Introducing the Sun
Solar corona (dem10, Getty Images)
Solar corona (dem10, Getty Images)
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Learn the basics of the star we call the Sun.
Can you see stars during the day? Yes, you can! Our Sun is a star! From morning until evening you can see the Sun in the sky. The Sun is one of 200 billion trillion stars in the universe. The Sun is the closest star to Earth. In fact, our entire solar system revolves around the Sun.
What is the Sun?
To find out what the Sun is, first we must find out what a star is! Stars are formed from clouds of gases and dust. These clouds are scattered throughout most galaxies. Sometimes materials in the clouds clump together. This begins to create gravity that pulls in even more materials. The force of the gravity causes the materials to heat up. Eventually the centre, or core, gets hot enough for nuclear fusion to take place. At this point, a star is born.
What is the Sun made of?
The Sun isn't solid and rocky like Earth. Instead, it is a massive glowing sphere of hot gases. It's mostly made of the chemical elements hydrogen and helium. A small percentage of the Sun is made of carbon, nitrogen and oxygen. There are also small amounts of iron, nickel and other elements.
Image - Text Version
Shown is a colour diagram of the sun as a pie chart showing 72% Hydrogen, 26% Helium and 2% Other. The title “Composition of the Sun” is in white letters across the top of a dark blue background. Below, on the left, the Sun is represented as a circle with a border of pointed yellow rays. The middle of the sun is a pie chart. The largest section is light orange, a smaller section is darker orange, and the smallest is red. On the right, a square of each colour is labelled. Pale orange - “72% Hydrogen”, dark orange - “26% Helium” and red “2% Other.”
Parts of the Sun
The Sun is made of many different layers. These layers can be broken down into two sections:
- Inner Layers
- Outer Layers
Image - Text Version
Shown is a colour photograph of the Sun, sliced to reveal the layers inside. On the left side of the sphere, a photograph shows the visible layers on the outside of the Sun. The right side is divided into two quarters. The top quarter illustrates each inner layer with a different colour. The bottom quarter shows photographic renderings of the outer layers. A blue line leads from each layer to a label to the right of the Sun. The title above this list reads “Layers of the Sun.” Starting at the top of the list, the first label reads “Core, Temperature: 15 million K.” A line points from here to the innermost part of the sun, shown as a white circle. The second label reads “Radiative Zone, Temperature, 7 million K.” A line points to a thick yellow ring around the core. The third label reads “Convective Zone, Temperature: 2 million K.” This line points to an even thicker red ring outside the radiative zone. The next layer is shown below, as orange, with a few lumps of darker material. This is labelled “Photosphere, 4 000 - 6 500 K.” Here, the list is divided by a white line. An arrow labelled “Hotter” points up from the line. Another arrow , below the line, points down. This is also labelled “Hotter.” The next label reads “Chromosphere, Temperature: 4 000 - 8 500 K.” A line points from here to the left side of the sphere. This layer is orange with a texture of darker orange and red lumps throughout. Bright white light shines through the layer in a few places. The last label reads “Corona, Temperature: 500 000 K - 1 million K.” A line points to the area that appears outside the main sphere of the Sun. It looks like wispy orange strands of light rising from the surface of the corona.
Inner Layers
Core
This is the hottest and densest part of the Sun. In this region, hydrogen transforms into helium through nuclear fusion. This process generates bundles of light energy we call photons.
Radiative Zone
This region is less dense than the core. Here energy moves from the core outwards.
Convection Zone
In this region, energy moves from the inner layer to the outer layer.
Outer Layers
The outer layers make up the Sun's atmosphere. Energy radiates into space from these regions.
Photosphere
This is the part that we refer to as the surface of the Sun. This layer is the source of all solar energy that reaches the Earth. The name of this region comes from ancient Greek words “photos” meaning light and “sphaira” meaning sphere.
Chromosphere
The name of this region comes from ancient Greek words “chromo” meaning colour and “sphaira” meaning sphere. This layer looks reddish because it gives off a type of electromagnetic radiation in the red part of the spectrum. Solar prominences and solar filaments are formed in this region.
Image - Text Version
Shown is a colour photograph of the outer layers of the Sun, with a wispy loop-like feature extending into space. The Earth is tiny in the background. The curved surface of the Sun fills the lower right half of the image. It appears mottled in orange and red. It has an uneven edge of orange streaks against black space. A loop of dark orange streaks extends out from a brighter orange part of the surface. Above and behind this, the Earth is shown as a tiny blue sphere against black space. This is labelled “Approx. size of Earth.”
Corona
This is the Sun's outermost layer. This layer usually is outshone by the other layers of the Sun. However, the corona can be viewed during a total solar eclipse. The corona is the hottest part of the outer layers. Why is this layer so hot? The NASA Parker Probe was sent to the Sun to find out.
NASA's Parker Solar Probe Touches The Sun For The First Time (2022, 5:14 min.)
How old is the Sun?
A star’s life cycle is closely connected to its size. Small red dwarf stars have fusion that takes place very slowly. These stars can exist for trillions of years. Eventually, they collapse to form white dwarfs. Over time, these cool to form black dwarfs.
Mid-sized stars, like our Sun, begin to change as they use up their hydrogen. They contract and heat up, becoming red giants. As red giants cool, they give off layers of glowing gas we call planetary nebulas. They too eventually become white dwarfs.
For the largest stars, their life cycles end with a dazzling explosion known as a supernova. These events release huge amounts of energy, and trigger the formation of heavier chemical elements, like gold. After a supernova, the core can become either a neutron star or a stellar black hole.
Neutron stars are the smallest and most dense types of stars. The average radius of a neutron star is only 10 kilometres! A stellar black hole has gravity that is so strong that even light cannot escape. Scientists usually detect black holes by noticing how gases from nearby stars are pulled into them.
