On Thu, 01 Sep 2005 11:41:07 -0500, Tom Roberts wrote:

Pentcho Valev wrote:

[ some of Pentcho's garbage snipped, along with Tom's reasonable
responses ]

The observer can measure, for instance, the frequency shift and, if
Einstein is right, a non-zero frequency shift corresponding to the
changing velocity of light will be detected.

Hmmm. For the case of observing stars' images before, during, and
after an eclipse, the change in frequency is higher order in
(extremely) small quantities than the deflection. I'm pretty sure it
is well below realistic experimental resolutions.

If the Sun is stationary relative to us (bad assumption but let's make
it anyway) then shouldn't there be _no_ frequency shift induced in the
light as a result of its passing near the Sun? (Assume the Moon is
massless or else so light we can ignore it -- "Styrofoam Moon".)

After all, a particular number of wave crests went into the Sun's gravity
well, the same number came out, and whether the light went near the Sun or
not makes no difference to how many seconds of time our clocks tick off.
So, there can't be any redshift/blueshift from that cause, _if_ the Sun
is stationary relative to us. (I stated that rather loosely; I hope it's
clear what I meant.)

On the other hand, if the Sun is moving transverse to our line of
sight, then ... uh ... wouldn't the light "steal" a little energy from
the Sun if it passes by the backside, and wouldn't it "give up" a
little energy if it passes by the front side, with the Sun being slowed
or accelerated slightly as a result? That would imply that stars on the
edge of the sun which is "in front of" our orbital path around the Sun
should be slightly blueshifted, and light which is "in back of" our
orbital path should be slightly redshifted, as a result of its trek close
to the Sun.

Right...?

Viewed differently, on the backside, the 3-d path is "getting shorter" as
the Sun moves out of the way, so the number of wavecrests "in transit"
must be decreasing, which implies there's a blueshift. On the front side,
the path is "getting longer" as the Sun moves into our line of sight, so
the number of wavecrests "in transit" along that line is increasing, and
there must be redshift. Rather pleasingly, both these rather fuzzy mental
models arrive at the same conclusion -- maybe it's even correct...


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