Science For Everyone: Why It Is Important To Study The Sun, And How Aditya-L1 Will Do So

Science For Everyone: This week, we discuss the importance of studying the Sun, how the star helps us, what knowledge we have about the solar system’s only star, and which mysteries still remain.

Sun: Welcome back to “Science For Everyone”, ABP Live’s weekly science column. Last week, we discussed all the successful lunar missions launched till date. As the Indian Space Research Organisation (ISRO) successfully launches Aditya-L1, India’s first space-based solar observatory to study the Sun, we discuss this week the importance of studying the Sun, how the star helps us, what knowledge we have about the solar system’s only star, and which mysteries still remain. Aditya-L1 aims to study the Sun from a special location in space, and is expected to make interesting scientific discoveries.

ISRO launched Aditya-L1 on September 2, 2023, at 11:50 am IST, from Satish Dhawan Space Centre, Sriharikota, Andhra Pradesh. Aditya-L1 was placed into the intended orbit over an hour after launch. The spacecraft is now in low-Earth orbit, and will perform orbit-raising manoeuvres to change its orbit from circular to elliptical. Aditya-L1 will reach its destination, which is a halo orbit around Lagrange point 1 (L1), in January 2024, about 125 days from launch.

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Why the Sun is so important

To say that the Sun is of immense significance would be an understatement. The only star in our solar system, the Sun holds all the planets in their orbits with its gravitational pull. The 4.5-billion-year-old star is the largest object in the solar system, a hot glowing ball of hydrogen and helium in which nuclear fusion reactions keep taking place, and the source of energy for all life forms. Without the Sun, life would cease to exist on Earth as temperatures will plummet to extremely low levels. Plants use only about one per cent of the Sun’s energy to carry out photosynthesis, and reflect off the rest of the wavelengths.

The Sun is responsible for days and nights, determined by whether a particular side of the Earth faces the star or not. Since the Earth revolves around the Sun, the star is also responsible for seasons. It drives weather as well as climate.

Earth’s host star also releases high-energy particles, magnetic fields, and large amounts of energy, all of which influence the space weather of not only the Earth, but also of all the planets in the solar system. 

In short, the Sun is the ultimate source of heat, light, and energy for Earth.

How knowledge about the Sun evolved over the years

People started gaining knowledge about the Sun over 3,000 years ago. It may come as a surprise to many that the oldest record of a solar eclipse dates back to 1223 BC. In 800 BC, the first sunspot observation was recorded. This refers to a dark spot on the surface of the Sun that disappears after appearing for a few days or weeks. 

In 200 BC, Aristarchus of Samos made the first attempt to determine the Sun-Earth distance using mathematics. 

Leo Diaconus, an ancient historian, was the first to explicitly mention the corona. Describing a solar eclipse in 968 AD, he wrote, "And it was possible to see the disk of the Sun, dull and unlit, and a dim and feeble glow like a narrow band shining in a circle around the edge of the disk".

In 1610, four astronomers — Johann Goldsmid, Thomas Harriot, Galileo Galilei, and Christoph Scheiner — simultaneously but separately made the first telescope observations of sunspots. The oldest recorded sunspot observation was made by Harriot.

Polymath Nicolaus Copernicus devised a system which replaced the Earth with the Sun as the centre of the universe. While the Copernican system did maintain a distinction between the Sun and fixed stars, it mentioned that the fixed stars were located along the outermost sphere of the cosmos. Several astronomers rejected this theory, René Descartes being one of them. He wrote in his 1644 book that the Sun is one of many stars, and each of these stars is formed at the centre of a vortex. 

Thus, in 1644, the Sun was seen as a star for the first time.

In 1687, Isaac Newton gave the first quantitative estimate of the Sun’s mass.

Over the years, scientists obtained more knowledge about the Sun. In 1817, solar spectroscopy was born due to the efforts of Joseph von Fraunhofer, who rediscovered dark lines in the solar spectrum. 

In 1845, French physicists Louis Fizeau and Léon Foucault obtained the first solar photograph. In 1859, astronomer Richard C Carrington made the first observation of a solar flare. The first observations of coronal mass ejections were made in 1860, after scientists thoroughly studied the total solar eclipse of July 18, 1860.

Why it is important to know more about the Sun

Studying the Sun, which is the largest object in the solar system, and the nearest star to Earth, can help scientists understand more about other stars in the Milky Way galaxy, and about stellar objects in other galaxies. A multitude of eruptive phenomena occur in the Sun. While the Sun is the source of energy for all life forms, the release of excessive energy towards Earth results in disturbances in the near-Earth space environment. 

