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Scientists See Through Sun For First Time
By Maia Weinstock
Staff Writer
posted: 07:30 am ET
10 March 2000
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Something about the Far Side of the Sun Its not quite X-ray vision, but Superman would be proud. For the first time ever, scientists have actually seen through the sun and created accurate images of its far side, the side we cant see from Earth. The breakthrough was made possible with data from SOHO, a European Space Agency/NASA satellite in stationary orbit between Earth and the sun. "This is an absolutely marvelous result," said Craig DeForest, a solar physicist at Southwest Research Institute in Boulder, Colorado. Researchers say the far-side solar images will greatly improve predictions of solar gas ejections, which can have crippling effects on spacecraft and communication systems on Earth. "This is as exciting as when the first pictures of the moons far side were released," said U.S. SOHO project scientist, Joseph Gurman. "It makes you think:' Wow, its the first time human beings have actually extended their reach to the far side of the sun.'" Being able to monitor the suns far side will give researchers at least one weeks advance notice of solar gas ejections, which until now were hidden almost completely from view until they rotated around to the suns near side. (A technique that uses reflected light from features in a gas cloud around the sun has been used make crude predictions of solar storms, but this method is extremely imprecise.)Howd they do that? In the March 10, 2000 issue of the journal Science, Charles Lindsey and Douglas Braun, researchers at Solar Physics Research Corp and NorthWest Research Associates in Boulder, Colorado, introduced the secret to far-side solar imaging: sound waves. Like seismologists who study pressure waves to figure out where an earthquake or nuclear test occurred on Earths surface, Lindsey and Braun created images of the suns far side by charting naturally occurring sound waves, which are seen as slight distortions on the suns surface. 
| In this image, an active region on the side of the Sun facing away from the Earth (the far side) causes sound waves, represented by blue arcs, that travel through the interior, bounce once off the surface, and reach the side facing the Earth (the near side). The waves generate ripples on the near side surface and are reflected back toward the active region. |
When the suns gases convect, they make noise in the same way bubbles bursting in a pot of boiling water make noise. But these noises permeate the entire sun, crossing through the interior from one side to the other. In this way, noises created on the suns far side generate ripples that researchers can see on the suns near side surface. Lindsey and Brauns new imaging technique used the Michelson Doppler Imager on board the SOHO spacecraft to observe sound wave ripples on the suns near surface. Lindsey and Braun were then able to use solar physics laws to convert these sound wave ripples into images of the solar far side. "We reconstructed the path of sound waves back to their far side source kind of like running a movie backward." explained Lindsey."Doctors Lindsey and Braun have exploited the fact that the sun is basically a great sphere of sound waves in order to determine information about the far side," added DeForest. "Its like were looking right through a star." Solar weather forecasting Why do scientists want to know more about the suns far side? For one thing, the far side is where currently unpredictable eruptions of solar gases originate. These eruptions can swoop by Earth and interact with our atmosphere when they rotate around to the solar near side, often causing major disruptions in communications systems and power grids. Scientists now know that sound bursts indicate areas of surface activity. As a result, being able to image sound bursts on the suns far side will alert researchers to solar events that could come around and hit Earth days to weeks later. "We can actually now predict when and where theres going to be a solar active region, a place where mass solar ejections originate," said Gurman. "We can also say whether a new region is likely to be the kind to produce solar storms that could have some effect on Earth or near-Earth space." Long-range space weather forecasting can benefit a wide variety of Earth-based activities. In the past several decades communications satellites and electric power transmitters have been strongly affected as a result of large-scale solar storms. Spacecraft in orbit near Earth are also susceptible to damage from the suns charged particles, as are astronauts who are either are docked in a space station, in orbit around Earth, or traveling to the moon or a planet. Advanced warning about large ejections of solar energy could help scientists shield spacecraft and people from danger. Currently, solar storm warnings can be made from SOHO data a couple of days in advance of the event. Lindsey and Brauns technique, which will available to scientists on a permanent basis sometime in the next few years, uses available technology to increase that advance warning time to at least seven days. For now, the future of space weather probes looks promising. NASA and the European Space Agency are already planning to launch a total of six different spacecraft over the next 10 years. The focus of these probes will include predicting space weather, understanding solar activity and learning how variations in solar storms affect climate on Earth.
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