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STEREO -- a new tool for DXers
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by AA6YQ on May 14, 2009
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Mail this to a friend!
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Solar flux is the product of sunspots on the sun's earth-facing hemisphere. From our perspective on earth, the sun rotates every ~27 days. When a sunspot rotates out of view, we can assume/hope that it will appear again on sun's opposite limb ~13.5 days later, but it could shrink or disappear during that interval. New sunspots can form on the solar hemisphere facing away from earth, rotating onto the earth-facing hemisphere as much as 13.5 days later.
In October 2006, NASA launched two spacecraft destined for solar orbit: one ahead of the Earth, and the other trailing behind. Their objective is "to trace the flow of energy and matter from the Sun to Earth, and to reveal the 3D structure of coronal mass ejections". This mission, known as STEREO, also provides alerts for Earth-directed solar ejections, because the two satellites provide a view of the solar hemisphere not visible from earth. They also detect sunspots.
At present, the spacecraft known as Ahead is 48 degrees ahead of earth in its solar orbit, and the spacecraft known as Behind is 47 degrees behind earth. In the diagram on this web page, Ahead is labeled A in red font, and Behind labeled B in blue font:
<http://stereo.gsfc.nasa.gov/where.shtml>
Due to its location, Behind gets a preview of what's about to rotate into the sun's earth-facing solar hemisphere. With a 47 degree separation, that preview is (47/360)*27 => 3.5 days. Ahead and Behind will continue to separate; two years from now, Ahead will be 90 degrees ahead of earth in its solar orbit, and Behind will be 90 degrees behind earth. This will provide a complete view of the solar hemisphere facing away from earth, enabling us to monitor the birth, growth, shrinkage, and death of sunspots there without interruption.
This web page shows the latest solar images from Ahead and Behind:
<http://stereo.gsfc.nasa.gov/>
Behind's image shows a new spot on the left about to rotate onto the earth-facing solar hemisphere, adding to the flux now being generated by the two spots on the right. Expect a solar flux in the range of 76-78 by this weekend.
STEREO should provide DXers with an excellent tool for predicting solar flux.
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