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Full Version: Does ISS cast (moving) shadow ?
Unmanned > EVA > Manned Spaceflight
I've red, a long time ago, that only 3 celestrial bodies cast shadow on Earth : Sun, Moon and Venus. I checked it out , and it's true.(I mean for Venus wink.gif )
Now, if you look the figures, the magnitude of the ISS is way less than Venus' but, when you SEE the ISS, at least to my eyes, it looks, sometimes, way brighter than Venus.
Hence my question : does the ISS casts shadow?
I'll be hard to run the experience because,as Venus, the ISS is visible only after the Sun set or before the Sun rise which means you'll have to find the rigth day and be at the right place.
If somebody can prove ISS actualy casts shadow, it'll be a (fast) MOVING shadow. Sun, Moon and Venus can't do that. The only "celestrial bodies" that could cast moving shadows would be very bright meteroits, entering vehicules from space, ...
I've seen a mag -8 iridium flare cast a shadow. Not sure about the ISS though.

Yes of course it can cast a shadow. It is abundantly clear that some of the photons reflected from the ISS will impact upon your body and thus you will cast a shadow. Whether or not your eye could detect it is another matter.
QUOTE (paxdan @ Oct 27 2006, 01:39 AM) *
Yes of course it can cast a shadow. It is abundantly clear that some of the photons reflected from the ISS will impact upon your body and thus you will cast a shadow. Whether or not your eye could detect it is another matter.

Thanks! I must admit I was not expecting this kind of answer biggrin.gif. In France, when somebody ask somebody else : "Can you please tell me what time is it?", you've got an answer like xx Hours yy Minutes. In England you can be answered "Yes, I can" biggrin.gif wink.gif
Put in other words : I know now as much I knew before wink.gif biggrin.gif
I doubt a ISS shadow would be possible to detect without some very sophisticated equipment. But it can be with Venus:
Venus' max brightness is usually around mag -4.3. Anybody have a magnitude estimate for the ISS with the new panel array? If it's pretty close to this, then I think a shadow is a good possibility.

BTW, I used to frequently see a shadow from Venus even when it wasn't at max when I was a kid in Montana during the stands out pretty well on a snowfield.
Well - currently it gets to about -1 - I'm thinking -2 or -3 when it's finished.

Looking at Pete's efforts to image the shadow of Venus at a brighter figure than that, it's JUST visible....but over a 50+ second exposure, the ISS will cover 60 degrees of sky, so any shadow would have moved so much I really doubt it would be noticeable in imagery. Maybe someone will see it if their eyes are really dark adapted, but it'll be a tough call.

ISS moving rapidly might actually help the human eye to detect a shadow. The peripheral vision is best suited to detecting changes in light levels and subtly shifting shadows might be more easily detectable than faint stationary shadows. Still, magnitude -1 does seem a bit on the low side.
I just came across this interesting exercise to capture a shadow cast by Venus which reminded me of this thread. He has some good details on the technicalities of capturing this which do not bode well for any attempt to capture a shadow thrown by ISS - his Venus shadow's were captured from 4 minute exposures, F3.5 @ ISO 1600. Even if the ISS is as bright as -3 at a rough guess I think that a similar camera setup would require at least a 13 minute exposure during which time the ISS would cover around 50 deg.

The venus shadows are pretty cool though and I just love the target he chose to use.
Pete = Legend smile.gif Damn nice chap as well. Google for me + pete lawrence on Google and you'll see we go back about 6 years biggrin.gif

The venus shadows are pretty cool though -snip-

I have observed the shadow of Venus several times. Here in Palm Springs my neighborhood is dark enough to allow Venus at dawn to 'illuminate' the interior of my car port, where I can stand holding a white illustration board and observe it's shadows free of surrounding lighting. One neat trick to seeing them is to place the white board or paper sheet at your right peripheral vision fairly nearby with the left arm extended so that hands shadow will fall on the paper. One can see the shadow edge easier when you wiggle your fingers, allowing the changing shadow border to stand out better. Once this is readily seen, it is striking to see shadows of palm tree leaves from a block away also sharply outlined, due to the near point source illumination.
the brighter Iridium flares should also cast detectable shadows, at least for a few moments.

A full-up low-light real-time image intensifier system might do the job. Definately not something for long exposure low-light work.
Rob Pinnegar
Right. Next trick: capturing shadows cast by Uranus or Vesta. wink.gif
If the angle subtended by the ISS is less than the angle subtended by the sun (likely) then there will be no black shadow, but rather some lowering of intensity (partial eclipse). There are cool pictures of the ISS passing in front of the sun--it is relly small in comparison.
Floyd, the shadows being discussed are from sunlight reflected by the ISS back to Earth. Given that the ISS is heading for Venus-bright, it should be possible to see shadows these under ideal conditions.

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