Strong opinions, weakly held

Our place in the universe


I have no idea where this image illustrating the relative size of the Earth compared to other bodies in the universe came from, but it’s amazing.

I admit, I’m a total sucker for this sort of thing.


  1. Cool, but doesn’t appear to be totally accurate. VY Canis Majoris is in fact the largest known star at 2,100 solar radii. But that diagram shows Rigel at 62 solar radii being (much much) larger than the entire solar system, whereas 62 solar radii is still well inside the orbit of Mercury. So I don’t know how much I’d trust the other parts of the diagram based on that…

    Some numbers you can check with: Earth’s radius: 6,371 km Sun’s radius: 650,000 km Mercury’s orbital radius: ~50,000,000 km Rigel’s radius: 40,300,000 km Saturn’s orbital radius: ~1,400,000,000 km VY Canis Majoris’ radius: 1,365,000,000 km Uranus’ orbital radius: ~2,900,000,000 km

    What that really says is: the Earth is really big. The Sun is really, really big. Rigel is really really big compared to the Sun. VY Canis Majoris is really really big compared to Rigel. But VY Canis Majoris and our entire solar system are about the same size – it’s just that the Sun and planets are really tiny by comparison to the solar system.

  2. My favourite of those kinds of things is when SF books blithely talk about Galactic Empires, or how we “outgrew” the Milky Way and moved elsewhere.

    The MIlky Way contains at least 200 billion stars. That would be, say, 50 stars for each human being currently alive. OK, we have no idea what percentage of systems have planets, let alone Earthlike planets, but even if it’s 0.001% that would be two million Earths in our galaxy. Assume you can populate each one to half our current population; that’s a million times the current human population, or about 6 quadrillion people.

    You often read stories in which within one or two thousand years the entire galaxy is populated with humans. Quite aside from the speed-of-light problem (just getting to the other side without stopping would take 50 or 75 thousand years, let alone trying to settle along the way) – which is usually sidestepped by cheesy FTL – even at the incredibly fast growth rates of the last 300 years, human population only increased by 10x. So, it would take 600 years to get to 100x, 900 years to get to 1,000x, 1,200 years to get to 10,000x, 1,500 years to get to 100,000x, and 1,800 years to get to 1,000,000x. And if the percentage of Earthlike systems is 0.01% that increases the reproduction time by another 300 years, and so on. This also assumes that you can efficiently transport excess population from any planet to the empty ones, the way human beings did over the past 300 years. If you can’t, the geometric rate of increase would be much, much slower.

    Although if you’re assuming FTL you might as well assume cloning and robotic parenting and a load of other rubbish too, I suppose.

    Realistically, if we’ve sent a robotic probe to another nearby star within the next 100 years I would be pleasantly surprised. It seems fairly unlikely to me.

  3. Great post and follow up comments. I would love to see the above youtube clip in HD with some neat music.

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