No fear of 2012, Part 2

In No fear of 2012, Part 1, I started discussing one of the scenarios I've heard, giving supposed astronomical reasons why the world will end in 2012.

Here's another that a student brought up recently: Will the planets line up perfectly in 2012, causing disaster for Earth?

Well... no. Actually, make that definitely not.

Follow up:

1) We know the orbits of the planets to a rather high precision - which is how we can send missions to Mars or Pluto years before the planet will actually get to the targeted location. Because those orbits have slight tilts to each other, it is in fact impossible to ever get them all in an exactly straight line. But even if you allow for very wide approximation, there will be no time in 2012 in which all, or even most, of the planets will lie on anything resembling a line. Check it for yourself here.

2) Even if many planets COULD lie along a straight line - so what? If you're thinking of all the gravity of all the planets adding up to cause trouble - nope. The planets are just too small and too far away to have a catastrophic gravitational effect on Earth, even if they all acted together. To give you some idea, 99.9% of all the mass in the solar system is in our Sun. All of the planets put together make up less than 0.1% of the Sun's mass. Compared to the Sun, it would be like a 300-pound wrestler pulling on one of your arms and seven butterflies on the other arm - who's gonna win? In addition, the planets are far away from us, and gravity drops off rapidly with increasing distance. To have any catastrophic effect, the planets would have to be much closer to us than they ever get in their orbits. (See #1.)

3) Usually, what people mean when they say "planetary alignment" is that many or most or the planets are seen in the same part of the sky. (That does not involve the planets actually lining up in space - they just look like they're lined up in our sky in what's called a conjunction.) What's really happening there is that all planets are roughly on the same side of the Sun, and that happens every two centuries or so. We've never noticed any unusual effects from such an arrangement. At no time in 2012 will we see a conjunction of all seven planets in our sky - use the planetarium program of your choice to check this.

For a more extensive account - with math - see this link, written the last time this scare was being passed around in 2000. Notice that nothing happened in 2000...

Click here for No fear of 2012, Part 3.