

Space Shuttle and ISS transit the Sun. - RiderOfGiraffes
http://apod.nasa.gov/apod/ap100523.html

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petercooper
Astronomy types.. how comes the Sun looks so smooth and simple in this picture
whereas it looks almost "volcanic" and highly irregular in most other pictures
I've seen? (Just do a Google Images search for "sun" to see loads of them.)

~~~
mturmon
The simple reason is that the photo was imaged with a filter that admitted a
wide band of spectrum ("continuum" or "white light").

The science images you see are with very narrow filters, which pass light of a
very-very specific color. These filters are typically about 1nm wide, the
range of visible light is hundreds of nm (380-750nm). The Sun emits a lot of
photons, so it's no problem to filter them out.

Why do they look in these narrow bands? When you do so, you see only plasma at
a certain temperature range -- by varying where the tiny passband is, you see
different cross sections of heated plasma. This turns out to be very useful to
understand the solar atmosphere and in particular the corona; the coronal
heating problem
(<http://en.wikipedia.org/wiki/Corona#Coronal_heating_problem>) is the major
unsolved problem in solar physics.

A good scientific explanation of the remote sensing problem is at:

<http://aia.lmsal.com/public/firstlight.html>

The story of these bands is fascinating. See

<http://en.wikipedia.org/wiki/Astronomical_spectroscopy>

and

<http://en.wikipedia.org/wiki/Fraunhofer_lines>

As a teaser, before the quantization of spectra was known, it was considered
impossible to ever know the chemical composition of the Sun. What are you
going to do, land there and take a sample back to the lab?

Shortly thereafter, spectroscopy was understood and helium was discovered on
the Sun (helium -- helios) _before_ being isolated on Earth. The laugh was on
the pundits, and now we know the composition of stars all over the galaxy.

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ugh
Those Astronomy Pictures of the Day are well worth exploring. Here is the Moon
and Venus as you might not have not have seen them before (well, at least
Venus): <http://apod.nasa.gov/apod/ap100516.html>

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praeclarum
Fantastic photo. Now if only we had the foresight to make the ISS more
substantial. It looks like a bug ready to be squashed. Makes me think we're in
the dark ages of space research, a long ways from the eventual renaissance.

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Estragon
I saw this when it came out and thought "someone's been reading _Anathem_ "

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alexforget
deepzoom version of the same kind of stuff <http://alex.bouncingbox.com/iss/>

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pencil
kinda unbelievable..no sun spots or any other form of solar activity

~~~
mturmon
On that day, there were no visible sunspots:

[http://soi.stanford.edu/production/gif_images/intensitygrams...](http://soi.stanford.edu/production/gif_images/intensitygrams/2010/May//MDI_int_2010.05.16_06:24.rotated.gif)

But, a week later when it made APOD, there was a big one:

[http://soi.stanford.edu/production/gif_images/intensitygrams...](http://soi.stanford.edu/production/gif_images/intensitygrams/2010/May//MDI_int_2010.05.23_11:12.rotated.gif)

Here's a very active day from a peak in the last cycle:

[http://soi.stanford.edu/production/gif_images/intensitygrams...](http://soi.stanford.edu/production/gif_images/intensitygrams/2001/September//MDI_int_2001.09.23_03:12.gif)

These are not true white-light images, but they are approximations. Also,
their contrast has been enhanced.

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sachbh
wow! great picture

