Now that we have been moving so fast across time, perhaps things will appear to start going slower (hopefully explained in a future relativity post). The 1900’s has created a lot of mind-blowing problems to discuss in our interpretation of the Universe. We’ll get into the whole shabang from the Big Bang to now, but the amount of information to cover from the 1900’s to now cannot really be covered in one post, since such a massive amount did happen. Luckily, not enough to ignite fusion. So we split the 1900’s, perhaps by fission, into three parts.
General discoveries of principles:
Sir James Jeans and Lord Rayleigh developed the Rayleigh-Jeans Law, of course. Rayleigh in 1900 and Jeans in 1905 attempted to predict the relationship between wavelength and temperature for blackbodies. This worked with high wavelengths, but failed catastrophically when it got to lower wavelengths because it showed something called the “Ultraviolet catastrophe.” No, this doesn’t mean Ultraviolet rays were predicted to cause some major problem for humans, but it did show that by Ultraviolet or lower wavelengths the energy should be infinite. With that logic, rays from the Sun or any star should have infinite energy, which is untrue, because then there would be infinite energy in the Universe and spectroscopic data would show infinite temperatures for stars. Oh, also the Earth or any planet wouldn’t be habitable. Most of these statements contradict the data we have (and the fact that we are still alive). Still, another step for science.
To continue from the work of Balmer and all the other people who developed spectroscopy there are two other notables. They are Theodore Lyman and Friedrich Paschen. They both found spectral lines for the emission spectrum of Hydrogen at different wavelengths. Lyman found it in UV wavelengths. Paschen, presumably a passionate man, found the lines in the infrared wavelength. Hot stuff!
To continue from Pickering and his “computers” there are three other extremely important women in Astronomy to discuss. The first is Antonia Maury, who created an early catalog of stellar spectra to help classify them. Unfortunately, her explanation of the different spectral line widths wasn’t liked by Pickering, so she took a leave for almost 10 years. She did come back and analyze the spectral lines of the binary star Beta Lyrae, but she may deserve more credit than it sounds since Ejnar Hertzsprung found value in her work for identifying giant and dwarf stars. Henrietta Swan Leavitt cataloged over 2,000 Cepheid variables, half of the known amount during the time. She also developed the period-luminosity relationship, which was used by Hubble and many others as a method of calculating how far a Cepheid was by comparing its apparent magnitude to the absolute magnitude corresponding to its period. That is up there with one of the most important discoveries in Astronomy and distance calculation. Lastly, there is Annie Jump Cannon. She improved upon the theory of stellar spectra. She created the mnemonic “Oh Be A Fine Girl, Kiss Me”, showing the stellar classes O, B, A, F, G, K, M. Again, still used and very important. Sadly, the three women weren’t given all the credit they deserved at the time, and the same went for pay.
No Astronomy history discussion is complete without Edwin Hubble. They say he could have either been an amazing boxer or basketball player, but instead he went into Astronomy. This is why we make the tough decisions in life. At the time the latest technology was photographic plates, which had to be examined manually. But using them he found many Cepheid variables, and he proved they were outside our galaxy using distance calculations courtesy of Leavitt. He also classified a variety of galaxies, and he found that they were different in distance, shape, and brightness. This is called the Hubble tuning fork since it looks like a tuning fork, and it doesn’t just sound good, it works well enough to still be used. The most famous of his discoveries is calculating Hubble’s Law in 1929 by looking at the redshift of other galaxies and calculating how fast away things are moving relative to us. Using this he was able to create an estimate for the age of the universe, and he showed it was expanding. Besides being famous, he also gets a very nice telescope which showed us such detailed photos that they can almost let us look back in time by looking into the far edge of the universe (our background happens to be part of the Hubble Ultra Deep Field).
Ejnar Hertzsprung and Henry Norris Russell are known mostly for developing the Hertzsprung-Russell or H-R Diagram. This will certainly be discussed in another post since besides showing Astronomers’ love of relationships (they are quite romantic), it visually links luminosity, mass, radius, spectral type, stellar evolution, and most qualities we can tell about a star. Hertzsprung used Leavitt’s work on Cepheids and checked it with parallax to calibrate the relationship. With work put into stellar classes, he found stars had different qualities and stellar evolution could be linked. He also used Maury’s work to show color-magnitude diagrams that link width in stellar spectra to density and size. Russell’s major contribution is the stellar evolution part. With Heinrich Vogt, he showed that mass and chemical composition, but essentially mass, determine the evolution of a star. In general, Russell introduced much of atomic physics to Astronomy which helped develop astrophysics.
Arthur Eddington is known for many things. To start he theorized the interior of stars and in 1914 explained how Cepheid variables pulsate. He also found the Eddington Luminosity, showing the luminosity of a star while it is in hydrostatic equilibrium, which is when the radiation pressure outwards matches gravitational attraction of mass inwards. This means he would of course by 1924 explain the mass-luminosity relationship showing that mass and luminosity produced by a star are related. Eddington also used a Solar eclipse to prove that light is bent from the Sun, major evidence of relativity. He may have need some of his derivations corrected and tried mistakenly correcting others sometimes, but within 10 years he made three extremely important discoveries to Astronomy. We do try to explain things well in this blog, but to quote Eddington himself, “Not only is the universe stranger than we imagine, it is stranger than we can imagine.”
