Entry 956, on 2009-03-02 at 20:24:30 (Rating 1, Science)
A few days back I blogged about how what we know about astronomy has changed over the last 30 years. Today I heard a podcast about the latest measurements of the Milky Way galaxy, which is the one we live in, and how our estimate of its size has changed. Our galaxy is part of a small group with one other large member, the Andromeda Galaxy. Previously we thought that Andromeda was bigger than the Milky Way but now it turns out that the two galaxies are about the same size.
So what, you may ask. Does that really matter? Well it doesn't really, but the thing that intrigued me was the accuracy of the measurements necessary to establish the new size estimates. Its much harder to measure the mass of the galaxy you are part of because of how much of it is blocked by gas and dust, but new radio measurements have been more accurate than anything previously achieved.
The measurements were made with the Very Long Baseline Array radio telescope which is effectively as big as the Earth! In reality it is a series of connected telescopes in different parts of the planet which work together to give the effect of one planet-sized telescope. The accuracy is 10 micro arc seconds!
If you aren't into astronomy that might not mean anything but imagine being able to read a road sign on the Moon! Or its the same as measuring the width of a human hair 2000 kilometers away, or measuring the width of a coin at a distance equivalent to 10 times the distance around the Earth! I think you will agree that is impressive accuracy!
A side effect of the greater mass of the Milky Way is that it will collide with Andromeda in a lesser time than we previously thought. The original estimate was in 5 billion years but it now seems that it will be less than that - I'm not sure how much less but its not something we need to worry about for a while!
One of the reasons I like astronomy is the way it casually discusses huge numbers, incredible stretches of time, and monumental concepts. Talking about measuring the size and predicting the future of galaxies containing hundreds of billions of stars (and probably even more planets, many of which might support life) is no exception.
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