Astronomical
Distance megaConverter #39
INFORMATION
PAGE
Introduction and
Overview
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Units of astronomical measure are different
from common units and standards in that they
refer primarily to things not of this earth. The
size of outer space is so large that terrestrial
units are insignificant . There are really only
four units in wide use today, although as humans
continue exploring space there will probably be
more coined.
Humans are just beginning to explore space. As
we move away from earth the units coined here
will be less meaningful. No doubt new ones will
be made that describe physical features in
whatever new place we land. If the units are not
needed to describe some physical phenomenon ,
then we already have a built in system capable of
creating new units, called the metric system. 150
Gigameters is about an A.U. Ten Terameters is
approximately a light-year. A parsec is about 32
Terameters. A Petameter is about 31 parsecs. Many
other distance units can also be developed in the
same fashion.
See converters #2 & #26 & #27 for
standard conversions or ancient eras or foreign
countries. For a more comprehensive treatment of
measurements, find "NTCs Encyclopedia
of International Weights & Measures" by
William D. Johnstone at your local library. For a
better discussion of temperature, see any college
physics textbook.
* Much of our written history still refers to
things in common units. The Bible does not refer
to meters or kilograms, but to cubits and stadia,
or shekels and drachma. Wouldn't it be nice to
know what they were talking about way back then?
Now you can use megaConverter! For a more
complete listing of ancient, foreign, and
obsolete measures, download our
'megaSpreadsheet' of conversions in MS Excel
format.
Glossary
of Conversions:
light-year
The most common and useful is the
light-year. This is the distance a ray of light
will travel through vacuum in one standard earth
year.
light-second
This is closely related to a
light-year, and is the distance light will travel
through vacuum in one second.
Astronomical
Unit
Another unit commonly use is the
Astronomical Unit or AU. This is the average
distance from the earth to the sun. It is
commonly used in measuring things the size of
solar systems.
parsec
The last common unit of astronomical
measure is the parsec. This unit is important
because it was the basis of the method for
determining the distance from earth to the nearer
stars. Parallax is the feature of observation
that when viewing an object from varying
viewpoints, features in the background of the
object tend to move with respect to the object.
Hold your finger up in front of your face and
briefly close one eye and then the other. You
will note that objects in the background of your
finger will seem to shift position. This is
parallax. If you can determine the angle that the
background objects shift and you know the
distance between your eyes, you can calculate by
geometry the distance to your finger. Likewise,
if we use the earths orbital radius as the
distance between our "eyes" we can
measure much greater distances. Astronomers do
this with the earths orbit and use 1 A.U.
as the known distance. They then view the same
star three months apart and measure the change in
the background angle. A person can calculate that
a parallax of one second of angle with a baseline
length of 1 A.U. will yield a distance to the
observed object of about 3.26 light-years. This
distance is known as a parsec.
Note: Because of round-off
errors, converting from very large units to very
small units or vice-versa may not be accurate (or
practical). Conversion factors can be found by
converting a quantity of 1 unit to another unit
several steps above or below the first. You may
need to string several conversion factors
together to find the factor from a very large
unit to a very small unit, and then you can use a
calculator with sufficient digits to find your
answer.
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