Your opinion please

I was chatting to a trainee teacher who had been tasked to give a lesson on
an astronomical topic. Her instructions were quite specific and the only
flexibility was in *how* she conducted the demonstration. She was told to
show how moving shadows of fixed objects proved that the earth rotated
around the sun. Props supplied consisted on polystyrene spheres of various
sizes. I have taken issue with this. Moving shadows demonstrate that the sun
is moving relative to the earth, but do *not* tell us what is moving. A sun
rotating around a stationary earth could also give the same effect.

I believe that it was Focault who supplied definitive proof that the earth
does, indeed, rotate whwn he performed his pendulum experiment. The shadow
observation is merely a demonstration of one of the effects of this
rotation.

Am I right?

Sally

Sally wrote:
The shadow observation is merely a demonstration of one of the effects
of this rotation.

Am I right?

You are exactly correct. The shadow observation was available to, e.g.
Galileo who, despite his assertions and some very clever arguments, was
unable to prove that Earth either rotates or that it orbits the Sun.

Foucault's pendulum is observable evidence of rotation and the
aberration of starlight is observable evidence that Earth moves relative
to the stars (& its changing direction is evidence of the shape of the
orbit).


Best,
Stephen

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Wasn't it Sally who wrote:
I was chatting to a trainee teacher who had been tasked to give a lesson on
an astronomical topic. Her instructions were quite specific and the only
flexibility was in *how* she conducted the demonstration. She was told to
show how moving shadows of fixed objects proved that the earth rotated
around the sun. Props supplied consisted on polystyrene spheres of various
sizes. I have taken issue with this. Moving shadows demonstrate that the sun
is moving relative to the earth, but do *not* tell us what is moving. A sun
rotating around a stationary earth could also give the same effect.

I believe that it was Focault who supplied definitive proof that the earth
does, indeed, rotate whwn he performed his pendulum experiment. The shadow
observation is merely a demonstration of one of the effects of this
rotation.

But isn't Foucault proving that the Earth rotates a completely different
result from proving that the Earth goes round the Sun? To prove that the
Earth goes round the Sun I think you have to also deduce that the stars
behind the Sun change through the seasons.

--
Mike Williams
Gentleman of Leisure

In message , Mike Williams
writes

But isn't Foucault proving that the Earth rotates a completely different
result from proving that the Earth goes round the Sun? To prove that the
Earth goes round the Sun I think you have to also deduce that the stars
behind the Sun change through the seasons.

Well, you can deduce that from the fact that the stars you see change
with the seasons but I'm not sure you have to deduce anything. The
observation that the stars change is very hard to explain any other way,
and if necessary you can observe the stars at a total eclipse.
--
Rabbit arithmetic - 1 plus 1 equals 10
Remove spam and invalid from address to reply.

"Mike Williams" wrote in message
news
But isn't Foucault proving that the Earth rotates a completely different
result from proving that the Earth goes round the Sun? To prove that the
Earth goes round the Sun I think you have to also deduce that the stars
behind the Sun change through the seasons.
Mike,
Yes, I am now a bit hazy about the exact point she was supposed to be
teaching, I think it was to prove that the earth rotates. I take the point
that other observations are needed to prove that the earth also orbits the
sun.
Sally

JRS: In article , seen in
news:uk.sci.astronomy, Mike Williams posted
at Sat, 10 Jan 2004 20:28:55 :-

But isn't Foucault proving that the Earth rotates a completely different
result from proving that the Earth goes round the Sun? To prove that the
Earth goes round the Sun I think you have to also deduce that the stars
behind the Sun change through the seasons.

Foucault, well measured and analysed, shows that the Earth rotates in
23h 56m with respect to the pendulum's preference. Observation shows
that the stars do likewise, and that the Sun's direction moves with
respect to them once per year.

It is then reasonable to assume that the pendulum's preference and the
stars are both fixed.

Kepler + Newton show that simple laws explain everything visible in the
Solar System, including comets; and those laws imply that a light Earth
moves round a heavy Sun (rather than vice versa), which does not need to
be otherwise fixed (i.e. is not nailed down).

Jovian satellite timings show the speed of light to be finite, and give
the sizes of the satellite orbits in light-seconds; which, given the
observed angular size of the orbits, gives the scale of the solar system
in light-seconds.

Aberration of the fixed stars proves nothing new, but shows consistency;
their annual parallax, where observable, gives their distance, in AU.

I forget what defined the AU in terms of yardsticks, but suspect that it
used parallax from different positions on the Earth.

The actual observations and deductions were not done in the ideal order.


Nothing absolutely proves that the whole Solar System (likewise
galaxies) is not actually an orrery using undetectable materials; but
the orrery is implausible and unnecessary.

--
© John Stockton, Surrey, UK. Turnpike v4.00 MIME. ©
Web URL:http://www.merlyn.demon.co.uk/ - FAQqish topics, acronyms & links;
some Astro stuff via astro.htm, gravity0.htm; quotes.htm; pascal.htm; &c, &c.
No Encoding. Quotes before replies. Snip well. Write clearly. Don't Mail News.

"Sally" wrote in message
...
Am I right?
Thanks everybody. I was a bit hazy about which rotation was in question...it
was the rotation of the earth. Looks like my friends educational mentors
need a little astronomy education :-)
Sally

"Sally" wrote in message
...
I was chatting to a trainee teacher who had been tasked to give a lesson
on
an astronomical topic.

It's good to know they have to learn a bit of astronomy. Many years ago, my
brother's physics teacher taught hime that sunsets would be blue if the
Earth rotated in the opposite sense.


DaveL

"Dave" wrote in message
...

"Sally" wrote in message
...
I was chatting to a trainee teacher who had been tasked to give a lesson
on
an astronomical topic.

It's good to know they have to learn a bit of astronomy. Many years ago,
my
brother's physics teacher taught hime that sunsets would be blue if the
Earth rotated in the opposite sense.


DaveL

*laughs* When I was a sprog, I asked a teacher whilst in infant school "What
keeps us on the Earth?".
"The Earth's spinning motion holds us to it." replies teacher.
Of course, mass and gravity are concepts that the teacher seemed to feel
were beyond us at that time. ;o)

"Wouldn't that fling us off though?"
I got glared at, then was asked to write the 12 times table on the board.

Cheers,
Subz