Sun

We explain everything about the Sun, its origin, composition and what its structure is like. Also, what are its characteristics and its importance for life on our planet.

What is the Sun?

The Sun is a star located in the center of the solar system, and is the primary source of light and energy for Earth. All the planets of the solar system orbit around it, attracted by its gravity, as well as the comets and asteroids that accompany them. It is located an average of 149.6 million kilometers from Earth.

It is a G2-type yellow dwarf star, which means that, relative to other stars, it has a moderate temperature and is in its main sequence of evolution. It is located in the outer region of the Milky Way, in one of its spiral arms, 26,000 light years from the center of the galaxy.

The size of the Sun is so large that it represents more than 99% of the mass of the solar system, which is equivalent to 743 times the total mass of all the planets combined. It has a diameter of 1,400,000 kilometers, and thanks to its constant emission of electromagnetic radiation, the Earth receives heat and light, which makes the development of life possible.

Characteristics of the Sun

The main characteristics of the Sun are:

• It is located in the center of the solar system.
• It is the main source of heat and energy for the Earth.
• It is located 149.6 million kilometers from Earth on average.
• It has a diameter of 1,400,000 kilometers.
• It is classified as a G2 type dwarf star.
• It was formed 4.6 billion years ago.

Origin of the Sun

The Sun originated, like all stars, from gas and other materials that were part of a large molecular cloudfrom which the entire solar system comes. That cloud collapsed under its own gravitational forces 4.6 billion years ago, and as a result of the collapse, it contracted to form a rotating disk around a central core. This gaseous mass became so dense that it gave rise to nuclear reactions that “ignited” the core of the star, and in this way the Sun was formed. This is the most common process of formation of these celestial bodies.

Composition of the Sun

The Sun is mostly composed of hydrogen and helium, the two most abundant elements in the universe.. These gases represent more than 99% of the Sun’s total mass. The approximate proportion is 74% hydrogen and 24% helium. To a much lesser extent, the Sun is also composed of oxygen, carbon and nitrogen.

Nuclear fusion takes place at the heart of the Sun, in which hydrogen atoms are transformed into helium atoms through a series of reactions. These reactions release enormous amounts of energy that fuel the Sun’s luminosity. In this way, hydrogen acts as the fuel that produces the Sun’s light and heat.

This energy in the form of electromagnetic radiation radiates from the Sun and is essential to provide the light and heat that reaches the Earth.

Structure and size of the Sun

The Sun has an approximate diameter of 1,400,000 kilometers, and a mass that represents 99.86% of the total solar system.. Its gravity is strong enough to keep planets and other objects in orbit around it.

The Sun is structured in the following layers:

• Core. It is the innermost region of the Sun. It occupies one fifth of the star, about 139,000 kilometers of its total radius. It is where the conversion of hydrogen into helium happens.
• Radiant zone. It is the area in which energy-carrying particles try to escape towards the outside of the Sun.
• Convective zone. It is the area in which the columns of hot gas rise and when they approach the surface they descend again.
• Photosphere. It is the area where visible light from the Sun is emitted. Sunspots also appear there, which occur in areas where the Sun’s temperature is higher.
• Chromosphere. It is the outer layer of the photosphere, much more translucent and difficult to see. During a total solar eclipse, the chromosphere becomes visible as a deep red ring around the dark edge of the Moon.
• Solar crown. It is the thinnest layer of the external solar atmosphere, in which the temperature increases considerably compared to the other layers.

Solar light and wind

Sunlight is made up of 50% infrared light, 40% visible spectrum and 10% ultraviolet light. On Earth, some of the solar radiation is absorbed by atmospheric components such as ozone, water vapor and carbon dioxide. Some particles and clouds reflect and scatter solar radiation back into space. In this way, radiation that is neither absorbed nor reflected is transmitted to the Earth’s surface in the form of light and heat.

Solar radiation also heats the atmosphere, producing weather events and climate patterns critical to our planet’s atmospheric dynamics.

