Re: Re: [FH] FTL, astronomy

----- Original Message -----
From: "B Lin" <lin@rxkinetix.com>

> Spectra are unique, they are formed by different amounts of various
elements that produce more of one color when burned.  A problem arises
when
dust, hydrogen or nebula are in the way as they might absorb parts of
the
spectra, reducing the usable parts and making ID more difficult.
>
> You would determine range to a star the same way astronomers currently
do.
How do you think they know Alpha Centauri is 4.3 light years away?
>
> --Binhan

Range determination to any single star is not very precise and unlikely
to
be precise enough for navigation even in the future. The most precise
distance determination are obtained by parallax measurement: measure the
direction to a star, wait till Earth is on the oter side of the sun,
measure
the direction again, do a little trigonometry and you can calculate the
distance. Pretty impractical for a spaceship.

Also not that determining just the distance to a single object does not
give
you your position. You just know you are on the surface of a sphere with
a
radius of 4.3 light years. You need the distance to three objects. As
range
measurement is imprecies, measuring the angles and triangulating give
you a
much better position. You must know the distance between those objects,
but
not your own distance from them.

Which may well be the major limit to accuracy in deep-space navigation.
How
well can we know the 3d-positions of our space beacons ?

Greetings
Karl Heinz