The James Webb telescope will not orbit the earth, instead it will orbit the sun. Imagine drawing a straight line from the sun to the earth and then extending this line by 1.5 million kilometers. This is the L2 Lagrange point. Just as the earth orbits the sun in ≈ 365 days, the James Webb telescope will also orbit the sun in ≈365 days. What this means is that at the L2 Lagrange point, the earth will always be between the telescope and the sun. And the distance between the earth and telescope wil