Pictures of the Sun at different radio frequencies

Click on an image for an expanded view.

Radio image of the Sun Radio image of the Sun Radio image of the Sun

The leftmost image is at the lowest frequency, 0.33 GHz (wavelength of 1 meter), and arises high in the Sun's corona, i.e., the hot atmosphere which lies above the Sun's visible surface. The bright spot to the right is a place high in the atmosphere where electrons are being accelerated to high energies. The Sun looks elongated at this frequency because of the large difference in density of gas between the outer corona above the Sun's poles and the corona at the Sun's equator. Although it doesn't look like it in these thumbnail images, the Sun "looks" bigger at this frequency than it does at the higher frequencies shown in the other images (check the scales in the larger images you see by clicking on the individual frames).

The middle image is taken at 1.4 GHz, and penetrates lower into the atmosphere where hot dense regions known as active regions become visible. These are the sites of activity in the Sun's atmosphere, and the gas in these regions is particularly hot. The cause of the heating which makes the Sun's corona so hot (millions of degrees) is still not understood and is an active area of research for astronomers who study the Sun.

The rightmost image is taken at 5 GHz and penetrates deeper still into the atmosphere. Here the brightest radio emission comes from a sunspot from which strong magnetic fields rise up into the solar atmosphere. The long dark lines on the east (left) limb of the Sun are due to some unidentified cool filaments of material trapped in the atmosphere above the surface, whereas the long dark line to the right of the Sun is a region where there is very little gas in the corona.

All these image were made with the Very Large Array radiotelescope in New Mexico, operated by the National Radio Astronomy Observatory.