Category Archives: Sun

What is the radiative zone in the Sun?

What is the Radiative Zone?

A radiation zone is a layer in the interior of a star where energy is transported outwards by radiative diffusion and thermal conduction rather than by convection.

The opacity and radiation flux within a star’s layers determine how effective radiative diffusion is at transporting energy. High opacity or high luminosity causes a high-temperature gradient.

Layers of the Sun Explained – Inner Layers. The existence of all life on Earth depends on the sun. It determines time and climate and is the center of our solar system. Astronomers estimate our sun will die in a few hundred million years when all of its nuclear fuel will have burnt up, and the planet will cease to exist. Fortunately, we can attain the infinite energy of the sun early, even before it is dead. #sun

It’s official: Astronaut’s brain grows after spaceflight in outer space

Recommended post

The radiation zone is stable against the formation of convection cells if the density gradient is high enough.

A polytrope solution with n=3 and a left-hand side constant gives a stable radiation zone against convection.

At a sufficiently large radius, the opacity increases due to the decrease in temperature and possibly also due to a lower degree of ionization in the lower shells of the heavy element ions.

Main sequence stars are entirely convective below 0.3 solar masses and have a radiative zone around the stellar core. Above 1.2 solar masses, the radiative zone becomes a convection zone.

The radiation zone is a region of the Sun between the solar core and the outer convection zone.

The radiation zone is a thick layer of highly ionized, very dense gases that are constantly bombarded by the gamma rays of the nucleus. It consists of about 75% hydrogen and 24% helium. Since most of the atoms here lack electrons, they cannot absorb photons that might penetrate the surface. Most photons simply bounce back. Occasionally, a photon is absorbed.

When the Sun cools from a fusion fireball to a plasma ball, it happens at the interface between the radiation zone and the radiation zone. No convection occurs in this layer, he said. Instead, heat is transferred via thermal radiation. The incoming light particles (photons) are absorbed in specific ways by specific atoms inside the star before being transmitted back at higher frequencies. It can take light particles thousands of years to spiral through this layer before they finally reach the star’s surface.

What is the Sun’s nuclear fusion?

Because all other protons repel all other protons, the average proton must collide head-on with another proton and be fast enough to merge in 7 billion years. In the Sun, there are many protons, so some collide in seconds, and others never will. This is why the sun doesn’t explode all at once. Due to the instability of the two-proton nucleus, one of the protons decays into a neutron right away. Neutrinos and positrons are released during the decay. As the positron collides with the electron (the antimatter equivalent of the electron), both become gamma rays. After leaving the sun, neutrinos travel at nearly the speed of light.

What is the difference between a nucleus and an atomic nucleus?

These two collide, forming for a moment a sphere with four protons and two neutrons. But two protons are knocked away by the force of the collision, leaving a stable helium nucleus with two protons and two neutrons.

What is the Sun’s origin?

Five billion years ago, the Sun’s predecessor was a cloud with a diameter of 500 trillion kilometers or 50 light years. It was a near vacuum.

What Happens When a Cloud collapses?

These globules were still what Earth would consider a vacuum, and their temperatures had only risen to -400° F (-240° C). They were visible only as dark circles beneath a blanket of dust, and each orb was a trillion miles across and 25 solar masses in mass.

What was the Sun’s diameter?

After a few more thousand years, our sun had a diameter of about 225 million miles. The temperature in the core often exceeded 60 000 °C, which is hot enough to remove the electrons from the atoms, but not yet hot enough to melt two hydrogen nuclei. The surface temperature was about 1500 °C, cooler than the Sun’s surface today, but large enough to emit many times more light than the Sun.

What Happens When the Sun collapses?

After five billion years, fusion in the Sun’s core will cease and gravity will cause the star to collapse. The heat of the collapse will exceed the heat of fusion; it will even reach 150 000 000 000° F (about 80 000 000 000° C), and the Sun will expand for a few hundred million years, eventually swallowing up the planet Mercury. As the Sun grows, it will become a red giant. Then its surface will be so large that it will emit 500 times more light than it does today.

What happens when it produces too much heat?

