If we observe the sun every day at the same time after an entire year we will see how, by superimposing the photos, it makes a shape of an 8. This is known as analemma and that it is due to the inclination of the Earth's axis and the translation of the Earth in a slightly elliptical orbit.
In this article we are going to explain to you what the phenomenon known as analemma consists of, its characteristics and importance.
What is an analemma
An analemma is a term that It is used in astronomy and geography to refer to a figure in the shape of an eight (8) which is formed when the positions of the Sun in the sky are recorded at the same time of day and in the same place over the course of a year. This figure-eight pattern is due to the tilt of the Earth's axis and its elliptical orbit around the Sun.
The analemma is made up of two main components: the northern component and the southern component. The northern component is the top of the "eight" and shows the positions of the Sun during the spring and summer period in the northern hemisphere, when the Sun is highest in the sky. The southern component, on the other hand, corresponds to the autumn and winter period in the northern hemisphere, when the Sun is lowest in the sky.
This phenomenon is the result of the combination of two movements of the Earth: the tilt of its axis and its elliptical orbit around the Sun. The tilt of the Earth's axis causes the Sun to appear in different positions in the sky throughout the year, while the elliptical orbit causes the Earth to move at different speeds throughout its orbit, which also affects the apparent position of the Sun.
The analemma is a graphical representation of the equation of time, which is the difference between real solar time and mean solar time. This difference is due to the fact that the Earth's orbit is not perfectly circular, and the speed at which it moves around the Sun varies throughout the year. Therefore, the analemma is a visual way of showing how "real" solar time can vary relative to mean solar time throughout the year.
Some history
Already in the Middle Ages it was necessary to determine the time of the equinox to determine the first equinoxes, and in this year, Paolo del Pozzo Toscanelli calculated the layout of the first meridians, which not only provided the events of noon with great precision, but It is also possible to determine the time of year.
This meridian was built in the Cathedral of Santa Maria del Fiore in Florence, Italy. The meridian was built with strips of marble on the floor and a hole was cut in the south wall to allow a luminous point to pass through it to indicate the date of the year on the scale. This procedure of constructing the meridian was known as analemma.
Mechanical advances in the XNUMXth century made mechanical clocks increasingly precise, and with the advent of the pendulum clock it became possible to measure minutes with great precision. At this point the difference between solar time measured by sundials and civil time measured mechanically by conventional mechanical clocks begins to appear, which is given by the equation of time. It was probably around this date when the term analemma became confused, going from a chronological procedure to a representation in graphic space.
Pattern that follows
Because the Earth's axis is tilted at an angle of 23,4 degrees, The Sun's position in the sky appears to change as the Earth completes its rotation around the Sun. As the Earth orbits the Sun on its tilted axis, the Sun's perceived position in the sky changes up and down in a North-South direction. This results in the formation of the figure-8 pattern consisting of two loops.
During the summer, the upper part of the analemma figure occurs. As summer progresses, the Sun gradually rises higher into the sky and finally reaches its apex during the summer solstice. After the summer solstice, the Sun's perceived location begins its descent in the sky, producing the initial loop in the pattern. This phenomenon is also replicated in the winter season, resulting in the creation of the second loop in the figure-eight trajectory.
Assuming that the Earth's orbit was elliptical, but Without any axial inclination, the solar analemma would adopt an oval shape. The analemma, seen from the equator, would be a straight line running horizontally from west to east.
In the event that the Earth's orbit was circular, its axial tilt would produce a figure-8 analemma curve that is perfectly symmetrical in size for both its upper and lower loops. However, this is not an accurate representation. Earth's orbit It is elliptical and the Sun is off-center from its path. This discrepancy results in one point on the path, called Perihelion, being closer to the Sun than the other point, called Aphelion.
How the analemma is generated
The speed of the Earth's rotation around the Sun varies depending on its position in its orbital path. When the planet is at its closest point to the Sun, known as perihelion, which occurs around the winter solstice, moves at a faster pace. In contrast, when the Earth is at its furthest point from the Sun, Aphelion, it moves at a slower pace. This phenomenon results in a flattened lower half of the curve.
The analemma curve shows a different pattern between the northern and southern hemispheres. In the Northern Hemisphere, the bottom of the curve forms the widest loop, while in the Southern Hemisphere, the top of the curve forms the widest loop.
Those who observe the analemma at the North Pole will witness only the upper curvature, while those at the South Pole will only see the lower portion of the Analemma. It should be noted that the orientation of the analemma will change depending on the specific location of the observer on the Earth's surface. Each planet in our solar system has its own individual analemma.