# If I have a giant structure from a satellite to another planet would the people below see it?

For this scenario Satellite means an object that orbits the planet, and my satellite is going to be a moon and the structure would be a giant tube going to another planet. What would the people on the planet see and why? Is there a way I could hide it if it was seen?

• Considering that people can easily see the ISS and other satellites with the naked eye, I'd say yes. (Depending on the distance.) If you don't want it to be seen, paint it black, and ensure that it doesn't pass in front of the illuminated part of the moon. – jamesqf Dec 22 '16 at 19:16

# How visible is your object

Assume the angular resolution of the human eye is 50 arc-seconds during the day.

The arctan of 50 arc-seconds is 0.0002424. Therefore, your structure is visible in daylight at a distance of $4.1 \cdot r \text{ km}$, where $r$ is the shortest diameter of your object in meters. A 100 m bridge would be visible in the air from 400 km away.

400 km, of course, would be the hypotenuse distance. Assuming your structure is perpendicular with the Earth's surface, the object would be seen to a height of 300 km in the air at 250 km away, etc. Any pair of numbers where the square root of the sum of their square is 400 is an acceptable vertical height-horizontal distance combo for visibility.

# What would it look like

Well...it would look like an object going up into the sky. Depending on the orientation of the viewer and the moon, the object would appear to either start at a point on earth, or if more than a few km away, start from a point beyond the horizon. It would then reach into the sky up towards the moon, but not reach it (unless the diameter is truly colossal). The object would get smaller with height until it became invisible at some height as calculated above.

# How to hide it

That isn't going to be easy, since I presume this object will be very large. If it is small (say, a 1 mm fishing line) then it won't be very visible at all. Making it translucent like a fishing line would help too.

Fishing lines are primarily seen by their reflection of light, not by the object itself. You would also want some sort of material property where it doesn't reflect or refract much light through it.

A combination of thin, translucent, and non-reflective will make your object hard to see.

It would likely depend on how wide and how far away the moon was. Depending on how close the moon was, the people could potentially see sunlight glittering off the tube (matt black paint could fix that) or a faint line in the sky (matt black paint as well).

The larger problem with this would be stopping the tube hitting the planet that the moon is orbiting around because if as you say the, the tube is going to another planet, when the moon orbits the first planet, the tube will hit into the first planet (no amount of matt black paint will hide it ;) ).

Hope this helped :)

• Welcome to the site Bob. Nice first answer. When you have a chance take a look at the help center and once you gain more rep feel free to join us in Worldbuilding Chat – James Dec 22 '16 at 15:28
• I do not understand why it would hit Iinto the planet, please explain. – Mendeleev Dec 26 '16 at 17:10
• @Mendeleev planets and moons are all in the same plane normally. if the moon is orbiting planet a, and connected to planet b, at some point planet a will be exactly between the moon and planet b. – Leliel Jan 16 '17 at 3:01