The core will then be hot enough to melt helium into carbon and oxygen. Fusion will generate more heat, so much so that the new helium-rich nucleus can no longer radiate. In a few hours, the core will explode. The Sun’s outer layer absorbs the explosion. The core will lose enough heat to stabilize and begin to collapse. Again it will produce too much heat and explode, causing the Sun to swell dramatically. This process will repeat, so the Sun will grow and shrink many times.

What is the core of the sun made of?

The core of the Sun is made up of 64% helium, surrounded by a shell of molten hydrogen – 35% of the core’s mass. All the other elements in the Universe make up only 1% of the Sun’s core. All the energy the Sun radiates is generated in the core. The energy generated every second by 4.5 million tonnes of matter in the core raises its temperature to a spectacular 14 000 000 °C. 

The nuclear reaction that takes place in the nucleus produces tiny particles called neutrinos that react surprisingly little with matter. These particles rush out of the Sun at almost the speed of light and take just five seconds to do so. The energy produced by this reaction is emitted in the form of gamma rays.

Due to the density of the Sun’s core – 10 times denser than silver or iron – and the state of the atoms in the core, photons can’t get sucked back in. Before leaving the core, they bounce around for 40 million years.

What is Solar Radiation

Solar radiation is the energy emitted by the sun in the form of radiation – electromagnetic waves. This energy is emitted by the photosphere, the outermost layer of the sun, which is approximately 300 km long.

It is a source of energy for the planet, and is responsible for heating it up. It is also fundamental in determining the Earth’s climate.

The volume of radiation varies according to the region of the globe: the areas that receive the most radiation are those near the Equator. The lowest levels of radiation are found in extreme areas.

How does solar radiation reach the Earth?

Solar radiation passes through the atmosphere and reaches the Earth’s surface, heating it. A good part of the radiation received is absorbed, and this part is responsible for the heating of the planet. Another fraction – the infrared – is reflected and does not reach the Earth.

The radiation that reaches the surface is influenced by the atmosphere, which filters it in different ways, according to the length of the waves.

Part of the solar radiation that reaches the Earth (ultraviolet) is absorbed by the ozone layer, a layer formed by ozone gas (O3) that lies around the Earth. It is this layer that prevents high levels of radiation from reaching the planet.

Types of solar radiation

Solar radiation is divided into three types, which are classified according to wavelengths and intensity:

  • Visible
  • Ultraviolet
  • Infrared

Visible radiation

Visible radiation gets its name because it is visible to human beings. It is the simplest form of electromagnetic radiation.

Visible radiation
Visible light

As we see in the image, it is composed of a spectrum of the following colors:

  • Red
  • Orange
  • Yellow
  • Green
  • Blue
  • Violet

Color wavelengths vary between 380 nm (violet) and 750 nm (red).

Ultraviolet radiation

Ultraviolet UV Radiation.
Ultraviolet UV Radiation.

UV (Ultraviolet) radiation contains the least amount of solar energy. Its wavelength is shorter and for this reason it is not visible.

It has three classifications, according to wavelength:

  • UVA (between 400 nm and 315 nm)
  • UVB (between 315 nm and 280 nm)
  • UVC (between 280 nm and 100 nm)

UVA radiation accounts for almost all of the ultraviolet radiation that reaches the earth. To a lesser extent, UVB radiation also reaches the surface. Both of these can cause sunburn.

UVC radiation, on the other hand, does not reach the earth’s surface due to its shorter wavelength and is completely absorbed by the atmosphere.

Infrared radiation

Picture of Infrared radiation from solar radiation.
Solar Radiation – Infrared radiation

The infrared radiation contains the largest part of the solar energy with almost 50 % and is also not visible for humans. Its length varies between 780 nm and 1 mm.

It has the property of generating large thermal motion. Therefore, this radiation can cause lesions in human tissues that consist of many water molecules, as is the case with the eyes.

Solar radiation as an energy source

Solar radiation reaching the Earth can be used for the production of energy. The result of this process is called photovoltaic energy. The generation happens by means of solar panels, formed by small silicon structures (voltaic cells).