The solar wind is a constant flow of charged particles that break off from the Sun’s outer atmosphere and propagate throughout the solar system.. It is composed mainly of protons and electrons. The solar wind is a direct result of the high temperature and energy in the solar corona, where particles gain enough thermal energy to overcome gravity and escape into space.

Solar flares

Solar flares are characterized by the sudden and violent release of energy into the Sun’s atmosphere.. These events include the ejection of solar material, the emission of electromagnetic radiation and the release of charged particles.

The frequency of solar flares varies depending on the solar cycle, which is a period of approximately eleven years during which solar activity experiences peaks and dips. During solar maximum, solar flares are more frequent, and during solar minimum, they occur less often.

The energy released during a solar flare spreads mainly into space and does not reach the Earth’s atmosphere in sufficient quantities, so it does not have the power to affect the Earth’s climate.

Importance of the Sun

The Sun plays an essential role for the sustainability of life on Earth:

• main source of energy. The Sun acts as the main source of energy for the Earth. Through nuclear fusion, it releases a huge amount of energy in the form of electromagnetic radiation, including visible light. This solar radiation is essential to fuel biological and chemical processes on our planet.
• Light and heat. The Sun provides lighting and heat to the Earth. Sunlight enables photosynthesis, a process by which plants convert solar energy into stored chemical energy and release oxygen. Solar heat, by heating the Earth’s surface, influences weather patterns, ocean currents and other atmospheric processes.
• Climatic influence. Solar radiation drives Earth’s climate system. The unequal distribution of this radiation in different regions and seasons of the year contributes to the formation of the different climates on the planet.
• Sustaining the food chain. Solar energy captured through photosynthesis forms the base of the food chain. Plants, by using this energy to produce their own food, serve as a source of nutrition for herbivores, and so on. This flow of solar energy through the food chain sustains life on Earth.
• Regulation of the water cycle. Solar radiation drives the water cycle, which includes evaporation, cloud formation and precipitation. This cycle is essential for the distribution of water on Earth, determining the availability of water resources and the regulation of ecosystems.

Observation and exploration of the Sun

Observation of the Sun dates back to ancient civilizations, and was steeped in mythological and cultural meanings. Although they lacked the technology of modernity, ancient cultures recorded and attempted to understand the movement of the Sun in the sky. Many of these societies developed calendars based on the observation of the Sun, since its cycle marked events such as the seasons and the beginning of agricultural periods.

Systematic monitoring of solar variations began with the invention of the telescope at the beginning of the 17th century. Galileo Galilei, in 1610, observed sunspots and revealed that the solar surface was not uniform.

The development of photography in the mid-19th century allowed for the systematic documentation of solar activity, and the 20th century marked the beginning of space exploration of the Sun. Thus, the Solar and Heliospheric Observatory (SOHO) probe, launched in 1995, provided Detailed images and precise measurements of solar activity.

More recent missions, such as the Solar Dynamics Observatory (2010) and the Parker Solar Probe (2018), remain in orbit and provide data on solar physics and its impact on the space environment.

When will the Sun go out?

The Sun lives in its intermediate age and has not changed much for almost 4 billion years. However, it is known that at some point it will go out.

In about 5 billion years, the Sun will run out of hydrogen in its core.. As a result, the core will contract, while the outer layers will expand, turning the Sun into a red giant. During this phase, it is believed that the Sun will absorb the nearest planets, including Earth.

Additionally, in the red giant phase, the Sun will lose its outer layers in the form of solar wind and mass ejections. The remaining core will shrink and become a white dwarf.

The white dwarf will be the final stage of the Sun. It is a dense and hot object that will cool over billions of years. Eventually, it will become a black dwarf, a celestial object that will gradually cool until it goes out.

References

• AstroMía. (sf). Structure and composition of the Sun. https://www.astromia.com/
• Bachelor, R. (sf). The Sun: our star, our energy. National Astronomical Observatory, National Geographic Institute, Ministry of Public Works. https://astronomia.ign.es/
• Doddoli, C. (2021). The Sun, the closest star to Earth. National Autonomous University of Mexico, General Directorate of Science Dissemination. https://ciencia.unam.mx/
• National Geographic. (sf). white dwarfs. https://www.nationalgeographic.es/