Each in a class of their own…

Ever wonder what makes stars different from one another? Lots of factors can come into play: size, composition, temperature, and age to name a few. Thankfully many stars are similar and can be grouped together by similarities. So here let’s talk about the history and science of stellar classification.

Shedding some light on spectra

In the middle of the 19th century, a German physicist by the name of Gustav Kirchhoff was doing a lot of research into the field of spectroscopy; collaborating closely with Robert Bunsen, inventor of the best piece of scientific equipment high schoolers are allowed to use. Kirchhoff in his research, came to the conclusion that spectroscopy was governed by three basic laws. These are known today as “Kirchhoff’s laws of spectroscopy” (not to be confused his circuit lawslaw of thermochemistry, or law of thermal radiation– basically this guy made more laws than Congress). Kirchhoff’s laws of spectroscopy dictate that:

  1. A solid (or liquid or gas under high pressure) will give off a continuous spectrum.
  2. A gas under low pressure (i.e. most gases we know of) will produce bright, discrete lines known as an emission spectrum.
  3. If you look at a source of a continuous spectrum from behind a source of an emission spectrum, you will see what looks like a continuous spectrum with black lines missing from it; think of if you took the emission spectrum and subtracted it from the continuous spectrum. This is called an absorption spectrum.

An example of Kirchhoff’s laws of spectroscopy. On the left you see an example of a continuous spectrum (Law 1) and an emission spectrum (Law 2) on the right. In the middle is an example of an absorption spectrum (Law 3), basically the removal of the emission line from the continuous spectrum. Credit: Penn State

Kirchhoff asserted that the wavelength or location of these emission or absorption lines was determined by what atoms or molecules were present in the source. This is true because each element or molecule has a unique atomic spectrum or signature. At the time that Kirchhoff came up with these laws scientists had yet to crack the secret of the internal structure of the atom. Meaning Kirchhoff made these laws based on purely on experimentation. It took another half a century for Niels Bohr to come up with a correct model of the atom that concluded the existence of discrete energy levels that successfully explained Kirchhoff’s emission and absorption lines (and later led to the formulation of quantum mechanics).

Enter the Harem

So back towards the end of the 19th century, a man by the name of Edward Pickering was the director of the Harvard College Observatory. Mr. Pickering decided to take it amongst himself to obtain spectra of as many stars as he could and then index and classify them. So Pickering did what any good scientist would do, he began to collect data. But as you well know, there are a lot of stars in the sky, so before he knew it he was inundated with tons of photographic plates (if you thought film was bad, its predecessor was worse- these plates were usually large heavy pieces of glass mixed with silver salts) containing stellar spectra. Legend has it that Pickering was getting so aggravated by the incompetence of his male research assistants that he exclaimed that his maid could do a better job. So he hired her. Her name was Williamina Fleming and along with Pickering she helped to publish the Draper Catalogue of Stellar Spectra (named in honor of Henry Draper, the first man to take the spectrum of a star on a photographic plate), which had classifications for 10,351 different stars. Once Fleming left Pickering’s service, he hired several other women assistants. Out of this group of women, which became known officially as the “Harvard Computers”, but commonly as “Pickering’s Harem”, came some of the greatest early female astronomers, including Annie Jump CannonHenrietta Swan Leavitt, and Antonia Maury. The initial version of this catalog, published from 1918 to 1924 in 9 volumes, included the positions, magnitudes, and spectral classifications of over 225,000 stars.

Edward Pickering and his “harem” outside a Harvard building in 1913. Annie Jump Cannon stands two to the right of Pickering. Credit: UC- Berkeley

Differentiating the spectral classes

Alright, so how does that help astronomers? Well, in essence a star is a gas under high pressure, meaning it should give off a continuous spectrum according to Kirchhoff’s first law. But the outer layers of a star’s “atmosphere”, called the corona, is a gas under low pressure- meaning we actually see an absorption spectrum (Law 3). (In fact, it was the unexpected discovery of this absorption spectrum that helped us to realize that our Sun had an “atmosphere” or outer layer of hot gas surrounding it.) Since stars of the same size and mass are made up of pretty much the same stuff, they have similar spectra. In fact, this is how astronomers classify stars, by their spectral class. The different stellar spectral classes are O, B, A, F, G, K, and M. Type O stars are the hottest and Type M stars are the coolest. Each spectral class or spectral type has a unique spectrum.

Recreated stellar spectra of each spectral type (from top to bottom): O, B, A, F, G, K, M. Credit: ESA

With a name like that…

Now, like a lot of things in astronomy, this naming scheme is totally absurd and illogical. I wish I had a better explanation for why we have this naming scheme, but basically it’s a historical holdout from back when astronomers started classifying stars without really understanding them. Remember the Harem? Well in the first publication of the catalog in 1890, Williamina Fleming did most of the classification. She used a classification system that had been developed a few decades earlier by the Italian astronomer Angelo Secchi. Since she had so many stars, she took Secchi’s five classes and stretched them out to encompass fourteen classes from A to N. Then she added three more categories (O, P, Q) to encompass stars that would not have fit Secchi’s scheme. A through Q made sense. But then in 1897, Antonia Maury was working on a different set of stars and decided to reclassify what Fleming had done. So she scrapped the letters and made 22 classes from I to XXII…still made sense. Unfortunately, in her rearranging of Fleming’s classes, she wasn’t paying attention to the letters and moved some around, hence O and B moving towards the front.