When we mentioned that Eddington incorrectly argued against other people, mainly we are talking about Subrahmanyan Chandrasekhar. He is mostly known for the Chandrasekhar limit (1.44 solar masses), which explains the mass limit for white dwarfs. It also explains how type Ia supernovae are created. So this discovery was of course criticized by Eddington, who didn’t believe pure mathematical derivation could describe something as massive as a star, especially when it involved quantum mechanics which were not completely understood. But Chandrasekhar was right in the end, and he even has the Chandra X-Ray Observatory named after him.
Next we shall tune in to Karl Guthe Jansky, the main person to develop radio Astronomy. By detecting radio waves from the Milky Way Galaxy he showed that a giant dish could be used to detect a variety of objects. Radio Astronomy has revealed many astronomical objects, since energy can be radiated in all different parts of the electromagnetic spectrum. It can also be used to detect and calibrate distances, so it is a truly top-notch, or should we say large wavelength, discovery. Bell Labs should also be noted since not only did Jansky make his discovery there, but much of modern technology was developed there. He gets all sorts of radio Astronomy-related things named after him, from a unit to a prize.
It may be as confusing as relativity at times, but it has to be mentioned (in fact, it even conflicts with general relativity, which shows how the universe is just confusing). Everything in science must be approached, so we shall look at the development of Quantum mechanics. Some main people would be Max Planck, Albert Einstein, Erwin Schrodinger, J. Robert Oppenheimer, Richard Feynman and Werner Heisenberg, in no particular order. Quantum mechanics shows how particles interact, how light seems to be both a wave and a particle, how classical explanations of physics don’t work on a quantum scale, how position and momentum cannot be both determined at the same time, and pretty much showing how we can always screw with physics just a bit more. Of course, it isn’t all about cats, so how does this relate to Astronomy? For one it solved problems like how Wien’s Law and the Rayleigh-Jeans Laws didn’t work, because Planck came along and decided that it isn’t an ultraviolet catastrophe. In general, theories about stars eventually involve things on an atomic scale, so quantum forces should be considered in how a star forms or how light travels.
Another thing to mention is that by this point we still weren’t totally sure where light from the Sun, and stars in general, came from. Luckily, we have a whole slew of scientists to thank for figuring this one out. To start we have F. W. Atson who developed measurements of atoms; his work was used by Eddington to theorize fusion. Next Hans Bethe, who is given the most credit, gave greater proof that Hydrogen fused into Helium to create enough energy to light up the Sun. But there is still more. Since stars have different compositions someone, namely Carl Friedrich Freiherr von Weizsäcker, showed that carbon, nitrogen, and oxygen are involved in fusion for higher mass stars. Last to note was some heavy news from Fred Hoyle who said that iron can’t fuse into heavier elements, even with such high energies.
Another person on this long list is Walter Baade. He looked to the stars, so much so that he found that there were differences between Cepheid variables. This is linked with the discovery of stellar populations (that he also discovered), that a star’s age affects its composition and overall older and newer stars can be differentiated. With this, he found that certain Cepheid had different periods, which would change most calculations done before the time that used the variable stars to calibrate distances. This is why Astronomers must always check their work.
If one read the “Preparing for Competition” part of this blog one may have noticed a certain statement about Swiss Cheese. But a more important Swiss Astronomer is Fritz Zwicky. With Walter Baade he coined the term “supernova”, was the first to theorize neutron stars, and proposed that Type Ia supernovae could be used as a “standard candle.” What this means is that these supernovae can be used to map out extremely large distances because they are all very similar. Zwicky did work on a galactic scale, literally, since he did work about galaxies, their size, and their mass. Knowing from Einstein that light mass can bend light he discovered gravitational lensing with galaxies in 1937, which means that we can sometimes see behind galaxies or show that we may have distortions in our views of galaxies. But even with this he still has his most famous discovery of dark matter. You know, the other thing they are looking for over at CERN. Zwicky used something called the virial theorem to show that there is certain mass in galaxies that can’t be seen. It’s pretty important considering it could make up more of the universe than the regular matter we are made of.
With discoveries about galaxies comes another woman, Vera Rubin. Despite being denied to Princeton, she was able to go to Cornell to gain a higher level degree in her passion of Astronomy. After trying to decide on a topic, she took to galaxy rotation rates. It was expected that similar to our own Solar System, the rotation rates would be slower on the outside of the disk of the galaxy than the center. But after taking spectroscopic data she and her adviser, Kent Ford, found that the edges of galaxies rotated pretty much as fast as the center. At first it was surprising, but after looking at other galaxies and at the observations made by Zwicky she found further evidence for dark matter.
Chushiro Hayashi was a Japanese astrophysicist, so we know he did something awesome. He made a contribution to the Alpher-Bethe-Gamow or αβγ paper, which showed how elements were created in the Big Bang and which ones would be more abundant. He showed that something called electron-positron pairs, which were present in the early universe, should be taken into account. This led to a more accurate proportion of the presence of elements like Helium. But besides this his more eponymous discoveries are the Hayashi track and Hayashi contraction, which shows that the evolution of protostars, or stars that are just beginning to develop (not necessarily as cute as babies sadly), can be plotted on an H-R diagram. The Hayashi contraction itself is when a protostar condenses into a main sequence star; he showed the temperature at which protostars would maintain hydrostatic equilibrium.