The panels are installed in areas of high solar radiation exposure, and the energy is generated from a reaction between the photons present in the radiation and the cells composed of silicon.

The system has many advantages:

  • It is not polluting
  • Does not require much maintenance
  • Highly durable

The disadvantages are:

  • The high cost of installing the panels
  • Instability of energy production, which varies according to local climate conditions

The Yellow Sun Paradox

Who as a child didn’t draw pictures showing the sun – as a round ball with a smiling face, surrounded by a wreath of light rays? What color was the sun in your pictures? If the answer is “yellow”, you’re like me – my suns were always yellow, too. Why is that? Is the sun really yellow?

The sun is yellow.  Or not?
Is the sun yellow?

No, the sun is not yellow or golden, but white – sunlight is even the definition of white par excellence. What color is a white sheet of paper when viewed in the light of the midday sun? White. What color are cluster clouds on a sunny afternoon? White. If the sun were yellow, clouds would be yellow too, or snow in winter. A strange sight.

Why do most people perceive the sun as yellow? This has occupied quite a few authors, as a short Google search proves. Most give a standard answer, which is correct, but in my opinion incomplete. Some explanations are wrong. And one article I found also gets to the bottom of the “yellow sun paradox” experimentally.

So What Makes the Sun Yellow?

Sunlight contains photons, or “light particles” of all wavelengths and thus of all colors. However, not all photons and thus all colors occur with equal frequency. Blue-violet and red are rarer, green most common. Nevertheless, we do not see the sun as green. This is because green lies approximately in the middle of the perceptible color spectrum: There are therefore lots of photons in sunlight with shorter and longer wavelengths. These mix together, and the mixture of all the colors from red to violet gives white.

Before we see the sunlight, it has to pass through the earth’s atmosphere. And that’s where it gets exciting (again). That’s because the photons collide with the molecules of the Earth’s air envelope, changing their direction of motion in the process. “Scattering” is the physical technical term. The probability of collision is not the same for all photons. It increases the shorter the wavelength of the light particles: blue photons are scattered most frequently, red ones least frequently.

When the sunlight finally reaches our eyes, it has traveled a more or less long way through the atmosphere, depending on the position of the sun. A more or less large part of the blue photons has been “scattered away” in the process. On the one hand, the scattered blue sunlight makes the sky appear blue. And since this blue light is missing from the actual sunlight, its color shifts to longer wavelengths – thus into the yellow. This is the standard explanation mentioned above. It is correct, but not quite complete. Because the share of scattered light is not very large as long as the sun is high in the sky.

If the sun is high in the sky (like here on a winter afternoon), the light scattering in the earth's atmosphere is not enough to noticeably shift its color.  It glows white - but is too bright to be looked at directly.
If the sun is high in the sky (like here on a winter afternoon), the light scattering in the earth’s atmosphere is not enough to noticeably shift its color. It glows white – but is too bright to be looked at directly.

(Another wrong explanation claims that the yellow sun is only an optical illusion: Because the sky is blue, and blue is the complementary color of yellow, we believe that the sun appears yellow. But first, a white circle against a blue background does not automatically appear yellow, as you can try out for yourself (at least I still see it as white). Second, the white clouds against the blue sky background would then also have to appear yellowish. But they don’t.)

We approach the solution by asking ourselves when we see the sun at all – in the sense of “looking at it directly”. As long as it is high in the sky at noon, it is absolutely not advisable to look directly into the sun disk. It is much too bright. That means: For the most part of the day we can’t know what color the sun is.

Only when it is low enough in the late afternoon (or early morning) that its light is sufficiently attenuated by the effect of the Earth’s atmosphere can we risk a brief glance. Then the scattering has already disposed of a more stately part of the blue light, and the sun actually appears yellow. If it is very low above the horizon, its color even changes to red-orange.

If the sun is low above the horizon, the effect of light scattering becomes noticeable: the sun first takes on a faint, then increasingly strong yellow tone.  At the same time, its light is weakened so that you can take a quick look.
If the sun is low above the horizon, the effect of light scattering becomes noticeable: the sun first takes on a faint, then increasingly strong yellow tone. At the same time, its light is weakened so that you can take a quick look.

Sunlight Science

Optical engineer Stephen R. Wilk stressed this theory a few years ago. To do this, he modeled the change in color perception of an originally pure white light source with increasing scatter. As he reports in the magazine Optics & Photonics News (March 2009), the result corresponds exactly to the expectation described above. As soon as his model sun had sunk so far that one could risk a quick glance, it appeared yellow. And it stayed with this color until shortly before its artificial demise. Then its color swung rapidly from yellow to red due to the rapidly increasing thickness of the atmosphere.

Conclusion: The paradox of the yellow sun is on the one hand an effect of light scattering in the earth’s atmosphere. This robs the sunlight of part of its blue color and shifts its color focus from white to yellow. But it also has to do with the fact that we can only look at the sun when it is low enough on the horizon – where the color can also be seen. As long as the sun is high in the sky, it shines white – and usually much too bright to look at directly.

What If We Shot a Nuclear Bomb Into the Sun?

The sun itself is a huge nuclear mechanism. It releases every day an amount of energy equal to that of millions of atomic bombs.

A nuclear bomb will not leave the slightest trace on the sun and will not alter its activity.

Moreover, since the solar atmosphere has a temperature of thousands of degrees, the bomb and its mechanism will melt long before it reaches the sun.

All that will reach the sun is a tiny cloud of radioactive material, and that’s it.

Nuking the Sun is the same as throwing water in ocean.

75% of the Sun’s mass is composed of hydrogen atoms. Under the immense gravity and heat in the center of the star, these particles merge, creating helium atoms and releasing an enormous amount of energy.

This reaction is similar to what happens when launching hydrogen bombs, thousands of times more powerful than the bomb dropped on Hiroshima.

This process provides all the heat and light released by the Sun and allows life on Earth.

A way to signal our existence to other intelligent beings

The atomic bomb itself would have no serious effect on the sun, but if we threw a bunch of plutonium into it, other advanced societies might notice.

Plutonium is an artificial element. And would not naturally occur in the sun, so anyone who noticed it must conclude that someone else put it there.

How Was the Sun Formed?

The sun is the center of our solar system, and it is a huge nuclear reactor: inside, the fusion of hydrogen and helium generates energy at temperatures of around 15 million degrees. Temperatures of around 5700 degrees Celsius still prevail on its surface. From this surface, the photosphere, light and heat are radiated into space.

The sun – the center of our solar system

Our solar system, was formed approximately 4.6 billion years ago. It emerged from a gigantic cloud of gases and dust swirling around. The gases consisted mainly of hydrogen and some helium, the dust from ice particles and some heavy elements such as iron.

The Big Bang – a massive explosion

Now you are probably wondering where the cloud and these elements came from. The answer to this is provided by the Big Bang. About 15 billion years ago, the elements of the Big Bang emerged from nowhere. A massive explosion created space, time and matter.

The entire mass must have been united in an infinitely small and dense point of infinite heat at that moment. This highly concentrated matter suddenly exploded under enormous pressure and expanded. This is how our universe came into being. Hard to imagine, but true.

Primordial gas clouds: origin of our solar system

The elements (hydrogen, helium, iron, etc.) whirled around in an ancient galaxy for several billion years until they finally united to form a huge cloud of dust. This gigantic cloud collapsed about 4.5 billion years ago due to its own gravity.

As a result, the cloud started rotating faster and faster. Due to the fast rotation, the cloud flattened and enormous forces were released, which heated up the flat cloud.

The space in the cloud was getting narrower and the temperature was increasing. Pressure and temperature rose so much in the center of the cloud that dust particles collided more and more frequently. The temperature inside the cloud was already around 10 million degrees Celsius.

In this enormous heat, the hydrogen atom nuclei move so quickly that they melt and become helium nuclei when they collide with each other. This process is called the nuclear reaction, which means nothing other than fusion.

Nuclear reactions also existed in the cloud of gases and dust 4.5 billion years ago and ultimately led to the formation of our sun and our solar system.

