Lagrange points are five places near two large bodies, like the Sun and Earth, where a small spacecraft can keep the same position relative to both.
Normally, anything closer to the Sun than Earth goes round it faster than Earth does. But there are special spots where the pulls of the Sun and Earth, together with the spacecraft's motion, balance out. A spacecraft placed there keeps pace with Earth. These are Lagrange points, named after the mathematician Joseph-Louis Lagrange (1736–1813).
Every pair of large bodies has five of them, labelled L1 to L5. Spacecraft placed at or near them need less fuel to hold their position than they would almost anywhere else.
L1, L2 and L3 are unstable: a spacecraft there slowly drifts away, on a timescale of about 23 days for L1 and L2, so it needs regular small corrections. L4 and L5 are stable, and natural objects collect there; these are called Trojans.
Aditya-L1, India's solar observatory, launched on PSLV-C57 from Sriharikota on 2 September 2023. It reached a looping halo-orbit around the Sun–Earth L1 point on 6 January 2024.
ISRO chose L1 because the spacecraft can watch the Sun without interruption and stays outside Earth's magnetic bubble, the magnetosphere, so it can sample the solar wind directly. The SOHO solar observatory works from the same point. The far side, L2, hosts telescopes that want to look away from the Sun, such as the James Webb Space Telescope.
Aditya-L1 does not appear on this site's globe. The orbit models the tracker uses are built for satellites circling Earth, so its mission page tells its story instead.
The mission timeline shows Aditya-L1's journey from launch on 2 September 2023 to its halo orbit around L1 in January 2024. Follow Aditya-L1
For a small body near a planet of mass m orbiting a star of mass M at distance R, the L1 and L2 points lie at roughly
r ≈ R · (m / 3M)^(1/3)
from the planet. The idea: at L1 Earth's pull partly cancels the Sun's, so the spacecraft feels a weaker net pull towards the Sun. A weaker pull means a slower orbit, and at exactly the right distance that slower orbit takes one year — the same as Earth's.
Worked numbers, using GM values instead of masses (the ratio is the same):
This matches the 1.5 million km quoted by ESA and ISRO, and shows where the "1% of the way to the Sun" comes from.
L4 and L5 are different. They sit at the corners of equilateral triangles with the Sun and Earth, and they are stable as long as the bigger body is more than 24.96 times as massive as the smaller one. The Sun–Earth and Earth–Moon pairs both pass easily. Natural objects collect there: they are called Trojans, and hundreds are known around Jupiter's L4 and L5.
From there it can view the Sun continuously, and it lies outside Earth's magnetosphere, so it can sample the solar wind directly.
L4 and L5. L1, L2 and L3 are unstable, so spacecraft there need regular station-keeping.
About 1.5 million km, about 1% of the Earth–Sun distance.