Sun

Not to be confused with Son!

The Sun as viewed by a satellite.

The Sun is the only star in the Solar System. It is a yellow dwarf star. A yellow dwarf star is one of the coldest of them, just after the red star.

The Sun is orbited by four terrestrial planets, the asteroid belt, four gas planets, Kuiper belt, and the Oort cloud. There used to be nine recognized planets, when Pluto was still considered a planet. Since 2006, when scientists discovered several celestial bodies of similar size and mass, Pluto, along with Eris, Ceres, Makemake, and Haumea, became known as dwarf planets.

The Sun rotates on its axis in 25 days (at its equator, 35 days at the north and south poles). Its diameter is approximately 1.4 million kilometers, 109 times that of Earth's, and its mass is nearly 1.99 billion tons (or 1.99×1030 kg, which is 333,000 times the mass of the Earth): this represents 99.86% of the mass of the solar system, or nearly 1,000 times the mass of all the celestial bodies that orbit around it (including Jupiter).

On Earth and other planets in the Solar System, when the Sun rises, it is day, but when it goes down, it is night. From Earth, the Sun rises in the East and sets in the West.

The temperature on the surface of the Sun is about 5,500° Celsius, and it can go up to 15 million at its planetary core.

The Sun is expected to disappear in about 5 billion years. In fact, stars in this category (yellow dwarfs) live for 5 to 20 billion years, and scientists have calculated that the Sun is about 4.6 billion years old. The Sun has a life expectancy of about 10 billion years, so it is currently about halfway through its life. Around that time, when the Sun uses up all of its hydrogen, helium will then become its new source of fuel, causing the Sun to evolve into a red giant, two hundred times larger than it is now.

Every culture features the Sun as a very powerful symbol of power and life. Many ancient religions worshiped the Sun as one of the major gods.

Formation

The Sun was born about 4.568 billion years ago in a second-generation nebula, known as a solar nebula. When gas and dust were sucked into a part of the nebula, this dense part of debris began to rotate, gravity caused it to shrink to form a huge disk, and formed a young star that we know as the Sun.

Energy

The sun, shining above the ocean. It appears white because of the light rays, not because the Sun is actually that color.

Hydrogen makes up nearly 74% of the Sun's mass, and helium 25%. In terms of atoms, hydrogen accounts for 92% of the Sun's atoms and helium just under 8%. Nuclear fusion reactions take place in the Sun, turning 620 million tons of hydrogen into 615.7 million tons of helium every second; this means that the Sun produces more than 4.3 million tons of energy every second, but this is very little compared to its immense mass (roughly the mass of Earth lost in 50 million years). The nuclear fusions release a lot of energy, which is how the Sun shines very brightly.

The amount of energy radiated by the Sun is enormous: In a single second, it produces 1 million times more than all of humanity produces in one year. The Earth receives about 1 billionth of this energy. The energy reaches the Earth in the form of heat and light radiation (light rays).

Most living things on Earth get their energy from solar energy produced by the Sun, either directly or indirectly. Plants can turn the Sun's energy into chemical energy through a process known as photosynthesis; this chemical energy is then used to make sugars and then all the molecules in plants and green algae. Herbivores and omnivores then eat these plants and derive their energy from them through solar energy indirectly.

The Sun usually appears as a very bright white circle of light in Earth's sky. That does not mean the Sun is actually white, but rather appears this way from a combination of several rays of different colors. The brightness of the Sun can be dangerous because of someone stares at it for too long, even through sunglasses, they can become blind. The sun is often blocked by clouds, but its rays are still bright enough to ensure that it is not dark during the day.

However, it appears red during sunset. When the Sun is directly overhead (at its zenith), its light must pass through the atmosphere, which has a certain thickness, but during sunset or sunrise, the light passes through the atmosphere at an angle, meaning that it travels a greater distance. The atmosphere may look transparent, but this is because it does not allow light to pass through as easily as that. When a thin layer of atmosphere is crossed by sunlight (when the Sun is high in the sky, for example), all the rays manage to pass through, but when this layer becomes thicker, not every ray manages to pass through. Blue and violet rays are more easily deflected from their path by the atmosphere, and only red rays pass through without too much difficulty.

