Visibility of ISS

[Belisarius]

This morning I went out to watch the ISS as it passed over Barcelona. Visibility was good, and the ISS was magnitude -2.6 just before dawn. When I saw it, I could almost swear I saw the outline of the structure, not just the pinprick of light I'd seen before. I was using x75 binoculars.

Is this possible? Or was it my imagination?

 

[Lunar Pilot]

I don't know

I don't know, you could have, I've looked all over Google and I can't find anything.

 

[YL3GDY]

Well, let's calculate a bit. Size of ISS is about 100m. Distance to ISS from your position will be about 500 km (may be more, but likely not less).
We'll have anglular size of ISS about tan(50/500000) = 10^(-4) rad = 0.00061 angular seconds.

By the way, which binoculars have you used (aperture, focal length)? Visual size of ISS is too small for most binoculars.

Regards,
Alex.

 

[Belisarius]

Thanks Alex, you convinced me that I couldn't have seen it in such detail. I'm not exactly sure of aperture and focal length, but 0.0006 arc seconds is way too small for me to see with my little binocs. Sadly I brought a telescope that could have done it, maybe, but I didn't get enough time to set it up.
I'll remember to have a strong cup of coffee before I do it next time.

Cheers
B

 

[Chode]

This morning I went out to watch the ISS as it passed over Barcelona. Visibility was good, and the ISS was magnitude -2.6 just before dawn. When I saw it, I could almost swear I saw the outline of the structure, not just the pinprick of light I'd seen before. I was using x75 binoculars.

Is this possible? Or was it my imagination?

It is possible to see a little detail when looking at the ISS through good binoculars. The actual size is something like 40 arcseconds at closest approach (YL3GDY's calculation is a little bit off). I myself haven't had great results, but then I need to get better binoculars.

Regards

 

[Andy44]

It may just be possible to make out that what you're seeing is not a point source of light, but it may also be that you're seeing what you want to see. The ISS is amazingly bright, I once watched it pass over my house in the evening and the sky was still blue. It's not hard to imagine you're seeing apendages like solar panels and such when really you're just seeing a star pattern as if looking at streetlight through a fogged-up window.

 

[Kyle]

Well, wonder what'd be like to have it like this in your telescope. This is a no joke image from a telescope.

 

[Belisarius]

I definitely didn't see that

 

[Lunar Pilot]

x

If we could see that with a telescope, then why would we have so much trouble in looking at other planets with the same telescope?

 

[Quick_Nick]

Trouble? Use that telescope and I'm thinking it wouldn't be too hard to see a giant sphere.

 

[Chode]

A good test of your binoculars (and your eyesight) is to observe Jupiter. Coincidentally, it has an apparent angular size similar to the ISS of about 40 arcseconds. If you can detect that Jupiter is a spherical body rather than a point of light, then you should also be able to see some details when you look at the ISS.

Regards

 

[Lunar Pilot]

Answer

Well, you do have a pesky thing called an atmosphere blurring everything.

 

[ijuin]

Yes, but the photo in this thread is taken from the ground, so the atmosphere can't be that bad when there's no dust or moisture in the way.

Also, 10^-4 radians should be something like twenty arcseconds--there are about 57 degrees in a radian and 3600 arcseconds in a degree, which makes about 216,000-220,000 arcseconds in a radian.

 

[Messierhunter]

Yes, but the photo in this thread is taken from the ground, so the atmosphere can't be that bad when there's no dust or moisture in the way.

Also, 10^-4 radians should be something like twenty arcseconds--there are about 57 degrees in a radian and 3600 arcseconds in a degree, which makes about 216,000-220,000 arcseconds in a radian.

It's not just dust and moisture you have to worry about, it's the atmospheric seeing as well. Now that photo was taken with a rather large telescope (obviously), but I have to wonder if they were using some kind of adaptive optics as well in order to compensate for seeing, perhaps by using an "artificial star" (laser).

The only alternative is that they got lucky with a very fast camera and managed to catch a brief moment of incredibly steady seeing. Webcam astrophotographers use the latter method to take amazing shots of the planets, but because they're trying to be selective in what frames to stack and what frames to discard, it can take several minutes at least to accumulate an averaged image that looks good. You don't have that kind of time with a space station pass; in a telescope the station's perspective shifts so fast that even after just 1 second it's moved too much to keep stacking images.

A friend and I managed to get this image with my 8" schmidt-cassegrain -

Obviously I'll never be able to approach the clarity of the amazing image above, but I still want to get my "dream shot" before they retire the shuttle - a shot of the shuttle next to the station right after undocking or right before docking. It's been done at least once before, and I nearly pulled it off myself once (I overexposed it, doh!), but I want to get it at least as clear as this shot here.

 

[agentgonzo]

It's not just dust and moisture you have to worry about, it's the atmospheric seeing as well. Now that photo was taken with a rather large telescope (obviously), but I have to wonder if they were using some kind of adaptive optics as well in order to compensate for seeing, perhaps by using an "artificial star" (laser).

It was a 25" Ritchey-Chretien at the Clay Centre Observatory. I don't think it has adaptive optics.

http://apod.nasa.gov/apod/ap070628.html
http://www.dexter-southfield.org/podium/default.aspx?t=11309

 

[Belisarius]

Given all the limitations you explain, the Messierhunter photo is a real achievement. Good work! Wish I had the patience.

BTW, I tried the Jupiter test and my binocs aren't good enough but my lightweight telescope is... So time to go ISS hunting again

 

[Messierhunter]

It was a 25" Ritchey-Chretien at the Clay Centre Observatory. I don't think it has adaptive optics.

http://apod.nasa.gov/apod/ap070628.html
http://www.dexter-southfield.org/podium/default.aspx?t=11309

Apparently they do have some level of adaptive optics:
http://blog.wired.com/defense/2007/06/picture-this-sp.html
"The folks at the Clay Center Observatory did it with a 25-inch diameter telescope in combination with a digital video camera -- and nothing but the simplest "adaptive optics" (bendable mirrors, which correct for how the atmosphere warps the light)."

Kind of an oxymoronic statement; there's nothing "simple" about adaptive optics. That said, it may not be a primary mirror adjustment, but rather a camera-side accessory, similar to the AO-7.
http://www.sbig.com/sbwhtmls/ccdacc.htm#MODEL%20AO-7%20ADAPTIVE%20OPTICS%20SYSTEM

 

[agentgonzo]

Apparently they do have some level of adaptive optics...

That was the only quote that I could find that mentioned adaptive optics. Even their own website doesn't mention that they have adaptive optics. Bloggers aren't the most reliable source.

 

[Lunar Pilot]

adaptive optics

How in the world would you get such a good picture like that without adaptive optics? It's practically impossible.

 

[Messierhunter]

That was the only quote that I could find that mentioned adaptive optics. Even their own website doesn't mention that they have adaptive optics. Bloggers aren't the most reliable source.

Someone on satobs.org has also confirmed that they have adaptive optics. This person says it's a two axis system, which fits well with what the wired article said it was - "simple" adaptive optics. A tilt/tip mirror system would be an example of a two axis system, basically the same idea as the commercially available AO-7, but it was probably designed to work with a much faster camera for doing "lucky imaging" on satellites.
http://www.satobs.org/seesat/Jun-2007/0379.html