Re: Star Distances
- From: Saul Levy <saullevy1@xxxxxxx>
- Date: Fri, 23 Jun 2006 10:58:18 -0700
Yes, many years of plates are taken to increase the accuracy. Today
parallaxes are often measured electronically, no photographs are
taken.
Since only relatively nearby stars can be measured by the parallax
method, most field stars will be much farther away and perfectly
suited to be reference stars. If by chance you happen upon a
reference star which is much closer, it will leave it's mark by also
showing some parallax. It cannot hide in the data.
I used to work for Nicholas Emory Wagman at Allegheny Observatory. He
was truly a genius at arithmetic and could find any errors either
caused by a reference star having parallax/proper motion or a
calculation error by the measurers (including me!). He always told us
to recalculate any errors we made. Usually the final parallax was
derived by Dr. Wagman, but one time he let me do the entire
calculations. It was quite interesting even though I missed a lot of
exactly what the technique included. Many sources of error are
corrected for and technique errors avoided.
I also measured tau Ceti which is a nearby star with a large proper
motion. The p.m. has to be corrected for at regular intervals so that
it doesn't affect the final parallax. That was a lot more work, but
is common in parallax work.
Saul Levy
On 23 Jun 2006 08:46:47 -0700, "Hurt" <hurt_beyond_repair@xxxxxxxxx>
wrote:
.Suppose I put a mark down at one end of a field, then another
mark at the other end, and then I take a tape and measure
the difference between them. Yes, I've done two "snapshots".
But would you describe that as "measuring two lengths"?
These are not exactly analogous situations. You're not measuring two
lengths but you are taking two data points, the first being zero, the
beginning of the tape measure. In this case though you have
definitively set both your reference and target points. In stellar
measurements all points are to some degree a moving target. Initially
both the reference star and the relative motion of the target star are
indeterminant; two unknowns requiring a minimum of two measurements.
Uh, no. The point is that there is a star (a distant one) that the
near star IS shifted relative to. You only require two stars, one
near, one far. And all you care about the far one is that it IS
far.
That's theory, in actuality astronomers have to take many photographic
plates to find a reference star that isn't shifting relative to the
target star. Initially we don't know how far any of the stars are.
You're either being prick or just ignorant if you dispute this. I
think it's both personally. Go talk to an astronomer and/or therapist.
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