How to Measure Stellar Distances With the Parallax Method
A step-by-step guide to understanding how measuring a tiny angle can give us the key to knowing stellar distances
How far away are the stars? Human beings have been asking themselves that question since the dawn of time. Philosophers and astronomers of antiquity imagined that those luminous dots visible in the night sky, some brighter, others dimmer, were very distant worlds, somehow similar to the Sun or the Earth. But how to measure their distance?
In fact, a brilliant, theoretically correct method was devised over two millennia ago. Aristarchus of Samos, an astronomer who lived between the third and second centuries BC, had understood that it is possible to use the properties of right triangles to derive the Sun’s distance. Unfortunately, due to the lack of adequate technologies, he ended up vastly underestimating that distance, which he put equal to only 19 times the Earth-Moon distance instead of 390 times, the value we know today to be correct.
Another 18 centuries had to pass before the distance to the Sun, by far the closest star to Earth, could be calculated with an acceptable approximation. The enterprise succeeded in the second half of the 17th century by Christiaan Huygens and Giovanni Domenico Cassini, who…
