The Milky Way

I had a late night chat with a friend (if 2.30 am is late enough for you). We chatted on myriad topics, ranging from a literary review of Suketu Mehta's award winning book, Maximum City to weird geometric object called fractals.

One particular topic which singularly set the discussion on fire was about our galaxy, the Milky Way. From childhood, we have been taught and found in textbooks that our galaxy looks something like this when seen from the top. I asked him like how did they arrive at this. I assume that nobody would have peeped out and seen how it looked like. Intuitively, exploring the structure of other galaxies seems to be much easier than doing that for our own galaxy.

However, my friend did have a reply which I found quite interesting. He said that we realized that planet earth was spherical long before we ventured out in outer space. I said that there is a rather simple explanation for that. When you stand on a coastline and see a ship approaching you, you first see the top of the mast followed by the sails followed by the complete ship. Also, this is true for all directions at any point on Earth. If that distance is measured, using some trigonometry the curvature of Earth can be found out.

He said that somebody must have done an analogous experiment for the Milky Way. However, we couldn’t think further. Can you help us?

Note: Neither of us is an astronomer, nor has had any formal study of it. We are just lowly Computer Science grads ;). But knowing about the cosmos is not the primary motive here. It is all about challenging the assumptions/half-truths rather than accepting them blindly, and to prove or disprove them for yourself. I feel that true understanding can come only through this way. My friend put it more beautifully. He said that this path is something even bigger than that. It is a path to enlightenment.