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Figure one. Diagram showing the overlapping scales used to
measure the Universe.
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The cited modern distances to celestial objects are based on a
number of sources, such as the Hipparcos and Tyco Catalogs (http://astro.estec.esa.nl/Hipparcos/HIPcatalogueSearch.html).
Forms approximately 1600 to 1850, the distances to the Moon, the
Sun, the planets, and the nearby stars were determined with
reasonable accuracy. During this time, astronomers began to
realize the vast size of the Universe far exceeded the distance
scales used by mankind on the Earth. The mile and kilometer
became too limiting to describe the vast distances to nearby
stars and beyond. For the planets, miles and kilometers are
still used for their distances. For a larger view of the Solar
System, the Astronomical Unit (AU), the mean distance of the
Earth from the Sun (1.496 x 1013cm or 92.92 x 106miles), is used
. It describes distances to the outer planets and the Kuiper
Belt of asteroids beyond Pluto and the Oort Cloud of comets
beyond at the outer fringes of our solar system.
Even the AU is, however, too small to easily describe distances
to even the closest of the stars. Here, the AU measurement unit
is supplanted by the light year (5.865 billion miles), the
parsec (3.26 light years), the kiloparsec (3260 light years) and
Mpc (3.26 million light years). However, it is the light year
that has emerged as the most popular measurement to use since it
accents how far back in time we are seeing the images of remote
objects. |
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