Astronomical fun facts

The sun doesn't rise in the east.  It actually doesn't rise at all; the earth rotates.  It can be difficult to remember this when watching it from the surface of the Earth, but doing so can really help change one's focus.

The space station is about 200 miles above Earth's surface.  If you could drive vertically as easily as you could drive horizontally, it'd take you about 3 hours (at normal 65 mph) to get there.  If you then decided to drive off to the moon, pack a few snacks: it'll take you another 6 months.

99.86% of the mass of the solar system is in the sun.  Jupiter is less than 0.1% of the mass of the solar system, yet it's 2.5x the mass of all the other planets combined.  That means that there's enough non-planetary mass in the solar system to make up 21 Earths.  Might get a little crowded around here.

The mass of the solar system is about 1.989x10^30 kilograms.  There are 6.022 protons and/or neutrons in 1 gram, or about 6,022 in a kilogram.  That means, in the solar system, there are approximately 12,000,000,000,000,000,000,000,000,000,000,000 protons or neutrons (electron mass is mostly insignificant).  This is off slightly, since some of that mass is converted to energy.

Contrary to popular belief, the Moon doesn't orbit the Earth: they both technically orbit a common gravitational "locus", similar to the way two people holding hands and spinning orbit some point between them.  Because the Earth has significantly more mass, the locus is "within" the Earth - a few thousand miles off-center, about 1000 miles below the surface - so, from a distance, Earth looks like it wobbles around its axis.  Also, the Earth - and all the planets - don't actually orbit the sun for the same reasons.  In fact, because of the distances involved and the density of the sun, the locus of Jupiter (also called the center of mass) is generally 30,000 miles above the surface of the sun, though the "wobble" of the sun changes dramatically depending on planetary alignment.

The milky way (our galaxy) is about 100,000 lightyears across and 1,000 lightyears thick.  This tells us that the volume of space it occupies is roughly 7.8 trillion cubic lightyears.  If we assume the high-end estimate of 400 billion stars, that means there are an average of 1 star per 19 cubic lightyears.  This isn't really accurate, since stellar density is far higher in the center of the galaxy than at the edges; out by us, the actual density is closer to 2300 cubic lightyears per star.

If we assume that radio waves have been broadcasting from Earth in some form since around 1880, then those signals fill a volume of space of approximately 9.2 million cubic lightyears.  That means our radio broadcasts have reached less than 4,000 stars and just over 0.0001% of the galaxy.  Needless to say, the odds that any of the planets near us could support life, much less *do* support life that could notice our broadcasts, is pretty low, but we've only just scratched the surface of the galaxy as a whole.

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