Link #151: Bessel Was The First Person To Measure Distance To Stars!


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Link #151: Bessel Was The First Person To Measure Distance To Stars!

Friedrich Wilhelm Bessel (1839 painting)
Portrait of the German mathematician Friedrich Wilhelm Bessel by the Danish portrait painter Christian Albrecht Jensen/Public Domain.

Measuring distances has always been a favourite thing of humanity. We do it because we always want to know how far we are from our destination. In fact, this desire for knowledge of distance is why the ancient Romans invented odometer, as we described in our last article.

Once we had ways of measuring distances on our planet, we became obsessed with measuring distances between our planet and other things in the universe. Naturally, this caused us to focus on stars. Friedrich Bessel was the first astronomer to successfully measure the distance to a star and he did it through pure innovation. How’d he do it? Let us tell you.

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How Did Friedrich Bessel Measure Distances To Stars?

Hubble Parallax
Image credit: NASA/ESA, A.Feild/STScI/Public Domain.

At the time of Friedrich Bessel, most astronomers were trying to prove the fact that Earth orbited the Sun. This was an idea that was initiated by Copernicus. The theory for proving this and measuring the distance to the stars was similar.

The way to find out the distance of a star from Earth and prove that Earth revolves around the Sun could be proven by discovering the parallax of the star. Finding the parallax of a star hinged on precision measurements of star’s movements across the sky.

Friedrich Bessel managed this after a number of innovations and correctional measures. Bessel did this first by eliminating instrument based errors from the recorded positions of a number of stars from a number of astronomers of the time. This seemingly minor fix to the existing system is considered to be the first proper step towards astrometry for humanity.

In the end, Bessel’s earlier corrections to existing systems allowed him to measure the parallax to the star 61 Cygni. The measurement Bessel arrived at was 10.3 light-years, which is not that far from 11.4 light-years that modern equipment has measured.

What Is Parallax Of A Star In Astronomy?

Parallax Animation
Image credit: Nathaniel Domek/CC BY 3.0

The logic was that a star that was nearer to Earth would move back and forth in the sky much faster than a star that is farther. The extent to which a star moves back and forth was dubbed parallax.

This process is similar to what you see in the animation of parallax above – as the viewpoint moves side to side, the objects closer to the camera appear to move faster, while the objects in the distance appear to move more slowly.

What Is Astrometry?

Thousandau1 Space Probe
Image credit: NASA / JPL Public Domain.

You may have heard the term astrometry being bandied about all the space shows and films. Shows like Star Trek are particularly known for using such terms. Since Bessel initiated the whole science of astrometry, can you guess what it involves?

Astrometry is the science of studying and projecting the exact movements and positions of various objects in space. This could include everything from a comet and asteroids to a planet and stars. In simple terms, astrometry helps us explore the universe within and outside our own solar system. In the future, who knows, maybe it will help in mapping galaxies!

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