 3 min 56 minutes 4 seconds earlier.

The 3 minutes and 56 seconds of difference are due to the fact that, in that time, the Earth has advanced in its orbit and has to rotate a little less to reach the same position with respect to the star.

Earth translation
Earth revolution.  Credit: web “byjus.com”

For practical purposes, in everyday life, the solar day is used, which is the time the Sun takes to reach the same point in the sky twice in a row, according to an annual average. It lasts 24 hours, or what is the same, 86,400 seconds.

Every 24 hours (every 23 h 56 minutes 4 seconds), the Earth makes a complete revolution around an ideal axis that passes through the poles.

At the equinoxes, the Earth’s axis of rotation is perpendicular to the Sun’s rays, which fall vertically on the equator.