home
***
CD-ROM
|
disk
|
FTP
|
other
***
search
/
Floppyshop 2
/
Floppyshop - 2.zip
/
Floppyshop - 2.iso
/
diskmags
/
4671-5.790
/
dmg-4961
/
power
/
space.pwr
< prev
next >
Wrap
Text File
|
1989-12-31
|
2KB
|
41 lines
WHAT ON EARTH CAN YOU SEE FROM SPACE ?
**************************************
BY KARIAKI
**********
When men first flew in space,they were amazed to discover that
the only man made object visible from orbit was the Great Wall of
China-or so advertising copywriters would have us believe.It's a nice
idea,but it's not true. None of the early astronauts mentioned
sighting the Great Wall.Various other man-made phenomena such as the
fires of African desert dwellers,the lights of tuna-fishing boats off
Japan,or the giant irrigation patterns in the American North-West are
visible from low Earth orbit (about 200 kilometres up)with the naked
eye.
Theoretically,the human eye is capable of a resolution of
less than one minute of arc-so,good eyes should be able to see objects
about 0.3mm across at a metre distance.At 200 kilometres,the same eyes
could pick out objects about 50 metres wide.Such high
resolution,though,depends on the contrast between object and
background being good- a black thread against white,for example,or a
white concrete runway against a brown terrain.The Great Wall is mostly
grey stone in a grey landscape-and in fact,is difficult to pick out
even from an airliner flying a mere 15 kilometres above.Shadows cast
by the wall in low sunlight may show.
There are at least two man-made objects you can
certainly can see from space.First,the accelerator ring at
Fermilab,Chicago,which is six kilomteres in diameter,has a road
running above it and is marked by ponds and woodland.And the second,a
wire fence in Western Australia marked by a massive contrast between
grazed farmland on one side and desert on the other.