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You'd see what?

  1. Apr 7, 2006 #1
    Suppose for a moment that there actually were regular scheduled flights going to and from the Moon. Not just one or two mind you, but a lot of them, and by a lot of them I mean thousands of them.

    Assume for the sake of argument that an elliptical trans-lunar orbit between Earth and the Moon had ships stacked in it, with five to ten miles distance maintained between each ship in that orbit.

    Assume that each ship had standard anti-collision lights, i.e. at minimum, a 2,000,000 candle power strobe mounted on it.

    Would you be able to see those ships from the ground?

    Would you see, essentially, that trans-lunar orbit the ships are in, as a spider web thin glittering line in the night sky?

    If you couldn't quite see it from the ground, would you see it from orbit where there would be no air to dissipate and absorb the light thrown off by the ships' anti-collision lights?
  2. jcsd
  3. Apr 7, 2006 #2


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    I'd think not. It is tough enough to see individual lights from low earth orbit, and that is only 150 miles away. The moon is about 220,000 miles away.

    It isn't a question of the atmosphere absorbing the light, it is the light spreading out with distance that makes it dim. Because of that, an omnidirectional light you could see from a thousand miles would pretty much blind you if you were within a mile or two of it.
  4. Apr 7, 2006 #3


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    If a candle is around 0.02 W, that's about 40,000 W. Compare this to the approximate reflected luminosity from the sun:

    [tex]L_{ship}=\frac{L_{sun}}{4\pi d_{earth}^2}(\pi R_{ship}^2)}f_r[/tex]

    If the ship is ~10 m in size and a perfect reflector (f_r ~ 1), this gives ~400,000 W. It's probably not a perfect reflector, so the luminosities might be comparable, but the reason we can see satellites in the sky is because of reflected sunlight, not onboard light sources.

    As russ said, the difference in distance would make it dimmer than geostationary satellites, but part of this would be made up by the presumably larger size of the ships. The brightness of an object shining by reflected light scales as the square of the size, as well as inverse square of the distance. I suspect they'd be visible in a small telescope.
    Last edited: Apr 7, 2006
  5. Apr 7, 2006 #4


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    Even thousands would only give 200 miles between them.

    I would really doubt they'd let ships get closer than that.

    (Not usre if you're looking for plausibility.)
  6. Apr 10, 2006 #5
    "Elephant's Bum Syndrome"

    actually I'm looking for dramatic vistas, things to ogle at in a fictional story I'm working on. But, frankly, at least imo, "looking for dramatic vistas" isn't an excuse for making things up whole cloth. Not that I think there's something inherently "wrong" with making up a Sci Fi setting for a story, just that it's not the ONLY way to do things.

    The bottom line is this - I'm tired of "artificial gravity plating", "force fields", "Battle of Britain" style space opera shoot 'em ups where space craft behave more like WWII fighters than objects subject to the laws of orbital mechanics, "photon torpedoes", "phasers", lasers, "warp drives", "FTL jump drives", "Galactic empires", aliens with two arms two legs and a head, killer robots, and the vast bulk of what in the last decade or so have become the "standard" story elements of SF written for a mainstream audience.

    This is essentially a "cops and robbers" story, and as such it's an ideal tale to use to get as far away as I can from "Star Wars" style SF, and back to something more akin to the tone and style of the second act of 2001.

    This question came about as I was trying to work my way through a long SFX pullback intended to establish early on, with a single shot, that "we're not in Kansas any more", but at the same time that "we're not suddenly in the Land of Oz" either.

    The idea was to pullback along a path from Tokyo into low Earth orbit on Earth's night side where you'd at first see a long string of blinking lights, that would soon be revealed to be the navigation lights of ships making their way into orbit, followed by a pan around that would reveal that between Earth and the Moon there was a staggering amount of traffic going into and out of orbit, to and from "space elevators", large commercial space stations, and major cities on Earth and the Moon.

    But the problem seems to be one of scale. Apparently it just wouldn't look like that. Even if there were a "staggering" amount of space traffic, you wouldn't really be able to see it.

    Even something the size of a "space elevator" wouldn't be all that noticeable from what I'm beginning to gather. At least not to the untrained eye. You might be able to see its counterweight from a few hundred miles off, but you wouldn't see the ribbons or the payload crawlers. By the time you were close enough to see details like that you'd be so close it'd be difficult to guess what you're looking at. It'd be like having your eye 2 inches from an elephant's bum. If you already knew what an elephant was, and what one looked like, it'd be easy to imagine the wider view, but if you didn't, it'd be tough to figure out what the hell you were looking at.

    All of which is fine. It was just an idea. I'll find some other way of making the point that isn't as susceptible to "Elephant's Bum Syndrome".

    Space Tiger & Russ;
    Oomph. Those numbers help put this idea in perspective for me. Tx. There's such a thing as "artistic license", but there's also such a thing as pegging the 'ol "Oh come on now" meter, too. What I'm shooting for here is "possible", not "possible only in your dreams". Seems this particular idea belongs under the second heading. I'll think of something else. Again, tx.
    Last edited: Apr 10, 2006
  7. Apr 10, 2006 #6


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    'nK, that's what I thought: wow factor, but plausible.
  8. May 2, 2006 #7
    I've seen satellites at night, because they reflect sunlight. One I saw was brighter than Mars, not as bright as Venus - quite spectacular. The sun had just set, so gave a good lighting angle to make a reflection to my eye. It slowly dimmed as it rotated. Must have been a large satellite. Large spacecraft would probably occasionally "flare" then dim as large flat areas turned to reflect sun toward the viewer. I read that a WWII pilot often spotted other fighters by the occasional sun reflection off the other plane's flat canopy glass.

    On spacecraft, 200 miles is closest distance allowed in geosynchronius orbit, probably closest allowed for current technology craft.

    Because of the failure of strobe lights (so effective on aircarft) at these distances, I expect spacecraft will use lasers that scan the sky (at least in the expected directions of other spacecraft) as navigational lights. These would be very visible. Lasers would also make good low-power communication beams, but might not use visible spectrum.

    A final comment on what you are tired of. Hollywood makes space travel look like a motorcycle chase. But I thought "2001 Space Odessy" was closest to truth - its more like a prison term!

    PS. If you need any thoughts, I have heaps of ideas about what it would be like living on the moon or Mars!
    Last edited: May 2, 2006
  9. May 2, 2006 #8


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    If it was brighter than Mars, it could only have been one of about three objects: MIR, the ISS, or an Iridium satellite flaring up. Iridium satellites are designed to flare as you suggested - if you know the date and time you saw it, there is a website around here somewhere that will confirm it.

    I saw the ISS a few months ago, I believe, pass very close to Mars in the mid-evening - you also may have seen that.
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