The Walk Up Mount Wilson

By cjohnson | August 22, 2005 1:30 am

trip view As you know from an earlier post, I left Aspen on Friday and headed home. This involves changing planes at Denver, and then flying over the strange, beautiful, and changing landscape West to Los Angeles. It only takes about a couple of hours. I was thinking hard about our discussion about the Greatest Physics Paper! and trying to think of those forgotten examples of great work. The people who’s songs are seldom sung. The unglamourous “bread and butter” works that seldom get written up in the newspapers near the time that they are produced, if ever. These solid works are examples of what every scientist should do as a matter of course: You look at the evidence you have before you, gather more if necessary, make some assumptions, form a hypothesis, and test it against the data. Next, come to a conclusion, and report your results as clearly and honestly as you can, and so on.

Whether or not you have some vision about what it all means does not necessarily qualify or disqualify the resulting paper as a candidate for being a great paper. It can still take its place in the tapestry that is the sum of efforts of generation after generation of physicist to make sense of our world, and find its meaning there.

So I was thinking about this all, and my mind switched to some recent reading I’d been doing. Simon Singh’s excellent book, “Big Bang” had been on my bedside table recently, and although I’d not had a lot of time to read it, I was curious to dip into it from time to time. This is partly because, while I know several of the stories and the history that he tells, it is always of great value to see how another tells those stories. I always learn something, either in the facts or in the telling.

As we’d been discussing before, Einstein’s papers are modern examples of work that changed our entire view of how the universe that we inhabit is really put together. How can those fail to be top candidates for the best physics papers ever? Same thing for Newton, and for Galileo, etc.

However, it’s easy to forget that for several years after Einstein’s breakthrough with General Relativity, the world still thought that the entire universe was just the Milky Way Galaxy. It was not until the year 1923 that Edwin Hubble (in one of his many great contributions) established extremely cleanly that the Andromeda Galaxy was several times further away from the center of the Milky Way than the edge of the Milky Way itself. This was a truly shattering change of perspective about our universe’s size and variety: There were now known to be thousands of galaxies out there just like our own. Imagine what that would be like today. It would be like finding that there are thousands of other things out there that are just like the universe we live in today that we thought contained everything. That would turn so much of what we know upside down.

Now Hubble’s work was truly great, of course, and it is interesting to me that he is better remembered for “discovering that the universe expands” (he was not in fact the first to note the expansion of the universe, just the first to quantify it – Hubble’s Law. This is a very important contribution, without a doubt). To my mind, the Andromeda result is far more singular and unambiguous a discovery.

But never mind. My point is this: What was the key foundation upon which Hubble stood to find this astounding Andromeda result? Surely, everybody else had access to the information about the various galaxies (or “nebulae” as they mistakenly called them then) out there? Why did they miss something that seems so obvious to us today?

Ah, here comes one of those great pieces of “bread and butter” physics. The relatively unsung, simple, but absolutely key work of the type that I mentioned before. It was by Henrietta Leavitt, who through painstaking work gathering and analyzing data, and some key assumptions and a bold hypotheses, was able to establish a simple relationship between the average brightness of certain type of star and the rate of pulsation of its brightness. These stars, which periodically vary their brightness, are called “Cepheid variables”. In fact, Leavitt plotted a curve showing the relationship, and most such stars fall close to that curve.

So when you see one of these stars in the sky and measure its pulsing rate, you know how bright it must be. Compare that to how bright it actually is, and you know how far away it is – a whole new “metre rule” (“yardstick” for readers in the USA) of measurement. (Well, it was key that Shapley and Hertzsprung used parallax to fix the distance of a nearby one of these stars to “calibrate” the scale – another excellent piece of work.)

This was the foundation Hubble needed to make sense of the data he was gathering using the 100-inch telescope at the top of Mount Wilson, and it was this sort of less well-known solid piece of work whose existence I was mulling over when the captain of our Boeing 757 announced that we were beginning the approach to the airport. At this very point, I thought “Oh! I should be able to see Mount Wilson”, and I immediately looked out of the plane right over to Mount Wilson and could see two white dots which were probably two of the domes of the observatory. I was sure it was the right mountain since it had a few miles from its base the unmistakable landmark made by the famous Santa Anita racetrack. (Those of you who saw the film “Seabiscuit”, for example, will know a little of the history of that place.)

I am not making this up. I was thinking about Hubble’s work and did just look out upon the very instruments he used. It was magical. So you know what I had to do, of course. I had to go up there that next morning. I’d been planning to go up again sometime soon, since I’d never seen the observatory (I’d been up only once before, with a large part of USC’s Neuroscience department, but it was on such a constantly cold and foggy day that we came back down without ever looking around up there).

mount wilson So I got home, unpacked a little, did some shopping for supplies at the local Trader Joe’s (giving me an excuse to test the bike to see that it had made the return journey in good health – it had), gave my usual explanations about how the bike worked to the usual random inquisitive locals, and came back home and went to bed. The next morning saw me rise at 5:30am and get my gear (sandwich, water, nuts, fruit -the last of the Aspen peaches– , directions, boots, more water, etc) ready to get significantly high up the mountain before the sun got too hot. As it happened, I was later leaving than I intended, but I drove over to the trailhead and bent my back into the task by 7:50am. The sun was already beginning to beat down, actually, but was not yet unpleasant. It was a wonderful hike, and I was thinking about great works of physics for most of the way, and in that frame of mind found it inspiring to be going up the Old Mount Wilson trail where lots of great physicists had tread before.

trip view trip view There was so much to see, but I won’t trouble you with lots of pictures of all of the things I saw, from the wonderful shape of the mountain and the approach of the trail itself to the various flowers, trees, streams, and animals of various sorts. (See a couple on the right and left. The one above is a view of the goal from about a third of the way up.) I’ll cut to the chase. I got up there 2 hours and 45 exhilarating minutes (and 6.8 miles and 2000ft) later. The sun was hot, and I was exhausted, but I wanted to see the telescopes! So leaving lunch for later I rambled around the top of the mountain until I found them, walked around them, looked in at the observation deck of the 100-inch, looked at the smaller solar telescopes on their giant pedestals, generally soaked up the significance and history of the place – and it was great. I don’t know why. I just felt I needed to go up and see them and take a few pictures for you, in order to tell the story right.

Below are the domes containing the 60 inch and 100 inch telescopes:

60 inch dome

100 inch dome

…and this is the 100 inch telescope (yes, the one Hubble used for the Andromeda result):


Here are two views of one of the smaller instruments used for studies of the sun:

solar telescopesolar telescope

There, I’ve done it. I hope it means a little to you too. At least you now know why I was stuck on the sofa for a while again, on Saturday night.



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