Aditya-L1: India's first mission to study the Sun

The Sun is the basis of life on Earth, but its storms can also threaten our satellites in space. To watch and understand the Sun without a break, ISRO sent Aditya-L1 — India's first space-based solar observatory. "Aditya" is a Sanskrit name for the Sun, and "L1" is the name of the special place where the craft is stationed.

Aditya-L1 at a glance

What is the L1 point?

Between the Sun and Earth there are five places where the pull of their gravity balances in such a way that a small craft can stay in position using very little fuel. They are called "Lagrange points", after the mathematician Joseph-Louis Lagrange. Of these, L1 lies about 1.5 million kilometres from Earth, towards the Sun. From there the Sun is always visible — neither Earth nor the Moon gets in the way — so there is never an eclipse. Aditya-L1 moves around this point in a "halo orbit".

Did you know? 1.5 million kilometres is only about 1% of the distance between Earth and the Sun, yet it is nearly four times the distance from Earth to the Moon (about 384,000 kilometres).

The journey to L1

After launch, Aditya-L1 circled Earth for a few days, and its engine was fired four times to raise its orbit. On 19 September 2023, with one big push, it left Earth's sphere of influence and set off towards L1. After a journey of about four months, on 6 January 2024, it was placed in the halo orbit around L1. It was ISRO's first mission to a Lagrange point, and most of its instruments were built by India's own scientific institutions.

A few facts about the Sun

• The Sun's diameter is about 109 times that of Earth.
• Sunlight takes about 8 minutes and 20 seconds to reach us.
• The Sun is a star made mostly of hydrogen and helium, and it shines by nuclear fusion in its core.

Aditya-L1's seven instruments

• VELC: the largest instrument, which studies the Sun's outer atmosphere, the "corona" (built by the Indian Institute of Astrophysics, Bengaluru).
• SUIT: takes pictures of the Sun in ultraviolet light (IUCAA, Pune).
• SoLEXS and HEL1OS: measure the X-rays given off by solar flares.
• ASPEX and PAPA: study the particles of the "solar wind" coming from the Sun.
• Magnetometer: measures the magnetic field at L1.

Why study the Sun?

From time to time the Sun throws out powerful flares and "coronal mass ejections" (CMEs) — huge clouds of charged particles. When these head towards Earth, they can disturb satellites, GPS, radio communication and power grids. This is called "space weather". Aditya-L1 can see these particles before they reach Earth, which helps in giving warnings. Aditya-L1's instruments also recorded the big solar storm of May 2024.

There is a great mystery too: the Sun's surface is about 5,500 °C, yet the corona outside it is millions of degrees hot. Understanding why is another aim of the mission. Read about events involving the Sun and the Moon in How eclipses happen, and about India's festival of Sun worship in Interesting facts about Chhath Puja.

ISRO's other missions: ISRO's major missions · More articles: Science · Science questions.