The Sun

and other Stars

The Sun

Our Sun is a 4.5 billion-year-old star – a hot glowing ball of hydrogen and helium at the center of our solar system. The Sun is about 93 million miles (150 million kilometers) from Earth, and without its energy, life as we know it could not exist here on our home planet.

The Sun is the largest object in our solar system. The Sun’s volume would need 1.3 million Earths to fill it. Its gravity holds the solar system together, keeping everything from the biggest planets to the smallest bits of debris in orbit around it.

This illustration shows the different parts of the Sun, from the hot core where the energy is generated through regions where energy is transported outward, first by radiation, then by convection, and then out through the solar atmosphere. The parts of the atmosphere are also labeled the photosphere, chromosphere, and corona. Some typical features in the atmosphere are shown, such as coronal holes and prominences. (credit: modification of work by NASA/Goddard)

You may watch this video for more interesting facts and information about our Sun.

Layers of the Sun

The Sun’s core is extremely dense and is the source of all of its energy. Inside the core, nuclear energy is being released. Its temperature is approximately 15 million K, making it the hottest part of the Sun.

The radiative zone is the layer that lies just outside the core, to which radiant energy is transferred from the core in the form of photons. In this layer, photons bounce off other particles, following fairly random paths until they enter the convection zone.

The convective zone is the outermost layer of the solar interior. It is a thick layer approximately 200,000 kilometers deep that transports energy from the edge of the radiative zone to the surface through giant convection cells

The photosphere is the deepest layer of the Sun that we can observe directly. It reaches from the surface visible at the center of the solar disk to about 250 miles (400 km) above that. The temperature in the photosphere varies between about 6500 K at the bottom and 4000 K at the top (11,000 and 6700 degrees F, 6200 and 3700 degrees C). Most of the photosphere is covered by granulation

The chromosphere is a layer in the Sun between about 250 miles (400 km) and 1300 miles (2100 km) above the solar surface (the photosphere). The temperature in the chromosphere varies between about 4000 K at the bottom and 8000 K at the top (6700 and 14,000 degrees F, 3700 and 7700 degrees C), so in this layer it actually gets hotter if you go further away from the Sun, unlike in the lower layers, where it gets hotter if you go closer to the center of the Sun

The corona is the outermost layer of the Sun, starting at about 1300 miles (2100 km) above the solar surface (the photosphere). The temperature in the corona is 500,000 K (900,000 degrees F, 500,000 degrees C) or more, up to a few million K. The corona cannot be seen with the naked eye except during a total solar eclipse, or with the use of a coronagraph.

8 Need-to-Know Things About the Sun

BIGGEST

The Sun is about 100 times wider than Earth and about 10 times wider than Jupiter, the biggest planet. If the Sun were as tall as a typical front door, Earth would be about the size of a nickel.

STAR ATTRACTION

The Sun is the only star in our solar system. It is the center of our solar system, and its gravity holds the solar system together. Everything in our solar system revolves around it – the planets, asteroids, comets, and tiny bits of space debris.

SUN DAY

Measuring a “day” on the Sun is complicated because of the way it rotates. It doesn't spin as a single, solid ball. This is because the Sun’s surface isn't solid like Earth's. Instead, the Sun is made of super-hot, electrically charged gas called plasma. This plasma rotates at different speeds on different parts of the Sun. At its equator, the Sun completes one rotation in 25 Earth days. At its poles, the Sun rotates once on its axis every 36 Earth days.

WALKING ON SUNSHINE

The part of the Sun we see from Earth – the part we call the surface – is the photosphere. The Sun doesn’t actually have a solid surface because it’s a ball of plasma.

DYNAMIC ATMOSPHERE

Above the Sun’s surface are its thin chromosphere and the huge corona (crown). This is where we see features such as solar prominences, flares, and coronal mass ejections. The latter two are giant explosions of energy and particles that can reach Earth.

MOONLESS

The Sun doesn’t have moons, but it’s orbited by eight planets, at least five dwarf planets, tens of thousands of asteroids, and perhaps three trillion comets and icy bodies.

STARGAZERS

Several spacecraft are currently investigating the Sun including Parker Solar Probe, STEREO, Solar Orbiter, SOHO, Solar Dynamics Observatory, Hinode, IRIS, and Wind.

HOT PROPERTY

The temperature in the Sun's core is about 27 million degrees Fahrenheit (15 million degrees Celsius) – hot enough to sustain nuclear fusion. This creates outward pressure that supports the star's gigantic mass, keeping it from collapsing.

Nuclear Fusion in the Sun

The energy from the Sun - both heat and light energy - originates from a nuclear fusion process that is occurring inside the core of the Sun. The specific type of fusion that occurs inside of the Sun is known as proton-proton fusion.

Inside the Sun, this process begins with protons (which is simply a lone hydrogen nucleus) and through a series of steps, these protons fuse together and are turned into helium. This fusion process occurs inside the core of the Sun, and the transformation results in a release of energy that keeps the sun hot.

The resulting energy is radiated out from the core of the Sun and moves across the solar system. It is important to note that the core is the only part of the Sun that produces any significant amount of heat through fusion (it contributes about 99%).The rest of the Sun is heated by energy transferred outward from the core.

SEE THE SUN FROM OTHER STARS

We journey to distant suns to look back at our solar system and see its place among the stars.

Every star we see in our night sky also has a view of the Sun in its sky. Something like 9,100 stars are visible with the naked eye across the entire planet. Each appears in a particular constellation and shines with a specific magnitude, unless it's a variable star like Algol, in which case its brightness varies.

What is a Star?

a huge ball of burning and exploding gases which gives off heat and light
it burns for a million of years

Depending on that star's distance from us the Sun may appear bright or faint. From the neighboring star system Alpha Centauri, 4.4 light-years distant, it shines at magnitude +0.5, nearly as bright as Procyon in Canis Minor. But from far-flung Deneb at about 2,600 light-years you'd need dark skies and an 8-inch telescope to spot the 14.3-magnitude speck.