An unfamiliar knock at my office door — more of a tap than a knock. “C’mon in, the door’s open.”
“¿Está ocupado?”
“Hi, Maria. No, I’m not busy, just taking care of odds and ends. What can I do for you?”
“I’m doing a paper on Vera Rubin for la profesora. I have the biographical things, like she was usually the only woman in her Astronomy classes and she had to make her own baño at Palomar Observatory because they didn’t have one for señoras, and she never got the Nobel Prize she deserved for discovering dark matter.“
“Wait, you have all negatives there. Her life had positives, too. What about her many scientific breakthroughs?”
“That’s why I’m here, for the science parts I don’t understand.”
“I’ll do what I can. What’s the first one?”
“In her thesis she showed that galaxies are ‘clumped.’ What is that?”
“It means that the galaxies aren’t spread out evenly. Astronomers at the time believed, I guess on the basis of Occam’s Razor, that galaxies were all the same distance from their neighbors.”
“Occam’s Razor? Ah, la navaja de Okcam. Yes, we study that in school — do not assume more than you have to. But why would evenly be a better assumption than clumpy?”
“At the time she wrote her thesis the dominant idea was that the Big Bang’s initial push would be ‘random’ — every spot in the Universe would have an equal chance of hosting a galaxy. But she found clusters and voids. That made astronomers uncomfortable because they couldn’t come up with a mechanism that would make things look that way. It took twenty years before her observations were accepted. I’ve long thought part of her problem was that her thesis advisor was George Gamow. He was a high-powered physicist but not an observational astronomer. For some people that was sufficient excuse to ignore Rubin’s work.”
“Another excuse.”
“Yes, that, too.”
“But why did she have to discover the clumpy? You can just look up in the sky and see things that are close to each other.”
“Things that appear to be close together in the sky aren’t necessarily close together in the Universe. Look out my window. See the goose flying there?”
“Mmm… Yes! I see it.”
“There’s an airplane coming towards it, looks about the same size. Think they’ll collide?”
“Of course no. The airplane looks small because it’s far away.”
“But when their paths cross, we see them at the same point in our sky, right?”
“The same height up, yes, and the same compass direction, but they have different distances from us.”
“Mm-hm. Geometry is why it’s hard to tell whether or not galaxies are clustered. Two galaxy images might be separated by arc-seconds or less. The objects themselves could be nearest neighbors or separated by half-a-billion lightyears. Determining distance is one of the toughest problems in observational astronomy.”
“That’s what Vera Rubin did? How?”
“In theory, the same way we do today. In practice, by a lot of painstaking manual work. She did her work back in the early 1950s, when ‘computer’ was a job title, not a device. No automation — electronic data recording was a leading-edge research topic. She had to work with images of spectra spread out on glass plates, several for each galaxy she studied. Her primary tool, at least in the early days, was a glorified microscope called a measuring engine. Here’s a picture of her using one.” 
“She looks through the eyepiece and then what?”
“She rotates those vernier wheels to move each glass-plate feature on the microscope stage to the eyepiece’s crosshairs. The verniers give the feature’s x– and y-coordinates to a fraction of a millimeter. She uses a gear-driven calculating machine to turn galaxy coordinates into sky angles and spectrum coordinates into wavelengths. The wavelengths, Hubble’s law and more arithmetic give her the galaxy’s distance from us. More calculations convert her angle-angle-distance coordinates to galactic x–y-z-coordinates. Finally she calculates distances between that galaxy and all the others she’s already done. After processing a few hundred galaxies, she sees groups of short-distance galaxies in reportable clusters.”
“Wouldn’t a 3-D graphic show them?”
“Not for another 50 years.”
~~ Rich Olcott
“So you’re telling me, Cathleen, that you can tell how hot a star is by 
Cathleen turns to her laptop and starts tapping keys. “Let’s do an example. Suppose we’re looking at a star’s broadband spectrogram. The blackbody curve peaks at 720 picometers. There’s an absorption doublet with just the right relative intensity profile in the near infra-red at 1,060,190 and 1,061,265 picometers. They’re 1,075 picometers apart. In the lab, the sodium doublet’s split by 597 picometers. If the star’s absorption peaks are indeed the sodium doublet then the spectrum has been stretched by a factor of 1075/597=1.80. Working backward, in the star’s frame its blackbody peak must be at 720/1.80=400 picometers, which corresponds to a temperature of about 6,500 K.”
“You’re right, Sy. It’s not a particularly pretty picture, but it shows that nice strong sodium doublet in the yellow and the broad iron and hydrogen lines down in the green and blue. I’ll admit it, Vinnie, this is a faked image I made to show my students what the solar atmosphere would look like if you could turn off the photosphere’s continuous blast of light. The point is that the atoms emit exactly the same sets of colors that they absorb.”
“Whoa, Sy. Do you read the final chapter of a mystery story before you begin the book?”
“It is, Sy, and that’s one of the reasons why Hubble’s original number was so far off. He only looked at about 50 close-by galaxies, some of which are moving toward us and some away. You only get a view of the general movement when you look at large numbers of galaxies at long distances. It’s like looking through a window at a snowfall. If you concentrate on individual flakes you often see one flying upward, even though the fall as a whole is downward. Andromeda’s 250,000 mph march towards us is against the general expansion.”
“Infinite?”
Those two electrons push their dust grains apart almost a quintillion times more strongly than gravity pulls them together. And the distance makes no difference — close together or far apart, push wins. You can’t use gravity to build a planet from charged particles.”
“Good question. If protons were more positive than electrons, electrostatic repulsion would always be proportional to mass. We couldn’t separate that force from gravity. Physicists have separately measured electron and proton charge. They’re equal (except for sign) to 10 decimal places. Unfortunately, we’d need another 25 digits of accuracy before we could test your hypothesis.”
Hard Science Ain't Hard 
