Every 11 years, the Sun cycles through increasing and decreasing energetic activity. When activity is at a peak, the number of sunspots increases. Major explosions burst from the surface - some as powerful as a billion atomic bombs. If you were to observe the Sun using your sunglasses, though, you wouldn’t notice much of the change, even at the peak of activity. Why? Because these energetic changes aren’t happening within the visible band of the electromagnetic (EM) spectrum.
Our eyes are tuned to a narrow energy band of light, the visible band of the EM spectrum. The entire spectrum ranges from very long-wavelength, low energy light to short-wavelength, high-energy light. The bands of the spectrum, in order of increasing energy, are: radio, microwaves, infrared, visible, ultraviolet, X rays, and gamma rays. Most of the solar activity scientists want to observe isn’t detectable within the visible band of the spectrum. Instead, scientists want to “see” in the ultraviolet band. More specifically, they want to see in the EUV or “extreme ultraviolet” band.
You probably have heard of ultraviolet rays, or UV light, in the context of sunburns. Indeed, regular UV light can be damaging to living tissues. Extreme UV is even more energetic, and, lucky for us, the atmosphere blocks extreme UV rays. For scientists who want to observe changes in the Sun’s energy output, extreme UV is the perfect energy band in which to collect data.
NASA’s “EVE” sensor – short for “EUV Variability Experiment” observes the Sun from on board the Solar Dynamic Observatory satellite. During the Sun’s active phase, extreme UV emissions can change by many orders of magnitudes over just a few minutes, causing “space weather” that even Earth-bound satellites can experience. Extreme UV emissions can also shear atoms apart, creating free ions that can interrupt radio and other signals.
The EVE mission constantly monitors and track the Sun’s extreme UV emissions. Interestingly, it was launched during a time of solar calm, when activity is at a lull. This will provide a useful neutral point of comparison – or baseline - for later in the Sun’s cycle when activity will intensify. By comparing cycle-to-cycle maxima of energetic brightness, scientists have theorized that, overall, the Sun’s energy is dimming and its total irradiance (energy emitted) is slowly decreasing. The EVE project will help confirm or refute this theory by adding much more data to scientists’ view of the Sun.
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Classroom Activity: Solar Cycles
Students plot the solar cycle between 1996 and 2007 in three wavelengths from three different EM bands: one infrared, one visible, and one extreme UV. Plots should compare intensity across the three wavelengths over the given period. Students then describe what the three profiles have in common and how they are different. Suggested data source: Solar Data Analysis Center, NASAS Goddard Space Flight Center
Discussion Questions: Do the cycles match for each of the bands? If so, why? If not, why not? Are the differences between the bands less pronounced during periods of overall low or high energy? How will the data from EVE affect a future version of this inquiry? How do you think the solar cycles you plotted would correlate with space weather?
Students can visit NASA's Solar Dynamics Observatory (SDO) web site to learn more and to get a Real-time look at the Sun.
Solar irradiance is the energy hitting the earth from the sun. We have different kinds of solar irradiance. We have heat solar irradiance, which is the infrared radiation. We have the visible light, which is what we can use to see and what makes plants grow. We also have ultraviolet light, which is absorbed by our ozone layer, and we also have x-ray and extreme ultraviolet, which is quite harmful and thankfully absorbed much higher up in our atmosphere.
EVE is the Extreme Ultraviolet Variability Experiment. It will measure the solar irradiance in the extreme ultraviolet, which is very short wavelengths that are absorbed completely by the Earth's atmosphere and never make it to the surface. They also are quite deadly, and can hurt people and electronics that are out in space. They cause the atmosphere to heat up and expand and bring down spacecraft. And also, it causes radio communications to be interfered with.
EVE will measure the solar irradiance at these wavelengths very rapidly-- about every ten seconds--allowing us to use that for warning people about the dangers of flares, for putting them into the models that tell us what's happening to the atmosphere, and to also allow people that are doing radio communications and navigation to know that there could be a problem with their system because of what the sun just did.
Academic standards correlations on Teachers' Domain use the Achievement Standards Network (ASN) database of state and national standards, provided to NSDL projects courtesy of JES & Co.
We assign reference terms to each statement within a standards document and to each media resource, and correlations are based upon matches of these terms for a given grade band. If a particular standards document of interest to you is not displayed yet, it most likely has not yet been processed by ASN or by Teachers' Domain. We will be adding social studies and arts correlations over the coming year, and also will be increasing the specificity of alignment.