The Shadow and the Moon

This is another story about lunar eclipses and the thrill of scientific discovery. As you might know there was quite a buzz about yesterday’s total lunar eclipse, the last one until 2011 or so. I felt a little indifferent to it. After all, what's the deal with an eclipse? Maybe during the Ming dynasty you could attain glory and celebrity status if you were able to predict one, but we've known for a while that it's just the earth sneaking in between the moon and sun, and even your local news weather guy could tell you up to the minute when it'll occur.

Then I got a call from my friend Joerg (a math student), asking if I knew whether the MSU observatory, the big telescope in the farmlands of MSU's campus, would open for the event. And so this eclipse thing began to bug me - I have a small telescope I got as a chirstmas gift from my girlfriend, which is sleeping in my closet and never gets much use, so I should use this not in the next 4 years event to take it out. Besides, the moon is the only astronomical object I can guarantee I'll locate with the telescope - I could get jupiter once though, but only because it was low in the sky and easy to find relative to one of the apartment blocks in my complex; it was a brief sighting until it moved too low and we were suddenly infringing some of my neighbors privacy constitutional rights!

I talked to a couple of friends and set up a astronomy in your backyard night. Ana, a fellow grad student at the lab, was the only one brave enough to face the impossible cold night and show up. The moon looked a little disappointing, just grey and diffuse, and no hints of the poetic reddish tones everyone was talking about. Just when the two pairs of socks and gloves were becoming insufficient for cold, Ana took out a digital camera from the pocket and pointed it at the telescopes eye piece. Que queres hacer?! But suddenly voila! a bright white crescent magically flashed in the lcd screen (the eclipse was ending and one side of the moon was beginning to reflect the sun). Needles to say, we stayed for quite a while taking pictures:

Isn't it great?! We'll i know, it's like a newborn baby, ugly like 99% of all newborn babies, but you can't just say that to the drooling parents. This might be the worst pictures of an eclipsed moon you might find (I have a few more here), but it's amazing you can get this with the simplest digital camera and telescope in ebay; and you are suddenly deserve your place in the ranks of amateur astronomers - also missing a couple of fingers to frostbite adds to the feeling of accomplishment.

As serious astronomers, we're not content with just pretty pictures. As serious scientist, we're utterly skeptic. The giants we're standing on (the scientist of the past) claim the earth is larger than the moon, but who knows.... If we pretend the sun is very very far away then the shadow of the earth on the surface of the moon should have the same size as the earth, and we can compare the size of the moon with that of the earth from the photo. What i mean, in the little diagrams physicists love so much, is this:

So if we now use our precise measurement:

We get that the moon is 73/177=0.412 times smaller than the earth. There you go, i've earned my PhD! (the actual value is 0.273, so that's not so far off; if you go to the store and ask for a pound of salami and the employee is a little distracted and gives you 1.5 pounds you'll probably also take it)

In the next public viewing there will be tequila. That should attract a larger crowd and mitigate the weather.


This work has been supported in part by a generous grant from the M.M. Henry Foundation for the Advancement of Uruguayan Astrophycisits