ISS Visibility in Daylight

[MeteorWayne]

The ISS is now so bright it can be seen after sunrise and before sunset. While it is unlikely to be sighted when the sun is high in the sky, for at least an hour or more of the daylight hours it should ve visible on a high pass, based on last night's observation. I dragged the astronomy class I am teaching outside about 5 minutes before sunset for a "neckbreaker" near overhead pass, and we had no trouble at all spotting it.

Heavens-Above now lists daytime passes (in a separate section), so give some a try! It is of course easiest for a directly overhead pass (also that's when it's brightest), but only some testing can detrmine how far the envelope can be stretched.

http://heavens-above.com/ (Don't forget to set your location and save it)

 

[aphh]

It's getting there. We can see the moon and it's phases when the sky is already blue, so it means ISS is almost there aswell.

Ofcourse the intensity of ISS is concentrated on much smaller area in square degrees or steradians than, say, half moon, but still it has to be getting close to the point you could spot the ISS when sky is already blue.

Not for me, though, as ISS for me is one thousand kilometers away at best when for you it's only about 350 kilometers away at best.

 

[MeteorWayne]

That's what I said in the first post. It was easily visible when the sky was blue before sunset.

 

[Fomalhautian]

Heavens-Above now lists daytime passes (in a separate section), so give some a try!

Very cool. Thanks.

I haven't been to that site in a while...... I see you can track the ISS Toolbag as well. :lol:

 

[aphh]

That's what I said in the first post. It was easily visible when the sky was blue before sunset.

What about the magnitude of such pass? Is it based only on the intensity of reflected sunlight, in which case the magnitude would always be the same regardless of the luminosity of the background. Or is the magnitude relative to the brightness of the background?

 

[MeteorWayne]

The magnitude depends only on the reflected sunlight, the background doesn't affect that.
They don't give the magnitude on the daytime/all passes page, but if you look at the nighttime passes you can get a good feel for what they are for a given altitude. It's between -2.5 and -3 for an overhead pass.