Solar panels capture solar energy and transform it into electricity, a type of renewable energy. The principle of the photovoltaic solar panel was described by Albert Einstein, which earned him the Nobel Prize in Physics.

Distance

Comparative sizes of the Sun, planets (top), and dwarf planets (bottom). Earth is the third planet to the right of the Sun. Distances are not to scale; a much larger image would have been required for that.

The Sun is 150,000,000 kilometers from Earth. It takes the Sun's energy and light approximately 8 minutes and 19 seconds to travel, at the speed of light, the distance between it and Earth; therefore, it would take 154 days by rocket to reach the Sun at a continuous speed of 10 km per second.

The Earth's orbit can vary between an almost perfect circle and an ellipse in its path around the Sun. It is closer or further away from the Sun during the different seasons.

There is a unit of length known as the astronomical unit (AU), which covers the relative length between the Sun and Earth.

Structure

Structure of the Sun in section.

The Sun is made up of 6 different layers, like other yellow dwarves.

1. The core (15 million °C) and where nuclear fusion reactions occur.
2. The radiative zone, which generates energy from the core outward.
3. The convection zone, circles of heat that bring energy to the surface
4. The photosphere, the surface of the Sun, with a temperature of about 5,500°C.
5. The chromosphere, the lower atmosphere of the Sun.
6. The stellar corona, the upper atmosphere of the Sun, with a temperature ranging from 1 to 2 million °C.

All solar energy is generated in the Sun's core, which is about a quarter of the Sun's diameter. The area beyond the core is the radiative zone, which is so dense that radiation cannot simply leave the Sun; it constantly collides with plasma particles before being absorbed and released in other directions. The convective zone is made up of regions where plasma rises. The energy produced by the core takes 10 days to pass through the convective zone. The energy then passes through the photosphere, the surface of the Sun, then the chromosphere (the Sun's lower atmosphere) and finally the solar corona.

Rain on the Sun

The Sun also has an atmosphere. It sometimes produces huge arcs of fire, known as solar prominences, that spread out into space. They are composed of a liquid called plasma, which creates magnetic field lines in space that fall back onto the Sun in a phenomenon also known as coronal rain.

Cycle

The solar surface follows an 11-year cycle. According to scientists, the Sun begins this cycle with the formation of a new magnetic field between the convective zone and the radiative zone. Below this zone, the deeper inner part of the Sun rotates at a constant speed. The convective zone rotates faster at the equator, so it rotates unevenly. This uneven movement gradually distorts the magnetic field between the convective zone and the radiative zone, pushing its lines out of the Sun, which form colder, but still extremely hot, areas called sunspots.

Later, the magnetic field becomes more distorted and more and more of its lines appear on the surface. Over time, the sunspots move closer to the equator and neutralize each other until there are no sunspots or magnetic field left on the Sun. A new magnetic field then forms, but it is oriented in the opposite direction to the previous magnetic field, and a new 11-year cycle begins.

In mythology

Many years before the age of science, people worshiped the Sun. It was considered a source of life. It was sometimes even regarded as a god and offerings were made to it. The Mayans, Aztecs, Toltecs, and Incas built temples aligned with the sunrise and sunset. The Aztecs in particular considered the Sun to be a powerful god, and many human sacrifices were made during solar eclipses. In Greek mythology, the Sun is driven by the chariot of the god Helios.

The famous Stonehenge site in England is believed to be one of the oldest monuments, having been built between 3,000 and 2,000 BC. It could have been dedicated to the Sun, since the alignment of certain stones correspond exactly to the location of the setting and rising of the Sun. It is possible that the Stonehenge was used as a calendar, but nobody knows what purpose it had or why it was built.

In popular culture

A lot of fictional media depicts a Sun with a human face.

Video games

• Mario franchise: One of the enemies is the Angry Sun, which debuted in Super Mario Bros. 3 and has rarely made reappearances.

Television shows

• Teletubbies: There is a character known as the Baby Sun, which is a Sun with a baby's face.

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Source : This page has been adapted from the page « Soleil » on Vikidia in French. (Authors list)