ATM analogy help - a little more about those boxcars

["Bell, Andrew" <AMB2@pge.com>]

Ed Hood's distance analogy is correct (a scale model of the universe at 1
inch to the AU would be just about the same as 1 mile to the light-year; for
metric units, can use 5 km to the parsec).  I like using this scale to do
things like place Epsilon Lyrae at a "distance" of a bit more than 150
miles, with the two pairs being separated by a bit less than a quarter of a
mile, while the separation between the components of each pair would be
about 10 feet.  It seems pretty neat that we can build telescopes that would
readily split the headlights on a big truck at distances of 150 miles and
more.

At this scale, even though the arms of the Milky Way are separated from each
other by thousands of miles, the Andromeda Galaxy would only be about ten
times as far away as the moon; the furthest galaxies that we usually look at
with amateur telescope telescopes are at roughly the same distance as the
earth from the sun, while the entire observable universe would be no more
than several times the size of the solar system.

Also at this scale - our own fairly ordinary-sized sun would measure about
one-hundredth of an inch (or a quarter of a millimeter, perhaps the size of
a grain of salt).  The hypothetical average star, which is a bit larger than
our sun, would be in the millimeter range and about the same size as a
coarse grain of sand.  So the "boxcar" model that Eric Uthus opened this
thread with would also be pretty close to 1 inch to the AU.  (To take this
just a little way back on-topic, the grits that we use for the first couple
of stages of a rough grind would be fairly representative of main sequence
stars at this size scale.)  Even the largest red giants should rarely be
much larger than a marble, and there wouldn't usually be too many of those
big red marbles in each wheelbarrow full of sand.

One more analogy and then I'll stop -- the billion boxcar train that I
described in my first posting would only be ten million kilometers long (at
ten meters to each car).  That's about how far the earth travels in its
orbit around the sun every four days, but you'd have to spread the sand from
those boxcars across the whole solar system and a bit beyond to match the
known distribution of stars and galaxies.  I'll leave it to the
professionals to figure out what to do with the dark matter!

-- Andrew Bell     

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Ed Hood wrote, in part:

Based on an AU being 1 inch, a light year is about 5,256'.
[And a mile is 5,280 feet][Volume 1 of Burnham is a good
reference for this observation.]