Re: Directional Coordinates
From: Chris L Peterson (clp_at_alumni.caltech.edu)
Date: 12/10/04
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Date: Fri, 10 Dec 2004 16:49:24 GMT
On 10 Dec 2004 07:47:45 -0800, "Chuck" <Vancgrywlf@AOL.com> wrote:
>I have read about the complex system that the astronomy
>community uses, which is necessary to figure directional reference in
>the universe. Like others, I have a very general idea of how it works,
>but still lack much in the way of being able to think of it in a
>practical manner.
>
>It would seem that in some way a method could be devised so that any of
>these coordinates might be better visualized. For us laymen, one of
>many confusing things about the universe is there is no up or down --
>north, east, south or west.
The system is not at all complex. It is precisely the system we use on Earth,
latitude and longitude (for astronomical coordinates, latitude is called
declination, and longitude is called right ascension). And just like the
terrestrial coordinate system, there are fixed directions north, south, east,
and west.
There is a slight complication that the Earth rotates, which means that the
position of a given astronomical coordinate changes with time, but it is simple
enough to run a planetarium program to see what the sky looks like at any
particular time. The object coordinates don't change with time, so a star chart
is fixed.
>Knowing where the HST is located in relation to the earth at the time a
>particular image is taken along with the direction the telescope is
>aimed, would be very interesting for me.
There is no need to know the exact position of the HST when a picture is made,
only the direction it is pointed. That's because everything it is aimed at is so
far away that the range of positions it can be in make no difference to the
image. And the direction of every image is available as a coordinate pair, right
ascension and declination.
>I've often thought that 3 dimensional software models might be designed
>with the ability to show the actual aim trajectory and in some cases,
>even the target of most telescopes. I'd think that this software could
>be designed, so that by entering the HST and any earth based telescope
>coordinates into the software program, you'd have the desired results
>for that particular day.
>From a practical standpoint, astronomers (and the HST) essentially live in a
two-dimensional environment. With the exception of our own solar system,
virtually every other object can usually be treated as existing on the inside of
a sphere whose surface is infinitely distant.
>Needless to say, a 3D model of the Solar System in combination with the
>Milky Way Galaxy, the Local Group and so on would certainly help to
>better envision the BIG picture of at least a very small part of the
>universe.
Such programs exist. They allow you to simulate space travel, and watch how the
relative positions of things change as you travel cosmic distances.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
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