Margo Schulter wrote:
In sci.astro Paul Schlyter wrote:
In article . com,
Jeff Root wrote:

http://www.bautforum.com/showthread.php?t=34542

The questions I asked:

Were the Sun and Moon commonly referred to as "planets" in
ancient times?

When was Earth first called a "planet", or described as a body
comparable to a planet, even if it wasn't thought to wander?

When were the stars first recognized as being like the Sun?

Probably around Copernicus' time. One prevailing argument against
a heliocentric solar system was that the Earth's orbital motion
around the Sun ought to cause a quite visible yearly parallax
among the stars --- unless of course the stars were extremely
distant and not just a little farther away than Saturn, as was
commonly believed in that time.

"Show us the stellar parallax" was also one of the lines of
rebuttal to Galileo -- since if one followed the view expressed
by St. Roberto Bellarmino (1615) that the traditional geocentric
interpretation of certain Bible passages should be altered only
on the basis of indubitable proof, the "missing" parallax could
still be a reason for doubt. As I recall, the Church gradually
grew more and more reconciled to Galileo's perspective as the
18th century progressed, but didn't make it fully "official"
until the early 19th century, when parallax was confirmed for
one or more of the nearest stars to our Sun.

When the stars did turn out to be that vastly distant, they
must also be very bright --- like the Sun.

Herschel was one of the first trying to find the actual distance
to some stars, and he thought Sirius was some 3 light years away.

Interesting! Maybe that's about the same degree of accuracy as
Roemer's estimate of the speed of light (1676) using the moons of
Jupiter. It was an awesome leap -- I'm trying to find a worthy
adjective -- from the state of things earlier in the century,
when Galileo had tried the experiment of having two people a few
miles away show lamps to each other and try to estimate any delay
in seeing them at that distance.

I found two speeds for Roemer's expeirment depending on the distance of
an AU. Initially the time for light to travel an AU was thought to be
11 minutes, which is 11/8 or 1.375 of its actual time. Which is clearly
beyond 8.6 LYs.

However, by using Roemer's estimate of an AU (See:
http://en.wikipedia.org/wiki/Ole_R%C3%B8mer), the speed is 135,000 km
per second compared to the roughly 300,000 km per second it is. So,
Sirius at 8.6 LY, we get 135/300 = .45 * 8.6 = 3.87 LY, so Roemer and
Herschel (using 3 LY) were not that far off.

Eric