The following slides are for use with UCAR Center for Science Education’s The Magnetic Sun classroom activity
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Make your own magnetometer (a tool to detect magnetic fields)
What you’ll need:
Make your own magnetometer (a tool to detect magnetic fields)
Step 1: Lay a pin across the sticky side of a piece of tape.
Step 2: Add a second pin facing the opposite direction. (If the heads of the pin stick out further than the points, the points won’t poke you.)
Step 3: Lay one end of the thread across the pins and tape, oriented perpendicular to the pins.
Step 4: Fold the tape over
so that the pins are in the crease.
Make your own magnetometer
Step 5: Push the thread all the way through the straw.
Step 6: Hold the straw vertically. Adjust the length of the thread so that the taped pins dangle just below the bottom of the straw. Make sure the pins do not touch the straw.
Step 7: Fold the free end of the thread over onto the outside of the top of the straw and tape it into place.
Step 8: To magnetize the pins, stroke them lengthwise with one pole of the magnet.
Step 9: Check to see if the pins point toward the magnet when you hold it close by.
The image on the right was taken through a filter that allows light through from the center of the calcium absorption line. This particular wavelength of light is emitted from layers higher up in the solar atmosphere called the “chromosphere.” Small magnetic features appear bright and form either large bright regions called “plage,” from the French word for ”beach,” or an interconnected pattern called “network.”
These images were taken by the Precision Solar Photometric Telescope at Mauna Loa Solar Observatory in Hawaii. They show how the Sun looks at two different wavelengths of light. By using filters to observe the sun at particular wavelengths, solar physicists are able to study structures in the solar atmosphere.
The image on the left was taken through a filter that allowed only blue light through. It shows the photosphere of the Sun, the layer from which most of the light we see freely escapes into space. In this image, sunspots are visible as dark patches because they are cooler and emit less intense light. Also, visible on the image are faint patterns due to convection motions in the Sun’s surface layers.
These images show examples of enormous sunspots. The one on the left shows an image of the entire Sun to demonstrate how big the spots can get (sometimes as big as several Earth diameters across). The image on the right shows a close up view of a large sunspot. A sunspot is a large concentration of strong magnetic field. In the dark central part, called the “umbra,” the magnetic field is nearly vertical. In the gray surrounding region, called the “penumbra,” the magnetic field lies more horizontal. A sunspot is darker than the background because it is cooler and emits less light at most wavelengths. It is cooler because the presence of the strong magnetic field inhibits the convective motions (boiling motions) found in the outer layers of the Sun. These motions, visible as granules surround the penumbra, transport the heat produced inside the Sun to the surface layers, where it radiates away. If the convective motions are restricted, the heat is transported less efficiently. The penumbra is less dark than the umbra because the weaker horizontally-oriented magnetic fields in the penumbra inhibit the motions less than the strong vertical fields in the umbra do.
A solar flare is a dramatic release of stored-up solar magnetic energy into the solar atmosphere. It is a sudden brightening across a limited region of the sun. Radiation is emitted at virtually every wavelength from radio to visible to x-ray. The biggest solar flare observed to date occurred on November 4, 2003.
The first solar image shows the flare as a bright flash in extreme ultraviolet radiation (EUV). Flares are classified based on their brightness in x-ray emission. The graph of x-ray flux versus time shows that flare on November 4, 2003, was the fourth flare and biggest so-called “X” class flare occurring over the course of a few days.
Erupting prominences are perhaps the most common type of solar activity associated with coronal mass ejections (CMEs) and may play a fundamental role in the formation of CMEs. This is an image of a large, eruptive prominence as seen in ultraviolet light with an image of the Earth added for size comparison. Solar prominences are relatively cool, high density material suspended in the solar atmosphere. This prominence from July 24, 1999, is particularly large and looping, extending over 35 Earths out from the Sun. Erupting prominences are often components of CMEs and can affect communications, navigation systems, and power grids while also producing auroras visible in the night skies.
In general, the magnetic field, like gravity, acts to hold down the solar atmosphere. The temperature of the solar corona is millions of degrees (much greater than the solar surface of 5,500˚C). These high temperatures and the presence of stresses on the coronal magnetic field act to drive the atmosphere outward. Previously closed magnetic regions can become unstable resulting in a sudden ejection of coronal plasma and magnetic field into the solar wind, known as the Coronal Mass Ejections (CMEs).
This set of images shows a CME from 10:04 to 13:34 on August 28, 1980. Large ejections, such as the one pictured here, send upwards of 1013 kg of coronal material into space at rates of 100 km/s or more (although average values are closer to about 1012 kg and 400 km/s). The CME originates from a helmet streamer – the bright, pointed feature seen in the lower half of the first two images of the sequence – which is blown out by the passage of the CME. When CMEs are Earthward directed, they can affect communications and produce auroras visible in the night skies.
On the left is an image of a total solar eclipse on February 26, 1998. The image on the right is a computer model of the Sun’s magnetic field as it would appear on the same day. The bright coronal regions in the eclipse image correspond to the locations in the corona where the solar magnetic field is shaped like loops (i.e. closed), as seen in the model image on the right. These magnetic loops act to trap the solar atmosphere so that great amounts of material are located in these regions causing them to appear brighter. The darker regions in the eclipse image are locations where the solar corona escapes the Sun to form the solar wind, which fills the solar system. The magnetic field lines in these darker regions are drawn out into the solar system (as seen in the model image on the right) and become part of the solar wind.
The image on the left is the solar corona seen in visible light in an artificial eclipse taken on November 1, 2003. The light from the solar disk is about 1 million times brighter than the corona, so the white light corona can only be seen in “eclipsed” images. Visible light images of the corona allow scientists to map the density structure of the corona and are ideal observations for tracking coronal mass ejections (CMEs). The corona can be detected out to great distances (more than 10 million miles) when viewed in visible light from telescopes in space.
The image on the right is the solar corona in extreme ultraviolet (EUV) light taken by the Extreme Ultraviolet Imaging Telescope (EIT) on the SOHO spacecraft. In this type of light, scientists can view the corona against the solar disk. No artificial eclipse is needed because the solar disk is dark in EUV wavelengths. EUV images allow the scientists to study the temperature and density structure of the corona and track features as they rotate across the disk of the sun. These observations are ideal for studying solar flares and other coronal disturbances.
The polarity of the Sun’s global magnetic field reverses about every 11 years, forming a complete cycle about every 22 years. The amount of magnetic field present on the Sun varies with time, increasing and decreasing with a fairly regular period of 11 years. The number of sunspots visible on the Sun at any one time reflects this cycle, as seen in the central plot of the above figure, but that is not the only change which occurs. The whole solar atmosphere adjusts to the changes in surface magnetic field distribution. The top row of images are x-ray images of the Sun taken with the Yohkoh spacecraft. They show the decrease in x-ray output of the Sun as the magnetic activity decreases at the end of a solar cycle. The bottom row shows how the outer solar atmosphere, called the corona, changes with the solar cycle. When few magnetic sunspots are present on the Sun, called solar minimum, the closed (bright) regions of the corona are confined to lower latitudes centered around the solar equator. At solar minimum, the global magnetic field on the sun resembles a simple dipole field, like that produced by a bar magnet. When many magnetic regions are present, the corona appears more symmetric, with closed (bright) structures located at all latitudes.