How do scientists measure distances to stars and galaxies?

Introduction

Many of us know that the sun is approximately 150 million km or 93 million miles away, a distance that is known as the “astronomical unit” (AU). Neptune, the most distant planet, is 30 AU from the sun, or some 44.8 billion km (27.9 billion mi). The Voyager 2 spacecraft, launched in 1977, reached

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Where is everybody?

Introduction

During a lunch in the summer of 1950, physicists Enrico Fermi, Edward Teller and Herbert York were chatting about a recent New Yorker cartoon depicting aliens abducting trash cans in flying saucers. Suddenly, Fermi suddenly blurted out, “Where is everybody?”

Behind Fermi’s question was this line of reasoning: Since there are likely many other

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