Planetarium Program
part II for
The Sun in Time

sun_in_time_ssm.jpg (10439 bytes)

Just as the shamen of yesteryear made careful observations of their environment, today's modern solar scientists are also observers.  The scientists of today however, use tools such as telescopes, satellites, and space probes instead of sticks, stones, or pyramids.  Certain types of filters on telescopes allow the scientist to study the Sun in various wavelengths of light (see slide show page 8).  Here is a picture of the Sun taken through an ultraviolet filter, at 171 Ångströms with an instrument aboard the TRACE spacecraft. The TRACE spacecraft obtains frequent images at a variety of wavelengths. To see the most recent ones, press here.

For a larger, 66KB image, click on the thumbnail image above.

The sun emits many different types of radiation. Light is a type of radiation which we classify by wavelength.  Visible light, is in the range of 4000-7000 Ångströms (an Ångström, symbolized by Å, is a unit of wavelength equal to 10-10 m, named for Swedish scientist Anders Jonas Ångström).   What other types of radiation can you think of?

{Infrared, which would be wavelengths greater than 7000 Å, and Ultraviolet (UV), wavelengths less than 4000 Å, are common responses from eighth graders, but there's also x-ray and gamma-ray radiation.}

Infrared radiation which is invisible to the eye may be felt as heat. A person standing next to you, an electric heater, or a fire radiates in the infrared.  If you can feel heat from an object without actually touching it then you are likely feeling infrared.  Ultraviolet light, can also be detected by your skin, but as sunburn. Sunscreen and sunglasses work by blocking ultraviolet.  Not only can UV cause serious burns to your skin, but it can also damage your eyes. It is deceptive since it cannot be seen or immediately felt.  Because of this, it is very important to never look directly at the sun; permanent damage could result.  However, if it weren't for the light (All the wavelengths of light) from our star the Sun, the Earth would be an ice cube in space.  Imagine the oceans frozen all the way down! 

Because of the dangers of UV radiation, you will hear more warnings about viewing the sun when there is a total solar eclipse. Solar eclipses occur whenever the Moon moves between the Earth and the Sun, thus blocking the light of the Sun.  During the partial phases of an eclipse, all wavelengths of light from the sun are lessened in intensity, but there is still enough ultraviolet radiation to damage the eyes.

Aug. 11, 1999 Eclipse -- First Contact (31 kb)

Aug. 11, 1999 Eclipse -- Partial Phase (32 kb)

Aug. 11, 1999 Eclipse -- Totality (58 kb)

Aug. 11, 1999 Eclipse -- Totality (450 kb)

Since the intensity of all light is reduced, the body's natural response is also reduced. For example, under normal conditions, when you catch a pop fly in a ball game and you accidentally catch the sun in your eyes, the pain, a natural response meant to protect you, causes you to quickly shut your eyes.  But during an eclipse, you are more likely to look longer at the Sun, possibly damaging your retina. 

Here at the Von Braun Astronomical Society, we look at the sun using an indirect method: sunlight is reflected by a mirror onto a screen.  Using this technique, we can safely see sunspots on the surface of the sun.  Galileo Galilei, the first western astronomer to observe sunspots with a telescope, didn't use the indirect method and possibly went blind as a result.  Don't ever use smoked glass or any other thing like that to view the Sun, only indirect methods are truly safe.  But back to the sunspots.  Sunspots are dark regions on the Sun, as you can see in the picture.  The spots appear dark because they are cooler than their surroundings, with temperatures of about 4000 Kelvin (K) as opposed to 6000 K.  (The Kelvin temperature scale is related to the Fahrenheit and Celsius scales as follows: 273 K = 0C = 32F.)

{To convert from Fahrenheit to Centigrade or Centigrade to Fahrenheit, C = 5/9 * ( F - 32) or F = (9/5*C) + 32. }

By using a special instrument called a spectroscope, a device which separates light into its component colors, astronomers discovered (in the early 1900s) that sunpsots are areas with very intense magnetic fields.  Because the magnetic field of these spots can become twisted and thus store energy (like twisting a rubber band); eruptions associated with these sunspots sometimes occur on the surface of the Sun.  These eruptions are called solar flares.

A solar flare radiates large amounts of energy in many wavelength bands, over a relatively small amount of time (typically minutes to hours).  Eruptive activity of this type can be very disruptive to modern society, especially when the flare is accompanied by a coronal mass ejection (CME).  The most dangerous products of CMEs are rapidly moving electrons and protons. Electronic connections on satellites and the space shuttle, radio communications, and even power stations on the surface of the Earth -- all can be disrupted by a "solar storm."

{For more information, see Sun in Time slide show page 5 and Sun in Time slide show page 6.}

Here on the surface of the Earth, we enjoy the protection provided by the atmosphere as well as by its magnetic field.  Because of the existence of the Earth's magnetic field, people close (greater than approximately 40 degrees North or South latitude) to the North and South Poles may be treated to a phenomenon called aurora, or Northern (Aurora Borealis)/Southern (Aurora Australis) Lights.  The charged particles (electrons and protons) which were emitted from the Sun during solar storms, interact with the magnetic field of the Earth (the Ultraviolet Imager Page) to create these aurora.  Occasionally, when there is a very large solar storm, aurorae can be seen as far south as Miami, Florida (about 25 degrees North latitude).

Our active sun, with all its spots and flares and CMEs, is just one of many stars. So, as long as we are here in the planetarium, let's try to become more familiar with the "suns" of the night.

{ Go to part 3 }

To go to Part III of the Planetarium Program, click here .

To return to Planetarium Program Part I, click here.

To return to the Slide Show Index, click here.

To return to the Sun in Time home page, click here.