How Do Gravity and Orbital Motion Create Them?
At each Lagrange point, the combined gravitational effects and the smaller object’s orbital motion balance in a frame rotating with the two larger bodies.
At Sun–Earth L1, Earth’s gravity partly counters the Sun’s pull on a spacecraft between the two bodies. At L2, Earth’s gravity adds to the Sun’s pull, allowing a spacecraft farther from the Sun to keep pace with Earth.
What Makes the Five Points Different?
In the Sun–Earth system, L1, L2 and L3 lie along the line through the Sun and Earth. L4 and L5 sit 60 degrees ahead of and behind Earth in its orbit.
The points differ in stability.
In 2011, NASA reported that its WISE mission had confirmed 2010 TK7, the first known Trojan asteroid associated with Earth’s L4 point.
How Do Spacecraft Use Lagrange Points?
The Sun–Earth L1 point is about 1.5 million kilometres from Earth, towards the Sun. The SOHO spacecraft orbits around L1, where it has an uninterrupted view of the Sun.
The James Webb Space Telescope orbits around Sun–Earth L2, also about 1.5 million kilometres from Earth. From there, its sunshield blocks the Sun, Earth and Moon.
Do Spacecraft Sit Still at a Lagrange Point?
Spacecraft at Sun–Earth L1 and L2 usually travel in halo or Lissajous orbits around the points rather than remaining motionless on them.
L1, L2 and L3 are unstable, so a spacecraft near one of them needs occasional thruster corrections to remain nearby. NASA describes L1 and L2 as unstable on a timescale of about 23 days.
