SETI again

On 7/20/06, Robert wrote:
(...)
> ok some believed it, but just look at how much trouble Columbus had
> in conviencing anyone in the 1400's that the world was round.

Although popular belief holds that (perhaps due to that Bugs Bunny
cartoon were a comical Columbus is portrayed trying to convince the
Spanish king), Earth sphericity was not the problem in Columbus
theories.

The problem was that Columbus used calculations from an ancient
Phoenician from the 1st century before Christ, Marinus of Tyre, which
postulated that landmasses occupied two-thirds of Earth circumference,
and also misconverted measurements of Earth circumference from the
writings of a Persian astronomer from the 9th Century AD, Al-Farghani.
As a result, the Earth imagined by Columbus was 25,000 Km in
circumference, almost half of the actual size of Earth (more
Mars-sized than Earth sized) and mostly covered by land instead of
oceans. However, most of the geographers and astronomers of the time
agreed upon a circumference close to the real value of 40,000 Km and
(taking apart fictional works like the Divine Comedy) assumed that
there was nothing else but water in the rest of the world. In such a
situation, trying to cross an ocean that big seemed a temerity, and it
was simply natural to find that Columbus was a lunatic sloppy with his
calculations - and yes, that was precisely what he was ;-).

In fact, even the Spanish crown probably saw Columbus as a demented
navigator, but they were hopeful that he would find some unknown
islands during his folly. (After all, the Portuguese had discovered
many new islands in the 15th Century.) It turns out that they were
lucky and Columbus found another group of continents. (Even though he
died thinking that the Americas were in fact Asia.)

> everyone still said you fell off the earth if you went to far away
> from land.
(...)

Actually, the prevalent theory of gravity (again developed by ancient
Greeks, and in parallel by ancient Hindus) among educated people at
the time said that objects have a tendency to fall towards the ground.
if Earth is spherical, then the ground is also curved and what is "up"
in some point of Earth maybe "down" from some other point. An example
of this notion among educated people is in the aforementioned Dante's
Divine Comedy. In the book Dante travels through the center of Earth
(yes, Jules Verne was not that innovative ;-) and emerges in the
antipode, in the then-unknown Southern Hemisphere, were he finds the
Purgatory, which was an island inhabited by the ghosts of the
recently deceased. However, the Purgatory is not described as "upside
down" and the ocean stays were it should be, over the ground (or,
saying better, over the ocean floor). As a side note, Dante probably
imagined the shortcut through the center of the Earth because Saint
Augustine wrote in the 4th or 5th century that it would be
"impossible" to cross any vastness of sea that separated the known
lands from any hypothetical unknown land that might exist in the
Antipodes.