1800-1900: Developing a New Understanding of Physics in Astronomy

After a large amount of data, theorizing, and screwing with physics we come to the 1800’s.  Here we bring further data/discoveries, but we also come to a point where physics starts to really become confusing.  Especially when we throw in calculus because, well, it’s integral.  The advent of spectroscopy and discoveries about Optics shed light on many aspects of stars and Astronomy.  Lastly, there were some shocking aspects of electricity and magnetism that had to be looked into.

To start we still have the Herschel family.  William Herschel’s son, John Herschel, was a prominent Astronomer in his own respect.  He wrote about chemicals and photography in 1819, and in 1822 he published a minor work on calculating eclipses of the moon.  But more importantly, Herschel worked with double or binary stars.  He made a whole catalog of them (taken from his father’s work on calculating parallax), and also studied the common center of gravity for a binary system.  One of his most important discoveries was that a force coming from the Sun seemed to be acting on Halley’s Comet, leading to the discovery of solar winds.  After this foray into Astronomy, Herschel continued his work with photography.  He is never actually recognized as its inventor, but he did coin the word “photograph” in 1839.

From all the results of John Herschel’s work on photography, someone had to go and use it.  That man would be Henry Draper.  In 1880, he took the first picture of a nebula (the Orion nebula to be exact).  His overall contribution to Astronomy is improving upon astronomical photography and combining this with photographing stellar spectra.  This was essential to the fantastic vistas provided today; the banner on the top of this blog wouldn’t exist if it wasn’t for the many great high-quality photos of nebulae.

We can now go closer (let’s call this a blueshift) to Christian Doppler.  Usually, he is noted for discovering the Doppler principle/effect/shift, but he’s most notable for that since he didn’t do too much more.  Some of the things he found about it were actually incorrect, but nonetheless, it was an extremely important principle.

Now we will discuss the important discoveries made in spectroscopy during this time.  It really started with Joseph von Fraunhofer in 1814.  He found that dark lines were created when light from a continuous spectrum was absorbed.  Fraunhofer found that light from the Sun had these lines, and by comparing the solar spectra to lines created by gaseous elements, he showed that the Sun was really a hot sphere of gases.  About 50-60 years later, Gustav Robert Kirchhoff and Robert Wilhelm Bunsen explained the cause of these lines.  Kirchhoff is also known for his work with thermochemistry and thermal emission. From this we go to William Huggins. We are unsure whether he was the most huggable man as his name may suggest, but he developed the technique of spectroscopy to look at the stars and accurately show their composition.  This combined with the Doppler Effect created a fantastic new way to look to stars and their properties.

All the Fraunhofer lines from the Sun, just not on one line since that wouldn’t fit

Hopefully we’ve excited you (like hydrogen electrons), since Johann Jakob Balmer is the next man who worked with the up-and-coming field of spectroscopy.  His main accomplishment is the Balmer series of Hydrogen spectral lines.  This shows that Hydrogen has certain spectral line emissions in the visible wavelength, and they can be calculated.  This is important in connecting measurements of the Doppler effect on an object with spectral lines, or it can show the presence of Hydrogen in an object.  Interestingly, by the time Balmer published his very important papers he was 60, and 72 by the time he finished publishing his work, so it’s never too late to do something great.  In addition to him, it is necessary to mention Johannes Rydberg, who showed that the spectral lines produced by atoms can be related and their energies can be found using a formula he created.  The reason we mention Rydberg is that Balmer created his own formula to show the Balmer series, but it was actually a special case of the Rydberg formula.

There are three last people who did some physics-related nonsense. They are Ludwig Boltzmann, Josef Stefan, and Wilhelm Wien.  This nonsense was all about blackbodies (objects that emit energy “perfectly”) and stars are generally treated as blackbodies.  Stefan showed how to determine the power of the radiation emitted by a blackbody and determined the approximate temperature of the Sun.  Boltzmann, a student of Stefan, showed how this can be found mathematically, and also predicted a variety of atomic properties.  Lastly, there is Wien who developed a law that shows that the wavelength emitted by a blackbody changes with temperature.  Altogether, these people did some hot stuff.

Then there is Williamina Fleming.  She was a housemaid to Edward Pickering until one day Pickering got fed up with his male assistants at the Harvard Observatory, and legend has it, declared that his maid could do a better job.  She did.  Fleming classified over TEN THOUSAND stars according to the strength of their hydrogen spectral lines (this classification would be improved by Annie Jump Cannon in the 1900s).  She also discovered many nebulae, novae, and variable stars, including the famous Horsehead Nebula, but she was denied credit for the discovery.  Fleming was later put in charge of the Harvard Computers, also known as “Pickering’s harem”, a group of women who worked as human computers and made many important discoveries in astronomy.

The Horsehead Nebula. Not that easy to find!

Now that we have gotten past a majority of the physicists there was still work being done with distances and planets.

Friedrich Bessel is credited with observing over 3,000 stars, but more importantly, he was one of the first people to use parallax to find the distance to a star.  Parallax is possibly one of the most useful tools in any Astronomer’s arsenal since it is so simple to use, and so important that it will be explained separately in a later post.

Johann Gottfried Galle is next mentioned mainly because he found Neptune using data from Urbain LeVerrier (who may be more important since he also predicted its orbit), but it is nonetheless the last planet of our Solar system.  He also found and studied  414 comets and a crater on the moon.  For this, Galle has a ring of Neptune named for him.  On the subject of Neptune, it is also worthy to mention William Lassell, who discovered Neptune’s largest moon Triton.

To continue with the moon-discovering, Asaph Hall found Mars’ moons Phobos and Deimos, named for gods of fear and terror.  But the only thing that’s scary in this situation is why it took so long.  This is because these moons are REALLY small, as in only a few kilometers across.  Besides this, Hall found the orbits of satellites for other planets, double stars, the rotation of Saturn, and the mass of Mars.

The last thing to mention would be the Yerkes Observatory in Chicago, made in 1897.  It was a giant refracting telescope, able to take vast collections of photographic plates.   This is considered almost a transition to modern Astronomy, because the telescope was state-of-the-art technology and could be used to get the best and brightest photos of space.

The telescope at the Yerkes Observatory. A person doesn’t look like much compared to it!

Other people to mention:

  • Samuel Heinrich Schwabe – Effectively found the sunspot cycle
  • James Clerk Maxwell – One of the most famous physicists of the 1800’s, best known for his equations involving electricity, light, and magnetism.  He also predicted Radio waves and explained that Saturn’s rings weren’t solid or fluid, but rather a bunch of small, separate, solid particles.
  • Lord Kelvin and Hermann Von Helmholtz – worked with star formation, created the Kelvin-Helmholtz mechanism to explain how stars produce energy through gravitational collapse

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This entry was posted in History.

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