The sun: the oldest and largest star in our solar system

Our sun is a self-illuminating sphere made of hot gases, which, unlike Earth, has no solid mass. With a diameter of 1.4 million kilometers, our gigantic fireball is not only the largest celestial body, but also the heaviest.

Compared to the sun, our earth appears tiny with a diameter of 13,000 kilometers. Imagine that the sun is a soccer ball and the earth is a three millimeter ball that is about 30 meters from soccer ball. The Sun to Earth ratio is roughly the same. But although the sun is 330,000 times heavier than our earth, it is not sluggish.

In 25 days the sun turns around itself and at the same time races through the Milky Way at a hell of a pace. At around 220 kilometers per second, the sun moves around the center of the galaxy, our solar system . Inside, human beings can hardly imagine temperatures of 15 million degrees Celsius and the pressure is 200 billion times higher than on Earth. The Sun has six regions:

  1. Core
  2. Radiative zone
  3. Convective zone in the interior
  4. Photosphere (the visible surface)
  5. Chromosphere
  6. Corona (outermost region)

The sun’s core – a fusion reactor

If we take a closer look at the sun, we’ll see that the structure of the sun is similar to that of an onion: it consists of several layers and peels. The core of the sun has a gigantic diameter of about 175,000 km and is a fusion reactor.

Nuclear fusion takes place here at a temperature of 15 million degrees Celsius and ten times the density of lead. A heavy helium nucleus is created from four hydrogen atom nuclei. With this fusion, mass is lost, which is converted into energy.

In just one second, the sun converts approximately five million tons of matter into energy, which it emits into space in the form of heat and light. The most important properties of the sun come from this loss of mass: light and heat.

The radiative zone

The radiative zone is located around the sun’s core. Here the energy is transported from the inside of the sun to the outside in the form of light. However, this layer is so dense and impenetrable that light and heat take a million years to reach the outside, even at the speed of light. When the sun’s rays reach our earth, they are already ancient.

The convection zone

If we move further away from the core of the sun, the temperature drops to “only” three million degrees Celsius and we reach the next layer – the convection zone. The following happens there: Due to the “low” temperature, the energy can no longer be carried to the surface as radiation.

Instead, glowing chunks of matter, so-called granules, rise to the sun’s surface. Here they cool down and sink back into deeper layers. This process is called convection.

Brightest layer: the photosphere

The subsequent layer is called the photosphere. It is the visible surface of the sun and relatively cool at around 6,000 degrees Celsius. This zone consists of a 400 km thick layer of gas that is not solid but impenetrable.

In the photosphere, the energy from the inside is given off as visible radiation, which is why it is also called the brightest layer.

The sun’s atmosphere – two hot gas shells

The chromosphere and the corona together form the solar atmosphere. The chromosphere joins the photosphere as the next layer and is also called the color sphere. It got this name because of its reddish bright color. Here the temperature rises again to around 10,000 degrees Celsius.

The chromosphere is up to 10,000 kilometers high and consists of individual gas jets. The outermost layer of the solar atmosphere is formed by the corona. This zone consists of very thin gas. You can only see the corona during a total solar eclipse.

Then it appears as a white, shining light ring around the darkened sun. The temperature in this layer rises again to several million degrees Celsius.

The sun: facts and figures

  • Mass: 1,989,000,000,000,000,000,000,000,000,000 kg (330,000 times the mass of the earth).
  • Diameter: 1,392,000 km (the earth would fit 109 times around the sun).
  • Age: 4,500,000,000 years.
  • Estimated life: 10,000,000,000 years.
  • Core temperature: 15,000,000 ° C.
  • Temperature in the photosphere: 5,500 ° C.
  • Energy radiance: 383,000,000,000,000,000,000,000,000 watts.
  • Distance to Earth: An average of 149,600,000 km (the distance is different because the Earth’s orbit around the Sun is oval).
  • Components: 75% hydrogen; 24% helium; 1% carbon, oxygen, small amounts of 63 other elements.

How does a solar eclipse occur?

When the sun darkens in the middle of the day it feels like the end of the world has arrived. During solar eclipses, the moon moves between the earth and the sun and partially or totally obscures it.

