What differences do you see?

If you do not see a picture of the Sun below, you need to get the Java 1.3 plug-in to run the Applet. Click here for instructions to download it from java.sun.com and install it.

The image labelled "Visible, Magnetic, 525 nm., Mt. Wilson" is actually the magnetic component of the EMR, in a visible frequency emitted from sodium. The blue is positive, green strongly positive; red is negative and yellow is strongly negative. White is neutral. This indicates the polarity of the turbulence. As the solar convection cells boil, the plasma becomes magnetically polarized. Notice how the large blue and red areas match up to the active violent areas in the other wavelengths.

When you repeat this with many pairs of images, in many wavelengths, you can get a good idea where the energy level peaks. Remember the black body distribution?

Not all the bright spots line up! What appears dark in visible light appears bright in infra-red and X-ray. Of course, this is how scientists decided to colorize the images. They can choose any color they like, of course, for the images in the non-visible frequencies because, remember, those frequencies don't have any 'color'. Yet one common principle in colorizing is that the intensity of the EMR determines the intensity of the color representation.

Look at the image in visible light from Stanford University. Choose that image in both boxes. This is the closest to what you would see if you looked through your backyard optical telescope with a sun filter. See how the sunspots are darker? Those areas are really very hot, but since they are not as hot as the areas around them, they are colored darker. Why are they cooler, you ask? Now you are thinking like a scientist. The answer is that strong magnetic fields lie under the surface, blocking the flow of energy in those areas. Those are shown as the red and blue areas on the Mt. Wilson image.

Let's do an exercise to learn more...With the Stanford image in the background, overlay it with one from a lower frequency, say the Infra-red from Kitt Peak. See how much larger those dark areas are, and how many more of them there are? Now, as an overlay, choose the higher frequency, EIT, 17.1 nm. See how the sun spots are now bright hot areas? Now choose for the background, the magnetogram from Mt. Wilson. Again the spots align. To understand what is happening here, think about what happens when you put your finger under a running water faucet and try to block the water. You end up spraying water out the sides, right? And it can go pretty far too. The magnetic fields are like your finger, blocking the flow of energy from the layers below, to the 'surface' that we see, called the 'photosphere'. Yet some of the energy does escape and just like the spraying water, is propelled much higher. It is so concentrated, that it hits the upper layers, called the 'corona' which it heats up to temperatures much hotter then the photosphere. This is what scientists call solar flares, prominences and can even cause coronal mass ejections. When they are aimed at Earth, our satellites have to close their shutters to protect their instruments, because the radiation can cause great damage. These occurences also are responsible for Earth's polar auroras, known as the 'Northern Lights'.

Can you see the letter 'J' in the Sun?

Did you notice the dark river-like objects on several of the images? One in the shape of the letter 'J' appears on the Meudon image and several others. These areas show cool condensations in the upper atmosphere. The condensations typically form along magnetic loops. When they are seen off the solar disk, they show up as the prominences. Projected against the disk, they are dark in these filters because, being cooler than the matter below, they absorb the radiation. Remember reading about absorption lines on the 'Spectroscopy' page? The darks lines, then, are the shapes of gas plumes above the solar disk, in our line of sight with the Sun.

All the telescopes and satellites try to stay very steady. Yet there are differences between the images. They were taken at different times on the same day. You can see the timestamp, in Coordinated Universal Time, in the choice boxes. The rotation of the Sun and the movement of the solar material account for some of the differences. The orientation of the camera is another factor.

The image from the Yohkoh satellite was taken late in 2001. The satellite has not been transmitting images since then. I included this image because I wanted you to see how it was colorized, and how large the x-rays spread away from the photosphere.