What is Aditya-L1? India's mission to study the Sun, explained
By the WhyCosmos team · Last updated:
Aditya-L1 is India's first space-based observatory to study the Sun. Launched by ISRO on 2 September 2023 on PSLV-C57, it reached a halo orbit around the Sun-Earth Lagrange point 1 (L1), about 1.5 million km from Earth, on 6 January 2024. From there its seven instruments watch the Sun without interruption.
Ten days after Chandrayaan-3 landed on the Moon, ISRO launched a mission in a very different direction: towards the Sun. Aditya-L1 does not fly to the Sun or anywhere near it. It sits at a carefully chosen balance point where it can watch the Sun without interruption. This page explains where it is, what it measures, and why a solar observatory matters for life on Earth.
How to explain it to your child
Explain it to an 8-year-old
Think of Aditya-L1 as a science observatory parked far out in space, where it can keep watching the Sun all the time, day and night. It uses special instruments to study the Sun's light, its very hot outer layer, and the tiny particles that fly out from the Sun into space.
Explain it to a 13-year-old
Aditya-L1 is a solar observatory in a halo orbit around the Sun-Earth L1 point, a place where the pull of the Sun and Earth, combined with the spacecraft's motion, lets it keep pace with Earth as both go around the Sun. Four of its instruments look at different layers of the Sun; three measure the solar wind's particles and magnetic field directly as they stream past, helping scientists study solar activity and space weather.
Key facts
| What it is | India's first space-based mission to study the Sun |
|---|---|
| Launched | 2 September 2023, on PSLV-C57, from Sriharikota |
| Arrived at L1 | 6 January 2024 (halo orbit insertion) |
| Distance from Earth | About 1.5 million km, about 1 percent of the way to the Sun |
| First halo orbit completed | 2 July 2024, after 178 days |
| Instruments | Seven: four observe the Sun, three measure particles and magnetic fields |
| Name | Aditya is a Sanskrit name for the Sun; L1 is the Lagrange point |
| Project director | Nigar Shaji, ISRO |
What is the L1 point?
The L1 in Aditya-L1 stands for Lagrange point 1. Lagrange points are places in space where the gravity of two large bodies, here the Sun and Earth, balances with the motion of a smaller object so that it can hold its position relative to them. There are five such points for the Sun and Earth.
L1 lies about 1.5 million km from Earth, directly towards the Sun. That sounds far, but it is only about 1 percent of the 150 million km between Earth and the Sun. Aditya-L1 is in good company: the NASA-ESA SOHO observatory has watched the Sun from L1 since 1996, and the James Webb Space Telescope works at L2, on the opposite side of Earth.
Why is L1 a good place to study the Sun?
From L1 the Sun is never hidden by Earth or the Moon, so Aditya-L1 can watch it continuously, without the regular interruptions that satellites close to Earth experience. It also sits upstream in the solar wind, the stream of charged particles flowing out from the Sun, so its instruments sample that material before it reaches Earth's magnetic field, giving early warning of what is coming.
What are the seven instruments on Aditya-L1?
All seven payloads were developed in India, by ISRO centres and Indian research institutions.
| Instrument | What it studies | Developed by |
|---|---|---|
| VELC (Visible Emission Line Coronagraph) | The corona and coronal mass ejections | Indian Institute of Astrophysics, Bengaluru |
| SUIT (Solar Ultraviolet Imaging Telescope) | The photosphere and chromosphere in ultraviolet light | IUCAA, Pune |
| SoLEXS (Solar Low Energy X-ray Spectrometer) | Low-energy X-rays from solar flares | U R Rao Satellite Centre, Bengaluru |
| HEL1OS (High Energy L1 Orbiting X-ray Spectrometer) | High-energy X-rays from solar flares | U R Rao Satellite Centre, Bengaluru |
| ASPEX (Aditya Solar wind Particle Experiment) | Protons and heavier ions in the solar wind | Physical Research Laboratory, Ahmedabad |
| PAPA (Plasma Analyser Package for Aditya) | Electrons and ions in the solar wind | Space Physics Laboratory, VSSC, Thiruvananthapuram |
| Magnetometer | The magnetic field carried by the solar wind | Laboratory for Electro-Optic Systems, Bengaluru |
The first four look at the Sun (remote sensing); the last three measure their surroundings directly (in situ).
What are the photosphere, chromosphere and corona?
The photosphere is the bright visible surface of the Sun, at about 5,500°C. Above it lies the chromosphere, a thin layer best seen in particular colours of light. Farther out is the corona, the Sun's outer atmosphere, which is more than a million degrees, far hotter than the surface beneath it. Why the corona is so hot is one of the biggest open questions in solar physics, and one that Aditya-L1 is designed to help answer.
Normally the corona is visible only during a total solar eclipse. VELC carries its own eclipse: a coronagraph that blocks the Sun's bright disc so the corona can be studied every day.
Why do solar flares and coronal mass ejections matter on Earth?
A solar flare is a sudden burst of energy in the Sun's atmosphere, above sunspots. A coronal mass ejection, or CME, is a huge cloud of hot gas and magnetic field thrown out into space. When a strong one reaches Earth it can disturb satellites, GPS signals, radio communication and power grids, and it produces auroras.
In May 2024, the strongest geomagnetic storm in about two decades produced auroras photographed from Hanle in Ladakh, and ISRO reported that Aditya-L1's instruments had recorded the solar activity behind it. Modern life depends on satellites, so understanding these storms has real practical value.
Did Aditya-L1 go close to the Sun?
No. This is a common misconception. Aditya-L1 stays about 1.5 million km from Earth, while the Sun is about 150 million km away, so it is around a hundred times closer to Earth than to the Sun. It does not need to get close: its job is to watch, not to touch.
Why does a solar observatory carry ultraviolet and X-ray instruments? Because different layers of the Sun shine most strongly in different kinds of light. The electromagnetic spectrum, from radio waves to X-rays, is lesson 6 of Astronomy 201, the WhyCosmos course that follows Astronomy 101.
Questions parents and kids ask
Aditya-L1 is an Indian spacecraft that studies the Sun from a special point in space about 1.5 million km from Earth, where it can watch the Sun without interruption.
Aditya is a Sanskrit name for the Sun, and L1 refers to the Sun-Earth Lagrange point 1, the region of space where the spacecraft operates.
ISRO launched Aditya-L1 on 2 September 2023 on a PSLV-C57 rocket from the Satish Dhawan Space Centre, Sriharikota.
In a halo orbit around the Sun-Earth L1 point, about 1.5 million km from Earth, where it has operated since 6 January 2024. Each loop of its halo orbit takes about 178 days.
Nigar Shaji, an ISRO scientist, served as the project director of the Aditya-L1 mission.
It helps scientists understand how solar eruptions start and travel through space, and its instruments sample the solar wind before it reaches Earth. That knowledge improves space-weather science and forecasting.
Your child asks questions like this every week.WhyCosmos runs live online astronomy classes for ages 8–16, taught by real astrophysicists — where questions like these are the curriculum.
Related terms in this glossary
Sources and further reading
ISRO: Aditya-L1 · ISRO: Aditya-L1 completes its first halo orbit · NASA: What is a Lagrange point?