"Coronagraph" just refers to an instrument which studies the Sun's outer
atmosphere, the "corona". From Earth this is most easily seen during a
total eclipse. SOHO have two coronagraphs which study the Sun from
space.
A very common way to observe the corona is to cover the bright disk of
the Sun. This creates a sort of mini-eclipse and allows us to see the
Sun's fainter outer atmosphere.
One of the coronagraph instrument on SOHO, LASCO actually
contains three coronagraphs, each with a different sized occulting disk
so that we can see the fainter and fainter corona, further and further
away from the Sun's surface.
Another of SOHO's coronagraphs, UVCS, doesn't
use an occulting disk - it just shifts its pointing around the Sun,
avoiding the Sun's disk
Below are images from the three LASCO coronagraphs and UVCS. The white
circles show the size and location of the Sun's surface. As with much
SOHO data, the color isn't "real". We color code the images so we can
tell them apart quickly.
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LASCO C1 | LASCO C2 |
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LASCO C3
The dark line on the lower left is the
support for the occulting disk. | UVCS |
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Ground Based Coronagraphs
It is possible to use coronagraphs from the top of a tall mountain on
Earth as well, although you can't see the corona as far from the solar
disk as you can in space. Below are examples of coronagraph images taken from the Earth.
