End of the world. Enjoy!

I was watching a show on the History channel the other night and sent my son a note about it.


My note to Daniel:

"Have you seen anything about the end of the world happening on 12/21/12 as predicted by the Mayan calendar? I'm watching it on the history channel. It talks about how Merlin's predictions, other oracle's prediction, Mayan calendar and something called software "bots" have all predicted that the earth will end on the same day. . . . It's interesting stuff. The way the earth is supposed to end is when the sun, Earth and a black hole align. The black hole was predicted in the Mayan calendar and just recently discovered in the middle of the Milky Way. It's fascinating if you listen to it as just a historical program, but kind of gives you the heebie jeebies if you start internalizing it all.


Daniel's awesome response to me:


I guess we'll find out in a few years.


The supermassive black hole at the center of the galaxy is called Sagittarius A* (pronounced "a star"). It is about 25,900 lightyears from Earth. It has a mass of about 3.7 million suns. The acceleration due to gravity of an object is:


g = -mG/r^2
where g = the acceleration due to gravity
m = the mass of the object
G = the gravitational constant
r = the distance to the object


Plug in the numbers for Sag A* into that equation, and you get an acceleration due to gravity of -8.179e-15 m/s/s.


Jupiter, on the other hand, is much smaller, but much closer. It has a mass of 1.8986e27 kg and it is located 4.204 AU from Earth. Plugging in those numbers, and we get -3.202e-7 m/s/s. That means that the average pull on Earth by Jupiter is 8 orders of magnitude stronger than Sag A*.


I would be far more worried about the gravitational effects of Jupiter than any black hole at the center of the galaxy. But we align between Jupiter and the Sun at least once a year, yet the Earth hasn't exploded.


By far the densest object Earth encounters every year is Congress. Now that might be something to
worry about.


Daniel.