For instance, these disturbances disrupt communication systems and damage spacecraft. Also, astronauts are sometimes in danger of being exposed to explosive solar phenomena. Therefore, understanding solar dynamics will allow scientists to devise systems that will ensure early warning of eruptive events. 

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Inside the 4.5-billion-year-old star, nuclear fusion reactions occur. Aditya-L1's findings may help scientists understand these reactions better, and how they power the Sun. The temperature of the central region of the Sun, or the core, is about 15 million degrees Celsius, and that of the photosphere is about 5,500 degrees Celsius. Aditya-L1 will also study the reasons behind this difference in temperature. 

Thermal and magnetic phenomena keep occurring inside the Sun, and hence, the star serves as the perfect natural laboratory to understand certain occurrences that cannot be explained in the laboratory. 

How Aditya-L1 will help scientists understand space weather

The Sun emits radiation, heat energy, magnetic fields and particles. A solar wind refers to the constant flow of particles from the Sun. These particles are mostly high-energy protons. Most of the space in the solar system is filled with solar winds and solar magnetic fields. 

Space weather is affected by solar winds, solar magnetic fields, and explosive solar events such as coronal mass ejections. 

These eruptive phenomena change the nature of Earth's magnetic field, and also the charged particle environment. When Earth's magnetic field interacts with coronal mass ejections, a magnetic disturbance occurs near the planet, affecting the working of satellites and communication systems. 

Therefore, by studying the changing environmental conditions in space, Aditya-L1 can provide insights into how solar activities impact space weather in real time.

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It is important to study the Sun because being the nearest star to Earth, it can be studied more easily than other stars. Also, the world can learn more about other stars in the Milky Way galaxy, and stars in other galaxies, by understanding the dynamics of the Sun well.

Another reason why it is important to study the Sun is that scientists are yet to have a deep understanding of space weather, which is a term used to describe changing environmental conditions in space.

Eruptive phenomena such as coronal mass ejections, solar winds, and high-energy magnetic fields from the Sun cause disturbances in the near-Earth environment when they are directed towards the planet, and hinder the working of spacecraft and communication systems. Moreover, explosive solar phenomena can be detrimental to the health of astronauts if they are exposed to high-energy radiation. 

Solar winds, which refer to the high-energy particles released by the Sun, fill most of the space in the known solar system. These high-energy particles are mostly high-energy protons. 

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Not only does the Sun emit high-energy particles, but also magnetic fields and plasma, eruptions of which are known as coronal mass ejections. 

The charged particle environment and the nature of magnetic fields near the Earth change when particles and magnetic fields from the Sun are directed towards the planet. Since these explosive phenomena can affect space assets, it is essential to send spacecraft that will perform experiments to understand the impact of solar activities on space weather in real time. Aditya-L1 is one such solar mission. 

Most importantly, the Sun serves as a natural laboratory to understand nuclear fusion reactions, and different thermal and magnetic phenomena, which can otherwise not be simulated on Earth.  

Therefore, a better understanding of these phenomena will help scientists devise early warning systems to ensure that corrective measures can be taken in advance. 

While the Sun emits radiation in nearly all wavelengths, together with high-energy particles and magnetic fields, Earth's atmosphere and magnetosphere together serve as a protective shield against solar radiation. Since Earth's atmosphere and magnetosphere block radiation of harmful wavelengths, and high-energy particles and fields, these do not reach the surface of the planet. As a result, Earth-based solar observatories are unable to detect these radiations, and scientists are unable to conduct studies based on these phenomena. 

But, if an observatory is placed in space, it can make observations from outside the Earth's atmosphere, and conduct solar studies. 

Aditya-L1 is an observatory which will study solar wind particles and magnetic fields emitted by the Sun from a strategic location far away from the influence of Earth's magnetic field, make measurements of different phenomena, and try to understand how these events travel through interplanetary space and shape the conditions there. 

While Aditya-L1 is not a complete mission to study the Sun, its scientific payloads are capable of carrying out measurements to understand the invitation of coronal mass ejections and solar flares, the distribution of solar wind anisotropy, the mechanisms of coronal heating and acceleration of solar winds, and the dynamics of the solar atmosphere. 

In the future, more space-based solar observatories will be developed to understand the distribution of energies of explosive solar phenomena in different directions, and study the polar regions of the Sun.