It is probably the most dramatic spectacle that the sky has to offer us: the sunlight becomes pale, the crystal clear daylight transforms into twilight. Then, as if someone turns off the light on the dimmer, everything happens very quickly. The brightest stars flare up and where the blazing bright sun was just visible, there is now a pitch-black circle in the sky, surrounded by a fiery, finely structured ring of light. A total solar eclipse!

There are three kinds of solar eclipses:

  • Total eclipse
  • Partial eclipse
  • Annular eclipse

In a total solar eclipse, the moon moves exactly between the earth and the sun, so that the sun is completely covered. The solar eclipse is only total from places that lie along a very narrow strip on Earth. This path of totality (track of the Moon’s shadow across Earth’s surface) is a maximum of a few hundred kilometers wide and many thousand kilometers long.

During partial solar eclipses only part of the sun is covered by the moon. An annular solar eclipse occurs when the moon appears smaller than the Sun as it passes centrally across the solar disk. During such an eclipse a bright ring of sunlight remains visible.

How is total eclipse possible if the moon and sun are not the same size?

The fact that eclipses can be total is due to a unique coincidence in the planetary system: the sun and moon appear practically the same size in the earth’s sky. The diameter of the sun is actually about 400 times larger than that of the moon. But since the sun is about 400 times further away from the earth than the moon, both appear to be about the same size.

There are up to four solar eclipses per year (two of which are total), but a specific location on Earth only benefits from a total solar eclipse once every few hundred years. The last total solar eclipse occured in July 2019 and was visible from the Pitcairn Islands, central Argentina and Chile, Tuamotu Archipelago of French Polynesia. The next total eclipse will take place in December 2020 and will be visible to the residents of Southern Chile and Argentina, Kiribati and Polynesia.

Partial solar eclipses are much more common: only part of the sun is covered by the moon. The sun is not completely “swallowed” by the moon, but only “bitten”.

Attention! The observation of solar eclipses should only be done with special glasses. Never look directly into the sun with binoculars or a telescope. The consequences would be severe eye damage up to blindness.

The sun’s corona

During a total eclipse of the sun, the dark moon disk is surrounded by a bright, spectacular ring of rays. That is the corona, the atmosphere of the sun. The gas, which is a million degrees hot, is normally outshone by the bright sun. Only when the moon covers the sun disk can the corona be seen with the naked eye.

Solar eclipses are largely of no interest to astronomers today. The sun can always be observed very well in telescopes and with satellites – also with the help of “artificial” eclipses in telescopes. However, some solar researchers are still examining the areas of the corona close to the sun’s surface during total eclipses. These deep areas of the sun’s atmosphere can hardly be observed otherwise. Ancient records of solar eclipses are of great importance for geophysics. Because knowing in which regions on earth which eclipses could be seen can be used to determine the gradual slowdown of the earth’s rotation.

The moon during solar eclipse

A solar eclipse can only occur on a new moon. However, not every new moon gives us an eclipse. Because the moon’s orbit is inclined by about 5 degrees to the Earth’s orbit around the sun. Therefore, the new moon usually runs from above or below the sun. We only experience a solar eclipse when the new moon is exactly in the plane of the earth’s orbit.

In optimal conditions, total darkness lasts a maximum of seven and a half minutes. The longest eclipse that people currently living on Earth could see took place in China and the West Pacific. It lasted 6 minutes and 39 seconds.

Solar eclipses 2020

Calendar Date Eclipse Type Central Duration Geographic Region of Eclipse Visibility
2020 Jun 21 Annular 00m38s Africa, se Europe, Asia (Annular: c Africa, s Asia, China, Pacific)
2020 Dec 14 Total 02m10s Pacific, s S. America, Antarctica (Total: s Pacific, Chile, Argentina, s Atlantic)

Source: NASA eclipse website

Related articles:

What is a lunar eclipse? Three types of lunar eclipses.

What are Stars? A Short Introduction.

How old is the moon and how did it form?

What would earth be like without a moon?

Why is the moon visible during the day?