How do we know the distance to the stars?

Exploration is in our nature. We began as wanderers, and we are wanderers still. We have lingered long enough on the shores of the cosmic ocean. We are ready at last to set sail for the stars. — Carl Sagan

Ethan Siegel writes: To look out at the night sky and marvel at the seemingly endless canopy of stars is one of the oldest and most enduring human experiences we know of. Since antiquity, we’ve gazed towards the heavens and wondered at the faint, distant lights in the sky, curious as to their nature and their distance from us. As we’ve come to more modern times, one of our cosmic goals is to measure the distances to the faintest objects in the Universe, in an attempt to uncover the truth about how our Universe has expanded from the Big Bang until the present day. Yet even that lofty goal depends on getting the distances right to our nearest galactic neighbors, a process we’re still refining. We’ve taken three great steps forward in our quest to measure the distance to the stars, but we’ve still got further to go.

The story starts in the 1600s with the Dutch scientist, Christiaan Huygens. Although he wasn’t the first to theorize that the faint, nighttime stars were Suns like our own that were simply incredibly far away, he was the first to attempt to measure their distance. An equally bright light that was twice as far away, he reasoned, would only appear one quarter as bright. A light ten times as distant would be just one hundredth as bright. And so if he could measure the brightness of the brightest star in the night sky  — Sirius  —  as a fraction of the brightness of the Sun, he could figure out how much more distant Sirius was than our parent star. [Continue reading…]

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