Science Talk

Raymond C. Glassford · Guest

I am still wondering why telescopic photos of Mars from Earth show green
areas that expand and contract with passage of the martian seasons, yet
photos taken by spacecraft orbiting Mars do not show green areas. This
question has puzzled me ever since the first photo fly-by of the planet
by Mariner 4. Now, many years have passed, computers and the Internet
have arrived, and searching with Google is not able to provide me with a
plausible answer ... at least not so far.

Can someone summarize, or point me to, the currently held "majority
view" that explains this discrepancy?

David Williams · Guest

-> Not knowing which pictures you mean, I can only guess.
-> Chances are, the pic was 'false-colour', showing something that changes with
-> time...
-> maybe temperature?

Back about 100 years ago, some observers did think they saw seasonal
expansion and contraction of green areas along the Martian "canals". It
was hypothesized that the canals carried water that irrigated nearby
land and allowed plants to grow. Later, some people thought the colour
was not green but purple, so it was supposed that Martian plants have a
purple type of chlorophyll, as do some kinds of seaweed on Earth.

Nobody ever succeeded in photographing these colour changes. Nowadays,
they are considered to have been visual illusions, like the canals
themselves.

dow

Raymond C. Glassford · Guest

David Williams wrote:

BradGuth · Guest

On Jun 21, 6:32 pm, david.willi...@bayman.org (David Williams) wrote:

David Williams · Guest

-> Forgive my age-induced ignorance of this topic. My thinking on
-> scientific studies of Mars was unduly influenced by earth-based
-> telescopic observations of the planet conducted during the early to
-> mid-twentieth century. Reading "Mars and Its Canals", by Percival Lowell
-> (1907), during my teen-aged years certainly was not a contribution to
-> "good" scientific knowledge, although the book was a good read.

I agree. I did most of my early astronomical reading, in the 1940s and
50s, from books that my father had acquired some 25 years earlier. New
books were hard to get when I was a kid in post-WW2 Britain. My dad's
books were full of exquisite sketches of Mars and other planets, done
by astronomers who had spent hours gazing through telescopes hoping for
occasional moments of "good seeing", when details would be visible.
Needless to say, their imaginations had provided most of the details.

The solar system was a very different place back then. Not only did
Mars have vegetation and maybe civilization, Venus had oceans and
presumably life. Mercury had one fiery-hot side, and another side that
never saw the sun and was probably the coldest place in the solar
system. Saturn, of course, was the only planet with rings.
Newly-discovered Pluto was about as massive as Neptune or Uranus, and
its apparent small size was a mystery. One theory was that its surface
was smooth and shiny, so we could see only the tiny reflection of the
sun.

"Knowledge" has changed...

dow

Ron Miller · Guest

On Jun 20, 6:59 pm, "Raymond C. Glassford" <rcglassf...@copper.net>
wrote: