Part 2
Posted by
JAC on 2/5/2010, 7:13 am
Finally - and of most immediate relevance for Earth--SDO will observe the sun at wavelengths where the sun is most variable, the extreme ultraviolet (EUV). EUV photons are high-energy cousins of regular UV rays that cause sunburns. Fortunately, our atmosphere blocks solar EUV; otherwise a day at the beach could be fatal. In space, solar EUV emission is easy to detect and arguably the most sensitive indicator of solar activity.
"If human eyes could see EUV wavelengths, no one would doubt that the sun is a variable star," says Tom Woods of the University of Colorado in Boulder.
http://www.youtube.com/nasaexplorer#p/a/u/0/BthDupBQXpQ
During a solar flare, the sun's extreme ultraviolet output can vary by factors of hundreds to thousands in a matter of seconds. Surges of EUV photons heat Earth's upper atmosphere, causing the atmosphere to "puff up" and drag down low-orbiting satellites. EUV rays also break apart atoms and molecules, creating a layer of ions in the upper atmosphere that can severely disturb radio signals. According to Judith Lean, "EUV controls Earth's environment throughout the entire atmosphere above about 100 km."
"EUV is where the action is," agrees Woods.
That's why Woods and colleagues built an extreme ultraviolet sensor for SDO called the EUV Variability Experiment ("EVE"). "EVE gives us the highest time resolution (10 sec) and the highest spectral resolution (< 0.1 nm) that we've ever had for measuring the sun, and we'll have it 24/7," he says. "This is a huge improvement over past missions."
Woods expects EVE to reveal how fast the sun can change-"we really don't know," he points out-and to surprise astronomers with the size of the outbursts.
EVE, AIA, HMI. For the next five years, the Solar Dynamics Observatory will use these instruments to redefine our star and its potential for variability. What unorthodox ideas will they beam back? Old teachings beware!
Author: Dr. Tony Phillips | Credit: Science(at)NASA
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JAC,
2/4/2010, 5:53 am Post A Reply
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