Force map of the Lagrange points

[jaufrec]

<img src="http://map.gsfc.nasa.gov/m_ig/990529/990529b.jpg" alt="picture of lagrange forces">
<p>The Lagrange points are places between two heavenly bodies where small objects can orbit stably. <b>L1</b>, <b>L2</b>, and <b>L3</b> are stable but precarious, and any random bump (like solar wind or the influence of the other planets) can dislodge you. But <b>L4</b> and <b>L5</b> are <b>metastable</b> - if you get close, you'll get gently sucked in and you'll stay put. There are actually clusters of asteriods at the L4/L5 points of the Sun/Jupiter system. <p>Looking at this picture I thought I understood why 1-3 are stable and 4-5 aren't - 1-3 are at "saddles" whereas 4 and 5 are in depressions. But reading the <b><a href="http://map.gsfc.nasa.gov/m_mm/ob_techorbit1.html">text on the page</a></b>, it's even weirder. 4 and 5 really are hills - any bump and you should start to slide away. But in 4 and 5, Coriolis force pushes you back. That's the force that works in orbit like this (I think): going up makes you slower, going slower makes you go down, going down makes you go faster, going faster makes you go up. If you think that's confusing, well, orbital mechanics isn't rocket science; it's harder.