This book continues our exploration of cosmology,
the science of the universe as a whole.
Here we examine one of the greatest challenges and most important
accomplishment of astronomy and cosmology: measuring the distance to
remote celestial bodies. We will discover how astronomers used their
wits and centuries of meticulous observations to precisely measure the
size and evolution of our universe.
In an ideal world (or universe), a magical instrument would tell us the
distance to at any celestial body we wished. Unfortunately, there’s no
such thing in this world. Astronomers can measure positions across the
sky with extreme precision. They can also precisely measure the
composition of celestial objects, and how fast they are moving toward
or away from us. But, when asked about that twinkling little star,
astronomers still struggle with “...how I wonder where you are.”
Cosmic distance measurement has a critical role in cosmology. Almost
everything we claim to know about our universe — its size, its
expansion, changes in expansion rate, its age, and its history —
depends on measuring cosmic distances. Thus distance measurement has
long been, and continues to be, one of the greatest challenges in
astronomy and cosmology.
have tried every conceivable technique to measure cosmic distances —
several dozen schemes were significant enough to be named and described
in the research literature. This eBook focuses on what ultimately
emerged from these struggles: the cosmic distance ladder.
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