Our Sun is approximately 4.5 billion years old, which makes it a fairly young star. The Universe itself is estimated to be at least 13.7 billion years old. But scientists at the University of Ottawa think that the Universe might be as much as 26.7 billion years old. Most stars have a lifespan of about nine or 10 billion years, making our Sun a middle-aged star.
Did you know?
The oldest star known is called Earendel. It is a star in the constellation of Cetus. It is estimated to have been formed around 900 million years after the Big Bang.
How big is the Sun?
The Sun is part of a group of stars we call G-type main-sequence stars, or yellow dwarfs. The stars in this group come in a wide range of sizes and luminosity (brightness). They range from one-tenth to 200 times the Sun's mass.
The Sun has a diameter of 1.4 million kilometres (865,000 miles). Its diameter is about 109 times the diameter of the Earth. It would take more than one million Earths to fill the Sun’s entire volume.
Image - Text Version
Shown is a graph with colour illustrations of stars plotted at their temperature and luminosity. The graph is on a black background with white text and brightly coloured circles. The X axis is labelled “Temperature (Kelvin).” This runs from 40 000 on the left to 3 000 on the right. The Y axis is labelled “Luminosity (Sun = 1).” This runs from 0.0001 at the bottom to 10 000 at the top. Starting at the bottom, the first group of stars are small white circles in a streak. Their temperature goes from about 6 500 K to over 20 000 K. Their luminosity goes from about 0.01 to 1 Sun. Above, a long streak of circles runs diagonally from 3 000 to 30 000 K and 0.0001 to 10 000 Suns. This is labelled “Main Sequence.” The circles start small and red, then slightly larger and orange, slightly larger and yellow, then white and pale blue. At the end of the streak are large circles in light, medium and dark blues. One of the yellow, medium-sized circles is labelled “Sun.” One of the large, light blue ones is labelled “Riegel.” Above the main sequence, three large, pale blue circles are labelled “Supergiants.” These are between 7 000 and 20 000 K and sit above and below the 10 000 Sun mark. Below and to the right of the supergiants are two medium yellow circles. One is labelled “Pole star.” They are between 6 and 7 00 K and around the 100 Sun mark. Above and to the right are three medium and one large orange circles. These are labelled “Arcturus.” These are between 4 000 and 6 000 K and 100 to 10 000 Suns. Both Pole Star and Arcturus are labelled “Giants.” Above and to the right of the giants are two red circles. The lower one is labelled “Antares” and the upper one “Betelgeuse.” These sit just over the 3 000 K mark and just above and below the 10 000 Sun mark.
Where is the Sun located?
The Sun is found in the Orion Spur of the Milky Way Galaxy. The spur juts off the Sagittarius arm, which is one of the spirals that make up the galaxy.
The Sun follows a clockwise orbit around the centre of the galaxy, which is between 24 000 and 26 000 light years away. This orbit takes roughly 225 to 250 million years to complete.
Image - Text Version
Shown is a colour illustration of the Milky Way overlaid with a circle illustrating the Sun’s orbit. The galaxy is shown as a pinwheel of curved blueish white streaks dotted with pink and red, against black space. In the centre is a pale gold, diagonal streak. Around the centre of the galaxy, about halfway out, is a thin yellow circle labelled “Sun’s orbit.” At the top of this is a small red dot.
The Sun is at the centre of our Solar System. It is approximately 150 million kilometres (93 million miles) from Earth. This location, which is neither too close to, nor too far from the Sun, allows life to occur on Earth.
What does the Sun do for the Earth?
The Sun is extremely important for life on the Earth. It provides light and heat for plants and animals, including humans. The Sun’s light enables plants to store energy through photosynthesis. Humans and other animals rely on these plants for food.
Because of its distance from the Sun, Earth is able to have liquid water. If it was too far from the Sun, the water would be all frozen. If it was too close, the water would all evaporate. Water is essential for most living things on Earth.
The sun also has other important influences on our planet. It is the driving force of our weather patterns, ocean currents, seasons and climate. Without the Sun, life on Earth would not be possible as we know it.
Why do we call it the “Sun”?
The word “Sun” comes from the latin word “sol.” This word is used as the main adjective for many Sun-related terms in English, such as solar. Many cultural communities have their own word for the Sun.
The Sun has played an important role in different communities across the world over time. In ancient Greek myths, Helios is the Sun god. This name is also used in many Sun-related terms, like heliosphere and helioseismology.
Inti, also called Apu-punchau, is the Sun god from ancient Inca mythology. Ancient Mayan mythology features a Sun god called Kinich Ahau. Amaterasu Ōmikami is the celestial Sun goddess in the Shinto faith. Each of these deities has a detailed narrative, and is important in their respective culture.
Above the Arctic circle, some Inuit, Yupik, Aleut, Chukchi and Iñupiat people observe the first sunrise on the first day of the year (Inuktitut: ᓯᕗᓪᓕᖅᐹᖅ ᓯᕿᓂᖅᓄᐃᔪᖅ) by extinguishing three qulliqs (traditional oil lamps) and relighting them. This ritual celebrates the story of both Sun and her brother Moon, who are known by several different names across the circumpolar world.
Learn More
Sun 101 (2018)
This National Geographic video (5:01 min.) provides a comprehensive examination of the Sun. Delving into its various layers, composition, and the intricate processes like thermonuclear fusion, gravity, and the magnetic field, the video offers an in-depth understanding of our closest star.
Scale of earth and sun (2010)
In this Khan Academy video (9:31 min.), viewers gain a perspective on the scale of our Earth in relation to the Sun. The video extends this comparison to encompass the other planets within our solar system, providing a comprehensive understanding of their relative sizes. It also delves into the vastness of the universe by contrasting the Sun with other stars.