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View Full Version : Visibility of space-stations from Earth???



Githyanki
2013-Dec-19, 05:07 AM
What would 2001-like ring-stations and ONeil-size space-stations look like from low-Earth obit, geostation and L1-5 points look like from the surface of Earth?

antoniseb
2013-Dec-19, 12:30 PM
At the L4 and L5 points they would be invisible to the human eye (too distant). L3 would be behind the Sun.
As to the others, I'd have to think about it a bit. The LEO positions would be very bright, but you probably don't want an O'Neill sized station where its orbit would eventually decay and take out a huge swath of inhabited territory.

chornedsnorkack
2013-Dec-19, 01:01 PM
At the L4 and L5 points they would be invisible to the human eye (too distant). L3 would be behind the Sun.

No, it would only be in front of Sun during some lunar eclipses.

Suppose a natural satellite were as black as Moon and at Kordylewsky clouds.
Then it would be 10 magnitudes dimmer than full Moon if it were 100 times smaller - at 35 km diametre it would be a point 18 seconds across, and -2,7 when it is full and Moon is gibbous. It could still be visible to naked eye as inconspicuous but moving body if it were another 8 magnitudes dimmer at +5,3... in which case it would be 900 m diametre.
That assuming it is black as Moon (geometric albedo 1). If it were white, it could be even smaller.

Jeff Root
2013-Dec-19, 02:32 PM
The Lagrange points referred to are in the Moon's orbit around
Earth, not in Earth's orbit around the Sun. O'Neill habitats are
big enough to be visible in the L4 and L5 positions, but I don't
know offhand if they would be extended objects or pointlike
to the naked eye.

The space station in 2001: A Space Odyssey was in an orbit
about a thousand kilometres up. Apparently they didn't quite
grok the seriousness of the Van Allen radiation belts. At that
altitude, I'm not sure whether it would be an obvious circle
to the naked eye (given the required lighting). Maybe for a
kid with good eyesight. I'd kind of expect it to always be
edge-on to Earth, but that might not be true at all. It might
even maintain constant orientation relative to the Sun, like
O'Neill habitats would.

-- Jeff, in Minneapolis

antoniseb
2013-Dec-19, 03:24 PM
The Lagrange points referred to are in the Moon's orbit around
Earth, not in Earth's orbit around the Sun. ...
Yes, I see you are right, and I had misremembered L5 Society details.

L2 is behind the Moon. But there were only supposed to be ONeill Habitats at L4 & L5, so the L1, L2, & L3 questions are purely academic.
There was never any specific plan for the O'Neill habitats, just general suggestions for size. If they were 2km radius and 10km long, and painted white, what stellar magnitude would they be at 240,000 miles? I guess it would be near the limit of what the eye can see.

chornedsnorkack
2013-Dec-19, 03:50 PM
If they were 2km radius and 10km long, and painted white, what stellar magnitude would they be at 240,000 miles? I guess it would be near the limit of what the eye can see.

You have my calculations two posts back. If painted white, they would be near the limit of what eye can see if they were 100 m radius and 400 m long.

Githyanki
2013-Dec-25, 02:28 AM
Are there any accurate CGIs of them from Earth?

Just in Oblivion, the Tet seemed to be in LEO and appear white like a cloud; just sure if that's accurate...

Glom
2013-Dec-25, 02:21 PM
Are there any accurate CGIs of them from Earth?

Just in Oblivion, the Tet seemed to be in LEO and appear white like a cloud; just sure if that's accurate...

That visual was cool. Also, the Elysium in the so-titled movie.