The Sun

When we see the sun, all we see is a big, round very bright object in the sky. In fact, it is so bright that it is dangerous to look at it unless you have special glasses on -- its brightness can damage your eyes.

Our sun is a star. There are billions of stars just in our galaxy alone -- the Milky Way Galaxy. And there are billions of galaxies out there, each with billions of stars. Our star, our sun, is not a giant star, but it is big enough for us. It 1,390,000 km across, or about 868,000 miles across. Just as a comparison, our own earth's diameter is about 8000 miles. That means we could fit about 108 earths across the middle of the sun.

From where we are in our solar system, our moon and the sun look about the same size, as demonstrated above. However the size of the sun seems very different on the other planets.

sun size diagram

From what we can see of the sun, on its surface, we find about 70% hydrogen, 28% helium, and only 2% of other elements.

When we look more closely at the sun, we find it has layers.

sun layers

If you look at the temperatures listed in this picture, you will find something strange -- something that has fascinated scientists for years: the further you go out in the layers, the hotter the temperatures get.

When we glance at the sun, what we see is simply called the photosphere. It's that thing that looks big and round. But when we block out that part, we can see the other layers. The two layers of the chromosphere '(chrome' means 'color') are just ouside the photosphere, and far above all that stretches the corona (which means 'crown'), which can only be seen during a full eclipse of the sun.


The above illustration shows what layers can be seen during a full eclipse (when the moon blocks out the sun). On the left we can still see the edge of the photosphere as a bright white crescent. In the middle, that has been covered by the moon and the chromosphere is visible. When the brightness of both the photosphere and the chromosphere are fully covered, we can finally see the very large corona surrounding both. Below are photographs of both the chromosphere (left) and the corona (right) during a full eclipse of the sun.

chromosphere corona

The sun, like the earth, rotates -- it goes around and around. It goes around in the same direction the earth does, from west to east. But the sun, the same as the outer four planets (which are called "gas giants"), doesn't rotate the same way earth does. Because the earth is solid, the poles and the equator rotate the same way -- they are always lined up with each other. Because a circle around at the north or south pole is very small compared to the circle around the middle, at the equator, the rate of spin at the equator is much faster, but any spot near the north or south pole will always line up with the same spot at the equator as the earth turns.

The sun is very different. It has a thick gas outer section which rotates at different speeds. The middle, the equator part, rotates much, much faster than the gases at the poles spin around the axis. A spot on the sun's equator will spin all the way around the sun in 25.4 days. However a spot near one of the poles will need 36 days to make its complete circle. In other words, the middle is spinning faster than either the north or south poles. This is called differential rotation.

The surface of the sun is not calm -- it is a seething mass. Here are some of the other things we see:

sun surface


Sunspots appear as dark spots on the sun's surface. They always come in pairs. They are actually holes in the surface of the sun which allow us to look down a bit into the sun's interior. There is an interesting note about the temperature here, too -- the sunspots have a lower temperature than the surface of the sun. That was not expected. The temperature in the center of the sunspots measures about 3800-4200 Kelvin (about 6400 - 7000 degrees Fahrenheit); the surrounding surface is about 5800 Kelvin (about 9900 F.). That is thousands of degrees difference! (Some stars are not even as hot as the middle of our sunspots)

sunspot group

The picture above shows a close-up picture of a sunspot through a filter, so we aren't blinded by the glare. The middle part, the black part, is called the "umbra." It is surrounded by the brown (in this picture) filaments (string-like structures) called the "penumbra." What looks like crumpled gold foil as 'background' are "granules" on the surface, or "photosphere" of the sun.

Typically, sunspots are the size of the Earth, or even larger, and frequently appear in groups or solar active regions. The number of sunspots on the sun's surface rises and falls between a maximum and a minimum over an 11year cycle. During a solar maximum there can be as many as 200 spots on the sun's surface. During a solar minimum there are very few, and sometimes none at all. 2013-2014 was a time of solar maximum, however this maximum was not as active as many before it, and there were relatively few sunspots.

Sunspots are associated with magnetic fields in the photosphere. Groups of sunspots can grow or fade over a few days or weeks. There are usually also a greater number of solar flares during the time of the solar maximum.

For about sixty years, between 1645 and 1715, there was so little solar activity that Europe experienced what is referred to as the "Little Ice Age." Winters were so cold the River Thames in England froze over. The less sunspot activity, the colder the earth becomes; the more sunspot activity, the warmer it becomes. Men have nothing to do with this

Munder minimum

When sunspot numbers are high, more heat comes from the sun and warms the earth around the equator. The water around the equator heat up a bit and,because of that, releases more carbon dioxide (the same way a bottle of soda does if you open it and leave it in a warm place). Again, this rise in carbon dioxide during periods of high sunspot activity has nothing to do with anything men are doing on earth. It is a natural phenomena. Because the temperatures at the poles remain the same, there are stronger air exchange currents going from the equator to the poles and back again, as the warmer air rises and the cooler air rushes in to fill the gap. This is the major cause of storms becoming worse during these times.

