The Sun

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About this Image

This image of the brightness distribution of the Sun shows that the bright features, the solar active regions, form two bands symmetric about the solar equator. Each active region corresponds to a volume in the corona, in the vicinity of but above sunspots, in which high density, hot material is confined by strong magnetic fields (hundreds of Gauss). All radiation is probably due to thermal bremsstrahlung. The brightness temperatures of the brightest regions are 2.4 x 106 K, about the same as the kinetic temperatures in the active regions; these sources are probably optically thick at 20 cm. Other active regions are less bright, probably because the density is lower and the optical thickness is less than unity., Away from active regions are quiet regions of moderate brightness (50,000 to 100,000 K), where the coronal kinetic temperature is about 106 K but the density is low enough that the corona is optically thin and most radiation is from the cooler transition region. Regions of very low brightness (less than about 50,000 K) are coronal holes and filament cavities, regions where the corona is of especially low density. Off of the limb of the Sun are wisps which are due to instrumental sidelobes.

Investigator(s):  G.A. Dulk, D.E. Gary

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Technical Data

    Telescope VLA 
    Date of Observation 1981-09-26 
    Type of Observation Continuum Observations 
    Band L 
    Wavelength 20 cm 
    Frequency 1.4 GHz 
    Field of View 0.6667 x 0.6667 degrees  
    Technical Caption VLA - D-configuration using 27 antennae. Ten hour synthesis. The zero spatial frequency component was added from a separate measurement with a small antenna. Spatial frequencies less than 1200" were added by assuming a uniform disk 32' in diameter.  


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