Peering Through the Layers (May 13, 2004)
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The five images of the Sun (seen in the video clip) were taken on May
12, 2004 at about the same time. Every day SOHO views the solar
atmosphere in normal or white light and at several wavelengths
of extreme ultraviolet light in order to reveal the structure and
activity of solar material at different temperatures, which
consequently means different altitudes above the surface. It's almost
like peeling away layers of an onion to see what the layer underneath
looks like, though some features overlap so it is a bit more
complicated than that.
In the order they appear in the video there is a progression from the
coolest to the hottest temperatures of material being observed. These
are:
- the orange continuum image of the Sun's surface, about
6,000 degrees K. (This misses a lot of the activity in the corona that
the other images reveal.)
- the (red-orange) image in a spectral line of singly ionized helium
was taken at 304 Angstroms (top right), at 60,000 to 80,000 degrees
Kelvin;
- in the (blue) image at 171 Angstroms, ions of iron are viewed at
about 0.9 - 1.0 million K. (8 and 9 times ionized iron)
- in the (green) image at 195 Angstroms, again ions of iron are
viewed at about 1.5 million K. (11 times ionized iron);
- in the (yellow) final image at 284 Angstroms, ions of iron are
viewed at about 2.0 - 2.5 million K. (14 times ionized iron).
Different features are viewed at different wavelengths. We want the
differentiation in temperature so we can understand the flow of energy
among features in the solar atmosphere, and what kinds of energy
(thermal, mechanical, electromagnetic) are involved in creating,
sustaining, and destroying the features. The brighter areas usually
indicate a higher density of material, and thus, greater magnetic
activity. All the images are digital, and record only the intensity of
the light in the given bandpass. The colors are used for quick
identification and to remind people that EUV radiation, like visible
light, is composed of a variety of wavelengths -- colors -- that can
tell us different things.
Previous Picks of the Week
SOHO began its Weekly Pick some time after
sending a weekly image or video clip to the American Museum of
Natural History (Rose Center) in New York City. There, the SOHO Weekly Pick is displayed with some annotations on a large plasma display.
If your institution would also like to receive the same Weekly Pick from us
for display (usually in Photoshop or QuickTime format), please send
your inquiry to steele.hill@gsfc.nasa.gov.
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