Finally in 1901, Annie Jump Cannon (probably the most famous and accomplished of the Harem) was cataloging and decided to go back to the letter system and dropped all the letters except O, B, A, F, G, K, and M in that order. Why? I have no idea. For some reason after Ms. Jump Cannon came up with her system they had had enough reclassification and no one suggested, “Hey maybe we should have these make some kind of logical sense.” Astronomers can be infuriating sometimes.  The final crazy product is known today as the Harvard Spectral Classification. So, if you need a way to try to remember Ms. Jump Cannon’s crazy archaic classes, try “OBA Fine Gal (or Guy), Kiss Me!” Of course, the cockamamie lettering system wasn’t enough, Ms. Jump Cannon then needed to add ten subclasses from 0 to 9 for each letter. Meaning not only is a B-type star hotter than a K-type star, but a B1 star is hotter than a B5. Our star, the Sun, is a G2, meaning it’s pretty much right in the middle of the stellar pack.

Digging even deeper

But somehow the crazy letter and number combination still wasn’t quite exact enough. In 1943, three astronomers from the Yerkes Observatory in Wisconsin came up with another classification system that focused not only on the surface temperature of a star (which the Harvard Classification does), but also on the luminosity (or brightness). Basically, you can have a really big red giant star and a teeny tiny white dwarf star that are the same temperature and therefore have similar emission lines. However, you can look at how sharp those emission lines are and determine the surface gravity or pressure that that star must have. When introducing this new factor into the equation, the Yerkes astronomers came up with seven (I-VII) new classes that basically help to dictate what stage of life a star is in.

To try to help this make some visual sense, astronomers have developed a graph called the Hertzsprung-Russell diagram that correlates how bright a star is, how hot it is, and what spectral class it’s in. This pretty ingenious and very common graph helps to simplify a vast amount of knowledge. It’s really pretty obvious how the groups appear when looking at a filled out H-R diagram. Most stars, like our Sun (which is a G2V), are in class V, meaning they are still on the “Main Sequence” and are still fusing hydrogen into helium. As stars live and evolve, they move off of the main sequence and into other branches of the H-R diagram. Can you pick out where the Sun would be on this H-R diagram below?

A Hertzsprung-Russell diagram showing the major classes of stars. The temperature (and spectral classes) run from hottest to coldest, left to right. Generally size decreases from top to bottom. The “Main Sequence” is the diagonal line running through the middle, with the other evolutionary branches around it. Credit: Wikipedia

Famous Scientist Profile: Nikola Tesla…

Think about your favorite scientist. Okay, so realistically you probably don’t have an actual “favorite” scientist, but most of you probably thought Einstein, right? Not surprising. Albert Einstein is without a doubt the most notable and famous scientist of the last century, having reached a celebrity status that no scientist before him and very few after have even come close to. Now some of you more hip, savvy science-minded cats out there may have said Carl Sagan or Neil deGrasse Tyson or Richard Feynman or others, but those guys are more famous for being science popularizers than scientists (well Sagan and deGrasse Tyson at least), and I’d say any of those three is perhaps in the parking lot of the same ballpark as Einstein. Einstein’s kind of a big deal, people know him. You have to be pretty “nerdy” to know Feynman. In any case, some might say that Einstein was simply a character that was created by the popular media of the day (photography, radio, magazines, early TV, etc.) which allowed a greater spread of information (the same way TV and the internet have helped Sagan and deGrasse Tyson), but the bottom line is that Einstein basically became the personification of genius. His name become synonymous with superior intelligence. Now that my friends, that’s notoriety.

Nikola Tesla: that mustache can’t hide the genius!

In any case, I guarantee that none of you answered the question of who your favorite scientist is with the man pictured above. That’s Nikola Tesla. And that’s really a shame because he probably had a more significant impact on the development of the modern era than any single person in history. And when you hear “Tesla”, you probably think of loud coil things that shoot out awesome sparks or fancy electric cars. But I’m sure you probably know very little about the actual genius and significance of the man that basically gave birth to modern electricity.

Nikola Tesla was born on July 10, 1856 in Smiljan, a small mountain village in what is now Croatia, but what was then just part of the Austrian Empire. Nikola was born to Milutin Tesla, a Serbian Orthodox priest, and his wife Đuka, who interestingly enough never even learned to read. Nikola was the fourth of five children and the only surviving son (his older brother was killed while riding a horse when Nikola was 5). From very early on, it was clear that Nikola was special. While in school he could supposedly do integral calculus in his head, a feat so astounding that his instructors were convinced that he was cheating. (Note: I don’t know if you’ve ever done integral calculus, but it’s pretty difficult to do with a textbook and a calculator, let a lone doing in your head.) It also didn’t hurt that he supposedly had a photographic memory.

