The Sun. Motion and constellations

Chemical composition of the Sun

The Sun is composed mainly of hydrogen (about 74% of its mass) and helium (about 24%), along with traces of heavier elements. At its core, temperatures reach 15 million degrees Celsius and pressures are enormous, allowing nuclear fusion reactions to occur in which hydrogen nuclei combine to form helium, releasing large amounts of energy in the process.

This energy is transported to the surface of the sun through a process known as convection and is then emitted into space in the form of light and electromagnetic radiation at all wavelengths, from gamma rays and X-rays to visible light and even radio waves.

Solar radiation

Solar radiation is essential for life on Earth. It is responsible for photosynthesis in plants, which converts sunlight into chemical energy and provides oxygen to the atmosphere. It is also the main source of heat on our planet, affecting weather patterns and regulating the water cycle.

Studying the Sun is fundamental to understanding how it works and predicting its behavior. Scientists use space and ground-based observatories to study its solar activity, such as sunspots, solar flares and coronal mass ejections, which can affect communications, power grids and navigation systems on Earth.

The Sun’s daily movement. The apparent movement of the Sun from Earth’s perspective

The Sun’s daily movement is the change in the Sun’s position in the sky due to the Earth’s rotation. When we look up at the sky, it appears as though the Sun is a sphere in constant motion around our planet. However, modern astronomy shows that this movement is purely an illusion. What we experience on a daily basis is not the actual journey of our star, but the optical reflection of the Earth’s own movements in outer space.

The daily path from east to west and the Earth’s rotation

The most obvious apparent motion is that which the Sun performs every twenty-four hours, rising in the east, reaching its highest point at noon, and setting in the west. This daily cycle is the direct consequence of the Earth’s rotational movement, in which our planet spins on its own imaginary axis in the opposite direction, that is, from west to east. Since we are situated on the rotating Earth’s surface, we perceive the sky as spinning around us. This continuous rotation determines the regular succession of day and night, setting the rhythm of life and enabling the functioning of traditional sundials.

The Sun’s annual journey along the ecliptic and through the zodiac constellations

In addition to its daily movement, the Sun’s position in the sky varies subtly from day to day throughout the year. If we were to record the Sun’s position at the same time each day for 365 days, we would see that it traces an imaginary line in the sky known as the solar ecliptic. The solar ecliptic is the apparent path the Sun follows in the sky throughout the year as seen from Earth. This path is the result of Earth’s orbit around the Sun and manifests as an imaginary line on the celestial sphere that traces the Sun’s position against the constellations of the zodiac. The ecliptic is tilted about 23.5 degrees relative to the celestial equator.

This annual path is due to the Earth’s translational motion around the Sun combined with the tilt of the Earth’s axis. As the Earth moves along its orbit, the Sun appears to project against different backgrounds of fixed stars in the celestial sphere. The twelve historical constellations that lie exactly along this path of the ecliptic make up the astronomical zodiac, and serve to mark the passing of the seasons and our planet’s annual journey.

The Sun’s actual movement in outer space

Although the Sun is the gravitational center of our planetary system and appears to us as a static reference point in space, the reality is that the star is not stationary. The Sun undergoes highly complex physical movements, both internally as it rotates on its own axis and on a large scale, traveling at breakneck speeds through the cosmos.

The Sun’s internal rotation on its own axis

Like the planets, the Sun rotates on its own axis, but with a unique peculiarity: since it is not a solid body but a sphere of gaseous plasma, it does not rotate uniformly. This phenomenon is known as differential rotation. The solar equator rotates much faster than the poles, taking approximately 25 Earth days to complete a full rotation at its center, while in the polar regions the rotation slows to about 35 days. This difference in rotational speed causes the lines of the Sun’s powerful magnetic field to stretch, twist, and become entangled over time, giving rise to visible solar activity such as sunspots and coronal mass ejections.

The Solar System’s orbit around the galactic center

On a macroscopic scale, the Sun participates in the Milky Way’s grand cosmic dance. Our star, dragging the Earth and the rest of the Solar System’s planets along with it, continuously orbits around the center of the galaxy. We travel at an impressive speed of approximately 220 kilometers per second. Due to the enormous size of the Milky Way, it takes the Sun between 225 and 250 million Earth years to complete a single orbit around the galactic center—a colossal period of time known in astronomy as a cosmic year or galactic year. Since its formation, the Sun has completed only about twenty orbits of the galaxy.