How large does a space station have to be to be visible on the day?

[Elthy]

Maybe someone calculated this allready....

With visible im not talking about a spot of light, it should be visible as a structure. Kinda like the moon is often visible in daylight...

[Evanitis]

It won't happen in stock, the vanilla render distance is 2.5k. But there is a Distant Object Enhancment mod. I have no clue how big you need to build for it to be more than a dot though. Or if that will ever happen. 70km is pretty far away.

Edited January 12, 2016 by Evanitis

[Elthy]

Im not talking about KSP, but real life...

[vitekc45c]

About "thats no moon" size.

[Temstar]

Depends on orbit and albedo. Sputnik was tiny but it had a low orbit and a very shinny shell so it was quite visible to the naked eye despite its size.

[RainDreamer]

Well, as big as buildings that can be seen 400-500km away on the surface? Mountain size, probably

[Thiagobs]

It depends on several factors, like distance from the observer and angular distance (how "big" the structure is perceived to be)...

For a structure orbiting as high as the ISS (altitude of 400km / 249 miles) to be perceived as the same size as the moon (angular diameter of roughly 0.50 degrees), it would have to be about 3500 meters / 11500 feet wide

[Elthy]

Wow, thats quite small and totaly possible with e.g. large solar panels...

[NovaSilisko]

11 hours ago, Temstar said:

Depends on orbit and albedo. Sputnik was tiny but it had a low orbit and a very shinny shell so it was quite visible to the naked eye despite its size.

Sputnik wasn't nearly as visible as the booster that carried it. They painted the rocket core white so it would catch the light more easily. When looking for Sputnik, most people would see the rocket stage - not the much dimmer point nearby that was Sputnik itself. Also visible were the two fairing panels that ejected just before Sputnik did. So, technically, the order of objects in orbit is: Rocket stage->fairing panels->Sputnik

 

For visible diameter, I refer you to this handy chart:

 

So for perfect vision, with the ISS directly overhead with its solar panels aiming at you, it's just small enough to not be discernible in shape. Something four times the size of ISS, though, and you'd start to be able to make out its geometry (assuming excellent vision again). The ISS is in fact visible in daylight early or late in the day (source: I saw it), but only barely. It's very easily lost in the bright sky.

Edited January 12, 2016 by NovaSilisko

[Gaarst]

To be distinguishable by the human eye, that station should be... a few meters larger than the ISS, at least 115m more precisely.

You get this result using the angular resolution of the human eye (about 1 arcminute), and basic trigonometry; in the end, if the station orbited the Earth at 400km, and was bigger than 115m, then you could properly "see" it when it passes the zenith.

Note that this is the theoretical minimum: other factors, especially brightness and the atmosphere, would probably make the station invisible to the naked eye.

[WinkAllKerb'']

iss visible in the sky ... definitely usefull related to obscurantism @ some point ... it start gettin borin'

just "slighty" borin'

Edited January 12, 2016 by WinkAllKerb''

[Wjolcz]

Just in case someone wants to know when and where in the sky the ISS and Irridium flares appear: Go grab the ISS Detector from the app store if you have Android.

I already got three of my friends interested in "The Space Stuff" because I showed them that.

[lajoswinkler]

A station might be enormous, but still invisible as it simply isn't bright enough to be discernible in the bright blue sky, unless it flashes the sunlight directly at us like Iridiums do.

[Elthy]

I doubt that would be a problem, isnt the moon realy dark, too?

[WinkAllKerb'']

make it the same shape of some specifics located caracters/ideopictogramm/languages in the sky. like hello "usa" or whatever xDr

so much irony xDr my bad xDr giggles translat' & a /SpockSalutePalm:

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

+

Edited January 13, 2016 by WinkAllKerb''

[lajoswinkler]

4 hours ago, Elthy said:

I doubt that would be a problem, isnt the moon realy dark, too?

Apparent magnitude of the Moon is -12.74. Even if you chopped it to tiny bits, magnitudes are still using a logarithmic scale... I can't be sure, but I'm inclined to think it would be invisible unless directly reflecting the Sun.

[cantab]

So it looks like a couple of hundred metres and it starts to be Not A Dot to people with good eyes. But you need more like a kilometre for someone on the ground to be able to clearly make out the general shape.