In any case, he attended to the Austrian Polytechnic in Graz, Austria and studied to be an engineer. He never even finished his degree, but was genius enough that he had no problem finding engineering work without it. He ultimately moved to Budapest in 1880 and began working for the Hungarian National Telephone company.

Now around the same time, the guy who we all think of as the father of electricity, you know Thomas Edison (pictured below) was working like a madman in his Menlo Park, NJ laboratory, trying to supply the world with all of his new electrical inventions. By the way, Thomas Edison DID NOT invent the light bulb, in fact, in their book Edison’s electric light: biography of an invention, authors Robert Friedel and Paul Israel compiled a list of 22 inventors who came up with incandescent lamps before Edison. Edison’s light bulb was just way better. And he was able to produce and sell it. It’s similar to Galileo and the telescope: it wasn’t his invention, but he popularized its use for astronomy and history favors the victors, as they say.

Thomas Edison: American inventor & villain

Anyway, Edison was working like a crazy electrical fool in New Jersey, trying to supply the United States and Europe with his amazing new electrical inventions. In 1882, Tesla got a job in Paris working for the Continental Edison Company, basically improving Edison’s designs as they got shipped over to Europe from the States. In 1884, Tesla moved to the U.S. and got a job working for Edison. This must have been similar to Heisenberg working under Bohr in the 1930’s. Edison knew he had a prized asset in Tesla, and he exploited the bejeezus out of him. A perfect example:  In 1885, Tesla told Edison that he could vastly redesign and improve the horribly inefficient Edison motors and generators and Edison offered Tesla $50,000 if he could actually follow through with it. After a few months of work, Tesla succeeded and when he went to Edison to ask for the reward, Edison shrugged him off and said that he was only kidding. Edison did offer him a raise though, an extra $10 on top of his $18 a week salary. Tesla promptly refused and quit.

After that Tesla bounced around from electric company to electric company and for stints had to work as a ditch-digger to make ends meet. He partnered up with George Westinghouse and for awhile worked at Westinghouse Electric & Manufacturing Company. In fact, it was while partnering with Westinghouse that Tesla helped to supply electricity to the 1893 World’s Columbian Exposition in Chicago. The success of that feat was huge because the pair were able to successfully demonstrate the safety and reliability of alternating current (AC) to Americans who were being lied to about it by Edison. Oh right, so here’s where you find out about the other side of Thomas Edison, the side the history books and encyclopedia articles don’t tell you. Edison was totally the villain in this story. In the “War of Currents”, Edison became a fierce rival of Tesla and Westinghouse because he was trying to sell/promote the direct current (DC) system of supplying electricity, as opposed to the alternating current system that Tesla came up with. You can click here to get a quick explanation of the differences in AC and DC currents, but it basically boiled down to the fact that AC was more efficient because it operates with a lower current, so there is little power and energy dissipation, even over exceptionally long distances. Anyways, Edison, with his crazy fame, power, and influence over the American people, began a huge smear campaign against Tesla and alternating current, even going so far as to electrocute puppies as a “demonstration” of how dangerous AC power could be. Even though Tesla’s AC system was more efficient (and is now what we all use in our homes today), Edison’s smear campaign took its toll and is probably one of the biggest reasons why Americans have very little idea who Tesla even is, let alone the impact he had on the world.

Nikola Tesla would often run alternating current (AC) through his own body to demonstrate to the public that it was not as unsafe as Thomas Edison claimed.

In addition to the invention of alternating current (which in itself was amazing), Tesla is also recorded having come up with the idea of the radio before Guglielmo Marconi and radar before Robert A. Watson-Watt. He also supposedly discovered X-rays before Wilhelm Röntgen, theorized the electron before J.J. Thomson found it, built the first hydroelectric plant at Niagara Falls, experimented with cryogenic engineering way before anyone else, was the first person to record radio waves from outer space, discovered the resonant frequency of earth a half-century before anyone else, etcetera, etcetera, etcetera…the list of amazing accomplishments goes on and on. Basically what it boils down to is that Nikola Tesla was AMAZINGLY BRILLIANT and super ahead of his time AND BARELY ANYONE EVEN KNOWS ABOUT HIM!! Oh and I almost forgot, he also died alone in a NYC hotel room, in love with a pigeon. I mean if that story doesn’t scream Academy-Award-winning caliber movie, I really don’t know what else does. I can see Robert Downey, Jr. playing an amazing Tesla.

Which is why I proudly celebrate Nikola Tesla Day every July 10 (you can still celebrate it belatedly), in memory of this truly awesome man. Oh and if you want a really amazing little recap of why Nikola Tesla is so awesome, I point you to possibly my favorite comic from The Oatmeal, entitled “Why Nikola Tesla was the greatest geek who ever lived.” or the Tesla post on bad***oftheweek.com, with the disclaimer that both have some adult language.

<I apologize that these links here at the end have adult language, but I can’t censor them. And apparently people just get very emotional when talking about Nikola Tesla. In any case, I definitely feel that their benefits outweigh the negative of them including bad language.>

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