Air glow over Germany

[Phil Bunch]

Quite a remarkable photo from space.

http://apod.nasa.gov/apod/ap120905.html

Probably they just picked up effects from Hardy's work on PSX!

[Hardy Heinlin]

Impressive photo, I like it.

(I also like the appearance of Andromeda, it's always so big and bright even with bare eyes.)


|*|

[Will]

10-second exposure? Just guessing.

[Hardy Heinlin]

You're guessing the red line comes from an aircraft at a ground speed of 500 knots at FL330 which makes a 5° arc on the firmament if flown for 10 seconds? :-)


... hmmm, I think the distance flown is much longer. 10 seconds is not enough, I guess. Or it's a satellite. But it's red.

[Avi]

The red line (even though it's red) is probably the International Space Station or any other big object in space. The ISS can be very easily seen from earth with a naked eye (saw it and even space shuttles many times).

[frumpy]

Judging from the number of stars and the milkyway, I assume
exposure would have been several minutes at ISO 800 or higher.
Once I did a 2 minute exposure at midnight and ISO 200
(so thats 30s at ISO 800), it truly captured all information
available, it was all black :-D

[Will]

The exposure isn't long enough for any of the stars to start leaving a streak (with the caveat that the stars in the upper-right look like lens distortion rather than a rotational artifact).

What's the longest-duration exposure that would still leave stars looking as points? That would give us a maximum value for the exposure.

[Phil Bunch]

Is it possible that the red streak is just a meteor trail?

Re estimating exposure time, current practice for astrophotography often uses many short exposures and then adds them up in the computer.  This way, one gains on key signal-to-noise ratio limitations, and one also avoids atmospheric turbulence related image blur.  Amateur astrophotographers have captured surprisingly good photos of the planets this way, for example.  I am unsure if this technique would be applicable or relevant to photographing earth from space.  At first thought, I would think that atmospheric turbulence would be the same problem if one were photographing from space or earth.

[Shiv Mathur]

The description on that nasa page calls it a 'streaking airplane'.

But of course, even they can be wrong!

shiv

[Hardy Heinlin]

Re estimating exposure time, current practice for astrophotography often uses many short exposures and then adds them up in the computer.  This way, one gains on key signal-to-noise ratio limitations, and one also avoids atmospheric turbulence related image blur.

Interesting. I guess the exposures take only a few milliseconds then? Otherwise, it wouldn't make sense as the atmospheric turbulence wobbles rather quickly. And when adding the pictures up, the software probably shifts each of those fine and sharp dots to a common pixel coordinate? Otherwise, due to the random turbulence, you would get a dotted cluster of each star?


Cheers,

|-|ardy

[Phil Bunch]

Re estimating exposure time, current practice for astrophotography often uses many short exposures and then adds them up in the computer.  This way, one gains on key signal-to-noise ratio limitations, and one also avoids atmospheric turbulence related image blur.

Interesting. I guess the exposures take only a few milliseconds then? Otherwise, it wouldn't make sense as the atmospheric turbulence wobbles rather quickly. And when adding the pictures up, the software probably shifts each of those fine and sharp dots to a common pixel coordinate? Otherwise, due to the random turbulence, you would get a dotted cluster of each star?


Cheers,

|-|ardy

Hardy,

I believe this link provides a basic summary of how astrophotography image stacking works, and its basic benefits:

https://en.wikipedia.org/wiki/Speckle_imaging

Using modern, low-noise digital image sensors, which are often cooled (even by amateurs) to lower the thermal sensor noise, has made a big difference for this and related techniques.

Another recent technique that has helped work around atmospheric turbulence is adaptive optics.  Here, one uses a laser beam to create a synthetic "guide star" in the field of view for rapidly mechanically distorting the telescope's mirror to compensate for atmospheric turbulence.  I believe that the basic paradigm is to observe and then in real time to compensate for the observed blur of the laser beam's tiny spot, using many fast, extremely precise localized mechanical mirror adjustment devices.  Needless to say, a *lot* of physics, computing, optical engineering, and years of effort went into perfecting these systems.  I am not sure if anything like this is currently available for amateur astronomy.  Here's a wikipedia link:

https://en.wikipedia.org/wiki/Adaptive_optics
------------------------------------------

Things have changed quite radically since the "good old days" when everyone had to make film-based astrophotographs...  

I worked as a staff scientist at the Kodak Research Labs (specializing in medical radiography) until retiring in 2006.  I became casually acquainted with a highly regarded scientist at the Kodak Research Labs who worked full-time on film-based astrophotography.  He provided his expert assistance to observatories as well as working with other film R&D staff to improve and better understand astronomical photographic materials.  I soon decided that he surely had one of the best staff scientist jobs available at Kodak, since he was able to work closely with leading astronomers as well as helping to improve these very specialized photographic materials.  Here's a link to a 1986 retirement announcement:

http://adsabs.harvard.edu/full/1986AASPB..42....1.

and

http://articles.adsabs.harvard.edu/full/seri/AASPB/0042//0000011.000.html