Re: Newbie Needs GPS Selection Advice

From: Peter (prathman_at_comcast.net)
Date: 09/22/04 

Date: Tue, 21 Sep 2004 17:12:02 -0700

Gymmy Bob wrote:

> Let me make an analogy to clarify this non-exageration: If you look up into
> the sky at night between any stars or other heavenly bodies...how far can
> you see?

Billions of light-years. Now if I want to actually get some details of
what I'm looking at I'll check out the Hubble "Deep Sky Field" which did
what you specify, i.e. picked a piece of sky without any nearby objects.

Here's what was there:
http://store3.yimg.com/I/skyimage_1796_2423909

But of course when looking at the sky I judge how far I can see by what
I can observe rather than by what I can't. So on a clear night I
observe that I can see planets out to 10s of astronomical units,
bright stars out to hundreds of light-years, large galaxies out to a
few million light-years. So looking at an apparently blank piece of sky
tells me that none of those types of objects out to their respective
distances are present in that direction. But if all the visible objects
disappeared then I'd have no good way of judging what I could see at
what distance.

Similarly, if I'm in fog so dense that I can't see past
the hood of my car, then I have no data to go on as to what
obstacles might be out there beyond that distance. And even
if I'm able to dimly make out a headlight, it doesn't
give me any assurance that there might not be a pedestrian
or other unlit obstacle in my path.

Such dense fog doesn't last long and is not life-threatening.
Trying to drive through it is illegal, unsafe, and ill-advised
with or without a GPS.

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