The Sun

As the heart of our solar system, the Sun not only holds the planets in their orbits but provides the energy that makes life possible on Earth and possibly in other parts of the solar system.

Our sun is huge with a distance of 695,000 km from center to surface and the ability to contain 1.3 million Earths. However, compared to other stars, our Sun is average, currently a yellow dwarf.

The Sun is a giant ball of gas and plasma with the vast majority of the gas being hydrogen. The blinding light and sometimes unbearable heat you experience on a summer day is the result of nuclear fusion within the core of the Sun, where energy is created from atoms combining to form heavier atoms and elements. An example of this is two hydrogen atoms combining under pressure to form helium. The extreme environment in the core of the Sun fuses 500 million metric tons of hydrogen each second!

Massive and Mighty

The Sun Stats

  • Equator circumference: 4,379,000km 

  • Radius: 695,700km

  • Temperature: 5,973°C to 15,000,000°C

  • Average orbital speed around the Milky Way: 720,000km/h (200km/s)

  • Star type: Yellow dwarf

  • Average time taken to rotate on axis: 27 Earth days

  • Number of planets: 8

Lifegiver

As evidenced by the existence of Earth and all of the organisms on it, the Sun has life-giving abilities. The solar energy created from nuclear fusion keeps the Earth at the right temperature to sustain life. In fact, there is a place called the Goldilocks Zone within all solar systems, which is the range of distance from the central star with the right temperatures for water to remain liquid. Liquid water is essential to life and a significant indicator of biological life on planets. The solar energy from the Sun not only heats up the Earth but allows plants to use the energy in photosynthesis to grow and provide food and oxygen to animals such as humans. The solar energy provided by the Sun is the first step on the path to sustainable life.

Lifetaker

The ultimate fate of the planet Earth will be when it is absorbed by our Sun in 7.5 billion years (don’t worry, you won’t be alive). All stars go through a cycle and take different forms. Our Sun will eventually exhaust the hydrogen fuel contained in its core and start only burning helium. This will force it to transition into a red giant star, expanding its girth and destroying the Earth and any life inhabiting it in the process.

Solar Activity

There is a lot of strange activity that happens on the Sun that we can observe from Earth. For example, when we look at the Sun through a telescope (with a solar lense of course), we can see dark spots. These sunspots, which are cooler parts of the Sun’s surface, are thought to be created from interactions with strong regions of the Sun’s magnetic field, reducing the radiation (light) coming from the core and cooling the surface.

Another, more dangerous event is a solar flare. Solar flares are large explosions that occur when the magnetic fields that create sunspots convert energy into heat and accelerating particles, which is ejected into space. Solar flares are the largest explosive events in the entire solar system. The Earth’s magnetic field does a good job at deflecting these accelerating particles, but a coronal mass ejection, which is a large expulsion of plasma and magnetic field from the Sun’s corona, can have some harmful effects. If one of these ejections was to arrive at Earth, it would likely produce a geomagnetic storm that could disrupt radio transmissions or destroy sensitive instruments on satellites, rendering them useless.

Here’s a video of a solar flare caught by NASA:

What is it made of?

You can think of the Sun as a continuous explosion that is being held together by the forces of gravity. Although the environment on the Sun is chaotic, creating a soup of charged particles that are endlessly interacting, the Sun still has a structure to it.

The Sun’s core is made of gas that is ten times denser than lead and has a temperature of about 27 million degrees Fahrenheit. The unusually high temperature and density allows nuclear fusion to occur naturally, creating extremely large amounts of energy, some of which will reach Earth’s surface to sustain life. The Radiative Zone is outside the core and is where photons of light (the particles of light) carry the energy from the core toward the surface as thermal radiation (heat), which can take millions of years. The temperature here gets as low as 4 million degrees Fahrenheit and this zone extends about two-thirds of the way to the surface. The outermost region of the Sun’s interior is the Convective Zone. It is called so because of the convection currents present. Hot plasma, which is just superheated, charged gas, carries the energy that came from the depths of the Sun to the surface. In doing so, it cools as it moves to the top of the zone to about 10,000 degrees Fahrenheit. Since “cold air sinks," the hot plasma becomes denser and sinks toward the bottom of the convective zone before being heated and repeating the process again. You can think of this plasma as a transporter, like a bus driver going back to the station to pick up passengers (the energy) and drop them off at the next station (the top of the convective zone).

The Core, The Radiative Zone, and The Convective Zone make up the interior layer of the Sun. The first part of the outer layers is the photosphere, which is visible to us. This layer is where granules of plasma and sunspots can be seen, and it is also the source of solar flares. The temperature here is from 7,500 to 11,000 degrees Fahrenheit. Since photo means "light,” think of this layer as the visible one that allows us to view the Sun with the naked eye. The next outer layer is the chromosphere. This layer emits a reddish glow from as hydrogen burns off but is too weak to be seen against the brighter photosphere. It is thought that the chromosphere plays a role in conducting heat from the interior of the Sun to the corona, which is the outermost layer. The corona extends into space and appears as white streamers or plumes of ionized gas. It is actually 300 times hotter than the photosphere even though it is so far from the core, which is something that is still a mystery. Both the chromosphere and the corona cannot be seen with the naked eye unless you are viewing the Sun during a total solar eclipse. In this case, while the Moon covers the Sun, the red chromosphere and white corona can be seen and it is quite beautiful.