2003 SPACE SCIENCE VIDEOTAPES |
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Tape Title | Record ID | Date Produced | TRT: |
Synopsis |
| THE SUN DOES THE WAVE | G03-003 | 01/03/03 | 00:003:33 | Like fans doing the wave at a stadium, large cell-like features called supergranules are propagating around the Sun like a wave, giving the illusion of the solar surface rotating faster that other features, such as dark sunspots, etc. Thanks to new research from the Solar and Heliospheric Observatory (SOHO) spacecraft, scientists now have their answer for the strange rotation rates they had observed.
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TAPE CONTENTS: |
| ITEM (1): Doing the Wave
- An instrument on the SOHO spacecraft shows that the apparent 'superrotation' of the supergranules is due to the fact that they propagate like a wave. Like in a stadium, people don't move in the direction of 'the wave' - just up and down. This artist's conception shows a band of supergranules rotating faster across the Sun's surface than other features, such as dark sunspots. This occurs everywhere on the Sun's surface, but is simplified to a narrow band here to highlight the phenomenon.
Courtesy: NASA
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| ITEM (2): Doppler Shift - The thousands of cells called supergranules that cover the Sun's surface are most easily visible in "dopplergrams." A dopplergram, such as this one from the SOHO spacecraft, shows motions on the Sun's surface with areas moving toward us appearing dark, and areas moving away, bright. This image is the result of averaging 30 velocity images and subtracting the Sun's rotation, and can also be thought of as a map of the speed of the Sun's surface. Supergranules are large convection cells, measuring around 30,000 km across (about two Earths across) but their origin and depth is currently unknown. The lifetime of an individual supergranule is about 2 days.
Courtesy: NASA/ESA
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| ITEM (3): Rotation Anomalies
- The Sun's rotation is not constant like Earth's - rather a complete solar rotation is 27 days at the equator but about 35 days at the poles. This phenomenon is due to the Sun's gaseous composition - such a 'differential' rotation would be impossible on the solid Earth. With the mystery of the supergranular rotation solved, the overall rotation rate of the Sun is unchanged - the illusion had only a very small influence on the Sun's rotation observed by scientists.
Courtesy: NASA /ESA
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| ITEM (4): SOHO Spacecraft - The Solar and Heliospheric Observatory (SOHO) operates at a vantage point of about 1 million miles out in space between the Sun and Earth. One of its 12 instruments, the Michelson Doppler Imager (MDI) allows scientists to use sound waves inside the Sun to diagnose our star's internal conditions and even see the far side of the Sun. SOHO launched in 1995 and among its functions, provides advance warning of potentially dangerous solar activity.
Courtesy: NASA/ESA
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