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Space Shuttle and ISS transit the Sun.

apod.nasa.gov

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Re: Space Shuttle and ISS transit the Sun.

#4

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.)

This page gives a bit more explanation, particularly the filters used on the camera (which would be a necessity to reduce the glare and intensity of the sun enough to resolve something like the ISS + shuttle):

http://www.astrosurf.com/legault/iss_atlantis_transit_2010.h...

Re: Space Shuttle and ISS transit the Sun.

#6

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.)

The sun probably isn't in focus.

I don't know what infinity is for a lens like that, but it's probably further away than LEO.

Re: Space Shuttle and ISS transit the Sun.

#7

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.)

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.

Re: Space Shuttle and ISS transit the Sun.

#10
post #3

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

On that day, there were no visible sunspots:

http://soi.stanford.edu/production/gif_images/intensitygrams...

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

http://soi.stanford.edu/production/gif_images/intensitygrams...

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

http://soi.stanford.edu/production/gif_images/intensitygrams...

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

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