THE SUN'S CROWN

Why does a burning candle not look as bright in daylight as it does in a dark room? Well daylight is much brighter than the candle and it swamps the light from it making it hard to see. The same thing happens with the Sun's atmosphere.

The Sun's atmosphere, which we call the corona, is made of very hot gas and stretches far out into space. It scatters light from the Sun in all directions. This scattered light is dim compared to the light coming directly from the Sun and because of this we can't normally see the corona or CMEs. During a total solar eclipse however, the Sun's disc is covered by the moon and the Sun's atmosphere becomes visible as a shining ring around the moon. Since this shining ring reminded people of a crown it was called the corona, which means crown. So the Sun really is King (or Queen, ed.) of the solar system! Image courtesy of the High Altitude Observatory, Boulder, USA.

Thanks to a Frenchman named Bernard Lyot (here seen working at a telescope in a photo from the Pic du Midi observatory in France) who invented the coronagraph in 1930, we can look at the corona anytime we want. Remember that a coronagraph is just a telescope with a disc that blocks out the bright light from the Sun and lets us see the surrounding corona.

However, even though Lyot's coronagraph was a great invention, we always get a better look at the corona from space because there is no air and no clouds! The coronagraph on SOHO is called LASCO and it gives us an amazing view of the corona, better than ever before and much better than watching a total solar eclipse. This helps us in our work to figure out how the Sun works.

WHAT DOES THE CORONA LOOK LIKE USING MODERN SPACE INSTRUMENTS?

LASCO has three telescopes called C1, C2 and C3. This gives us three different views of the corona. During the quiet time of the Sun's cycle most of the gas in the corona is in long features called coronal streamers. These stretch a long way into space like arms and look bright because they contain a lot of hot gas that scatters the Sun's light.

Image courtesy of the LASCO/SOHO consortium. SOHO is a mission of international cooperation between of ESA and NASA.

The corona's million degree temperature means that it emits light. This picture from the LASCO C1 telescope shows this light (C1 works differently than C2 and C3 which both record scattered light). The magnetic field that comes from the Sun forms the gas into large arcs. C1 shows us what the corona looks like from near the Sun's surface out to about two or three million kilometres.

Image courtesy of the LASCO/SOHO consortium. SOHO is a mission of international cooperation between of ESA and NASA.

This picture, taken by the LASCO C2 telescope shows the corona in the range 1.3 to 4.0 million kilometres from the Sun. The C2 telescope records light that is scattered from the electrons in the corona. Most of the gas is concentrated into three long streamers.

Image courtesy of the LASCO/SOHO consortium. SOHO is a mission of international cooperation between of ESA and NASA.

This is a picture taken by the LASCO C3 telescope which also records scattered light from the corona. The C3 telescope shows us what the corona looks like from about 4 million to 21 million kilometres from the Sun! Again most of the gas is concentrated into three very long streamers (remember the white circle in the middle marks the position of the Sun and shows its size). The black streak in the picture is caused by the post that holds the occulting disc in place.

Longer than 2,000 Earths placed side by side!

When the Sun gets more active so does the corona. We see many more streamers and more CMEs!

Image courtesy of the LASCO/SOHO consortium. SOHO is a mission of international cooperation between of ESA and NASA.

Follow this link to see a movie (QuickTime, 2Mb) of the Sun's atmosphere in playful mood!