Quote of the Day - 15 July 2005

A low orbit for the Space Shuttle is 300 km above the surface. The biosphere is 10 km or so. Sorry, Dr. Wilson. The spirit of what you say is true, but the letter is not: the biosphere can be seen edgewise from a space shuttle.

I wouldn't doubt that the astronauts can see a 10 kilometer high terrain feature, but I would doubt that they can see any indications of the biosphere ON that terrain feature. At those distances, the biosphere coats the corrugations of the terrain like a thin film.

That being said, I understand that certain features of the biosphere CAN be visualized, particularly man-made ones--flares from gas wells at night, city illumination at night, lakes backed up by linear features that must be dams, the green color of jungle, forests, and fields, large planktonic discolorations in the ocean, etc.

But most of these aren't usually visualized from an edge-on perspective, so...

re: orbit of shuttle

The number Mr. Hopkins quotes forgets to account for the radius of the earth. So the correct comparison is just under 6700km to 10km. Simple trig puts that in the neighborhood of 1/12 of a degree, assuming this calculator works properly. IIRC, puts it at the edge of human acuity, but visible at that orbit. After checking, someone with 20/30 vision would just be able to discern the biosphere edge-on at low earth orbit.

Oops, my math was off a bit (didn't draw my diagram correctly). The tangential distance at that orbit is a bit under 2200km. So a 10km biosphere would be closer to 1/4 of a degree at that orbit. Definitely visible, even to someone with 20/200 vision.

Facts are meaningless. You could use facts to prove anything that's even remotely true!

I wouldn't doubt that the astronauts can see a 10 kilometer high terrain feature, but I would doubt that they can see any indications of the biosphere ON that terrain feature. At those distances, the biosphere coats the corrugations of the terrain like a thin film. That being said, I understand that certain features of the biosphere CAN be visualized, particularly man-made ones--flares from gas wells at night, city illumination at night, lakes backed up by linear features that must be dams, the green color of jungle, forests, and fields, large planktonic discolorations in the ocean, etc.

Oh, yeah, Lenny, I agree (agreed?), I think, that you can see a lot from shuttle orbit, in the Nat. Geo. cover shot, two-dimensional pizza-toppings spread on the earth's platter, sense.

But I think the concept we were playing with was the visibility of the "thickness" of the biosphere--

"a membrane of organisms wrapped around the earth so thin that it cannot be seen edgewise from a space shuttle"

--so we're not talking (at least as I interpreted this image) about the two-dimensional or horizontal "spread" of the biosphere, but rather of the biosphere's third or vertical extension.

The suggestion was then made that the biosphere was 10 km "thick" (vertical measurement, from top to bottom). Assuming we're only talking about what's visible (and not about the ocean's depths or whatever microfauna may dwell deep below the crust of the earth), I took that poster to be referring to the depth or height of the surface terrain features over which the biosphere is spread. I took mild exception to that estimate, because while the surface terrain may vary by that much, the biosphere itself is spread rather thinly over that terrain.

So the question then became, in my pointy little brain, how "thick" is the biosphere "above" any particular chunk of terrain, irrespective of the height of the terrain feature itself?

There's room for debate, depending on definition (and, unlike some of the other debates going on the other threads, this one is just for fun, I hope)--you could include everything from sea level to the heights reached by the geese that migrate over the Himalayas. You could include the rarer, higher visitations of lifeforms, like U2 overflights, the recent "edge of space" flights, heck, the space shuttle and space station themselves.

But in terms of a "visible" biosphere, it makes more sense to me to think in terms of tall trees, maybe skyscrapers. You're not going to see birds, bats, or butterflies in mid-flight from LEO. Even if you throw those in, the typical flight-height above the nearest terrain is NOT going to be the height of the Himalayas, but the few hundred feet by which the geese CLEAR the Himalayas.

So I would argue that the "height" of the biosphere is a few hundred feet. That few hundred feet arguably is NOT going to be visible "edgewise" from LEO, though the height of the terrain on which that thin living membrane is spread might be.

All of which brings us to "edge-on." I think I agree with a corollary of one of your points here--the shuttle can NEVER really get an "edge on" view: it's always going to be suspended over mid-platter, and one have no way to acquire good visualization of the "thickness" of the biosphere (however we define that and whatever number of meters or kilometers we assign) because that view is only visible at the very horizon line, or as the soap opera would have it, As the Biosphere Turns.

re: orbit of shuttle The number Mr. Hopkins quotes forgets to account for the radius of the earth. So the correct comparison is just under 6700km to 10km. Simple trig puts that in the neighborhood of 1/12 of a degree, assuming this calculator works properly. IIRC, puts it at the edge of human acuity, but visible at that orbit. After checking, someone with 20/30 vision would just be able to discern the biosphere edge-on at low earth orbit.

— W. Kevin Vicklund

Mr. Vicklung forget to account that the radius of the Earth is irrelevent. Indeed it is NEVER relevant to the calculation. The biosphere is part of the observable universe as well, but he did not cite it for some reason. We don't care about the entire earth for the same reason we don't care (for the purposes of this calculation) what the size of the universe is. The angle in question comes ONLY from the width of the item being observed (10 km) and how far away the observer is (300 km). That is easily visible.

Bear in mind, 300 km is the height of the shuttle above the ground directly below it. For a meaningful calculation of how thick the biosphere would look at the horizon (for an "edge on" view), you have use the distance of the shuttle from its horizon. And for that, you do need to take the radius of Earth into account.

— Walter Brameld IV