What is interesting is that, although we just finished a period of high sunspot activity in 2013-2014, the sunspot activity was not very high at all, so there was none of the 'global warming' we have been warned about. That is why those who are trying to make laws about our activities to try to stop global warming had to change the term from "global warming" to "climate change." The truth of the matter is that there is nothing we can do about the sun's activity. We can stop polluting the earth and the air, yes, but we canot change the sun's activity.

Sunspot maxima correspond generally to periods of high solar activity. This activity includes increased solar wind and phenomena like aurorae and magnetic storms that are correlated with the solar wind, increased flares and prominences, and increased non-thermal radio and X-ray emission. Conversely, near sunspot minima the Sun is much quieter with respect to these phenomena. In addition, as we have seen there are significant differences in the nature of the corona during periods of active and quiet Suns. (The Sunspot Cycle)

Solar Flares

Solar flares are sudden, rapid, and intense variations in the sun's brightness. They are explosive bursts of the energy stored in sunspot's magnetic fields. Their radiation is emitted across virtually the entire electromagnetic spectrum, from radio waves at the long wavelength end, through the optical emission to x-rays and gamma rays at the short wavelength end.

electromagnetic spectrum


Flares last from a few minutes up to an hour, and send particles out into space. This shot of particles is called a coronal mass ejection. When a coronal mass ejection interacts with earth, it can cause power outages and computer breakdowns. The amount of energy released in a solar flare is the same as millions of 100-megaton hydrogen bombs exploding at the same time. As the magnetic energy is being released, particles -- including electrons, protons and heavy nuclei -- are heated and accelerated into the solar atmosphere.

The requency of flares coincides with the sun's susnpot cycle. When the solar cycle is at a minimum, active regions are small and rare and few solar flares are deected. These increase in number as the sun approaches the maximum part of its cycle.


solar flare

Solar Granules

The surface of the sun is covered by what appears to be a mottled pattern. This grainy appearance is due to millions or even billions of "bubbly" areas which appear and disappear rapidly. These are called "solar granules," and they become visible from Earth when seeing conditions are excellent. The granules are up to 650 miles across. The two different models each have a different explanation for them (this is discussed in the "Explanation" section).

solar granules

the above picture is shown in motion here

Granules can come together to form supergranules, which are larger cells up to 30,000 km (about 19,000 miles) across and can last for several hours. At the edges of these supergranules, fiery spikes can arise, shooting up to10,000 km (about 6000 miles) into the chromosphere. These fiery spikes are called Spicules. More than 100,000 spicules cover the sun's surface at any one time. Nevertheless, there is no way of predicting just when or why one will occur. All we know is that magnetic fields are involved. Spicules burst from the sun's surface at speeds of up to 50,000 miles per hour (or about 15 miles every second). These supersonic jets rush forth with great consistency, but they have relatively small diameters of only about 300 miles. (If you think about this in terms you can understand, these spicules are very tall and skinny. If they were only 3 feet wide, they would be 60 feet tall, or as tall as a six story building).



Solar Prominences

Whereas spicules are 'little spikes' compared to the size of the sun, solar prominences are huge. They shoot up far above the sun's surface and often fall back again. They appear as luminous reddish gas clouds in the corona, often with arch shapes that follow the lines of both the sun's and the sunspots' magnetic fields. When we see them on the edge of the sun, they look like this:

solar prominence


If you look at the photograph above, you will also see some dark 'snaky' lines. That is what a solar prominence looks like if we don't see it edge on. When we only see the dark lines, they are called 'filaments.' Sometimes the sun ejects the material so forcefully that it does not fall back into the sun, but streams out into the solar system.

The bright white spots are solar flares.

The Solar Wind

The sun releases into the solar system vast amounts of positive particles, mainly hydrogen nuclei, or protons. This is called the solar wind, and it could be very damaging to earth if we did not have the protection of our own ionosphere (plasma sphere). This will be discussed in detail later. The solar wind strength is related to sunspot maxima and minima, increasing during a sunspot maximum and decreasing during a sunspot minimum.

A great YouTube video of a a solar prominence, and the material ejected,with a lot of it falling back into the sun, is here.

Solar Eruption on YouTube -- strongly suggest to leave it on mute!

Three Years of the Sun in Three Minutes, on YouTube