Tuesday, November 2, 2010

More amateur astronomy!

Last night I had the greatest thrill I've experienced in quite some time, and it might illustrate how boring I'm becoming in my old age. But hear me out.

A couple weeks ago, my grandparents in Delaware sent me home to Jersey with a small gift: a pair of binoculars that had been sitting unused in one of their closets for a number of years. They're by no means the best binoculars I could have in my pocket -- actually, most opical engineers would say they're quite lousy -- but they can still magnify an image, and the price was right.

Between ten and eleven last night I bundled up and ventured outside with the binoculars in one hand and an autumn star chart in the other. It took a bit of time, doing, and numbness of the fingers, but I found it: Messier Object 31, a nondescript grayish smudge in the sky between the triangle formed by Cassiopeia α, Pegasus α, and Pegasus β.

I'm not an expert on the history of astronomy, but I do know a thing or two about 18th century French astronomer Charles Messier. His primary objects of study were comets. Loved them. Wanted to find as many as he could. And more often than he would have liked, he'd fix his telescope on a part of the sky and think he'd found a new comet -- only to discover, after tracking it for a few nights, that his latest candidate didn't move at all like a comet, and therefore could not be one. Messier began to catalogue these objects in a kind of cosmic junk index, so as not to make the same mistakes twice and to mark them out for future comet hunters.

It is truly astonishing how the real fruits of our endeavors are sometimes evinced in the things which we mistake as being incidental -- or even obstructive -- in our progress towards our intended aims. Messier's catalogue is now regarded as his single greatest achievement and contribution to science.

In the 19th century, most of these Messier Objects were identified as nebulae, which I am sure you are familiar with. M31 was no exception -- at least not at first. The closer astronomers looked at it (thanks to improvements in telescope design), the more irregularities they discovered. For a while they believed it was a supernova. Then they decided it must be a newborn star or solar system forming in the center of disk-shaped accretion of gas. Both ideas had to be scrapped following a couple of further discoveries -- one of which had to do with M31's distance from the Earth.

The classical method of calculating astronomical distances is really quite ingenious and elegant. Imagine you have two circles, one inside of the other.

Let's say that at the center of both circles is the astronomical object (let's say a star) under consideration.

Now. Let's take a chunk out of this imaginary larger circle and assign it a value. This is our baseline. Point A is an observatory somewhere on the earth's surface; Point B is an observatory some miles elsewhere that is looking at the same star at the same time. (A greater distance between Point A and Point B makes for a more accurate measurement.)

Now. In a nutshell (and skipping a few steps), the ratio of arc AB to the circumference of the greater circle is going to be equal to that of the parallax angle to the 360 degrees of the smaller circle:
(AB/2πx) = (parallax/360)

But what's parallax, you ask? That's easy. Hold your index finger close to your face and shut one eye. Now shut that eye and open the other. Notice how your finger seems to change position with regard to objects in the background? That's parallax. When observing stars, astronomers consider the observed parallax as an angular measurement and plug it into the equation. From there, all that's left is to solve for X (the larger circle's radius, and the distance from Earth to the distant object). For the planets and some stars, it works great. As the distance to the observed object increases in proportion to the baseline (which cannot exceed the width of Earth, unless we're using some kind of wacky satellite array), the accuracy degrades.

What's the point of all this? Well, M31 has no parallax. This means that is very far away; somewhere behind pretty much every other visible object in the sky. This carried some profound and startling implications for 19th century astronomers: namely that it could not possibly be a star, a nova, a nascent solar system, or any other stellar object known to man at that time. If something that far away could still appear in the sky with the same angular (ie apparent) size of a small "local" star, it had to be unimaginably massive.

There were great debates in the early 20th century as to what M31 could possibly be. Thanks to perpetual improvements in observational technology, breakthroughs in the measurement of stellar distance, and many, many, many hours of observation and number crunching, astronomers concluded that M31 -- formerly known as the Andromeda Nebula -- was an entirely different galaxy; a stellar system existing trillions upon trillions of miles (something like 40,233,599,999,999,998 miles, to tack an actual number to it) beyond everything that astronomy had for thousands of years believed to represent the entirety of the cosmos. The realization that Andromeda was a galaxy was more or less the discovery of a new universe. This was some Silent Upon a Peak in Darien business times ten thousand.

So! That's what I saw in my binocular lenses last night. I'd seen Andromeda before in textbooks and on computer screens -- all very lovely pictures, all much clearer, crisper, and infinitely better looking than the dim grayish blob in my vision -- but this was my first time seeing the genuine article for myself. It was kind of incredible. The 2.51 million-year-old radiation from a trillion suns actually tickled my optic nerves. However briefly and however faintly, I was directly experiencing the distant touch of another cosmos.

I really do wonder why more people aren't into this stuff.

Fun fact: Whereas most of the cosmos is expanding away from Earth and the Milky Way, Andromeda is actually HURTLING TOWARD US.

(Image at the top ganked from Astro Nut.)

1 comment:

  1. How tiny and barren it is to think of 40 quadrilion miles of... not even air between that light and us, and yet I still know I'm not groking the void in nearly enough scale.