Slashdot Mirror

Only a little bit. The solar spectrum from earth and space are extremely well known. A space based look is definatly the most useful, but accounting for our own atmosphere isn't all that hard.

NASA's logo is attached to the article, but the National Solar Observatory is funded by the National Science Foundation. Different agency entirely. http://www.nso.edu/

The parent comment is an amusing narratve, but if we wanted to find some holes in it....

1) The article is in regard to a large stellar flare, not a solar one. Currently the Sun is at solar minimum, and while large solar activity can occur at this time of the cycle, such activity is rare. For those that are interested, the National Solar Observatory has images of the current solar activity, and a current space weather report is available from the Space Environment Center. Besides all of that, the flare the article is referring to was detected close to a year ago.

2) Even if the storm referred to were from our own star, most of the effects of solar activity do not reach Earth for several days (especially those that affect our electronics). Coronal mass ejections (CMEs) are large amounts of charged particles that can interact with our magnetic field causing geomagnetic storms. These particles take numerous hours to several days to travel from the Sun to Earth. On the other hand, radio interference can happen as soon as the storm is detected (8 minutes after the event). But even then, the antennas usually need to be pointing toward the Sun in order for the SNR to be low enough for problems.

Does anyone know if this was a fallen GONG satellite?

The GONG is used to watch the Sun oscillate, or "ring," which provides mighty useful data on the solar interior. Helioseismology, in other words. See http://gong.nso.edu for details.

Credit Line: The GONG is operated by the National Solar Observatory which is operated by the Association of Universities for Research in Astronomy under a cooperative agreement with the National Science Foundation, for the benefit of the astronomical community.

The GONG is used to watch the Sun oscillate, or "ring," which provides mighty useful data on the solar interior. Helioseismology, in other words. See http://gong.nso.edu for details.

Credit Line: The GONG is operated by the National Solar Observatory which is operated by the Association of Universities for Research in Astronomy under a cooperative agreement with the National Science Foundation, for the benefit of the astronomical community.

Speaking of which here is a fast mirror.

How does the cameras sensors not melt and achieve good accuracy by staring into the sun ? Surely they must be cooled off, but how ?

Oddly enough, the CCD's generally are not cooled at all. The amount of light falling on the detector is actually not that great. Remember that each pixel corresponds to less than 0.1 x 0.1 arcsec, which means it covers about one-billionth of the solar surface (and hence the flux is one billion times less than integrated sunlight). Then you start taking very small slices in wavelength (0.01 nm or less, compared to the 100's of nanometers over the sun's emission peak in the visible wavelengths). Toss in a polarizer too (though they didn't use one in these observations), and next thing you know, you are running out of photons! That's why we need a big (by solar telescope standards) 4-meter telescope like the ATST ( http://atst.nso.edu).

The exposure times in observations like these are also very short, on the order of 20 milliseconds or less, so there is no time for the dark current to build up during a long exposure (this is why nighttime CCD's, with exposures of minutes or hours, are often cooled). For some applications, even simple video rate CCD's can be used (the problem often being the small number of pixels).

As you might surmise, even if the detector isn't getting hit with that many photons, a lot of extra light is going through the telescope. Getting rid of waste heat IS a problem, and, as is the case with the Swedish Tower, often the main body of the telescope (entrance aperture -> main mirror -> instrument feed) is kept in a vacuum to reduce currents from heated air in the optical path. However, the Swedish Tower appears to be at the limit for the size of the entrance window (must be of optical quality and with minimal stress) that can be used (the entrance window is the size of the main lens on the Yerkes telescope - the world's biggest refractor). That is why bigger telescopes like the GREGOR (1.5 m) and ATST (4 m) will be open, like nighttime telescopes, and will have to use different methods of thermal control. We can't go bigger than four meters now because of the limits of our thermal control capabilities.

You can build your own spectroscope and see the spectral lines in sunlight with:
- Piece of diffraction grating, the non-aluminized, see-through kind
- Box that toothpaste came in
- Tape and office supplies

Cut a round 1-cm hole in one end of the long, squarish box. Tape the diffraction grating over it.

Cut a narrow slit, with an X-Acto or similar knife, in the other end.

Now go look at something that lights up by heating gas. This would be either the sun or a fluorescent light, or a mercury-vapor light, etc. Look through the end with the diffraction grating. Compare the sun with a fluorescent--That's one of the ways they can tell what's in a star without going there.

Here's how to build a bigger one with some links, but the toothpaste box one, you can carry around and impress your friends. (One way or the other.) Link from that page about a spectroscope made from an old CD.