The Sun, and how it has fuelled humanity’s curiosity, knowledge
The Indian Space Research Organisation (ISRO) is launching the Aditya-L1 mission to study the physics and chemistry around the Sun.
In Jules Verne’s classic Around the World in Eighty Days, the Sun can be said to be one of the central figures. Phileas Fogg and his fellow travellers see the Sun rise and set 80 times during their round trip from west to east, and therefore presume that 80 days and nights must have elapsed. It takes Fogg a little bit of arithmetic to correct one of literature’s most famous miscalculations and collect his bet in the nick of time the following day. Travelling in that direction and seeing 80 sunrises and 80 sunsets, as he works out, could only have meant that 79 days had elapsed.
The Sun, the source of all energy that sustains life on Earth, has inspired knowledge for as long as humanity has existed. Isro’s Aditya-L1 mission, launching on Saturday, seeks to add to our knowledge about the physics and chemistry at play around the Sun, concepts that are far more complex than the arithmetic in Verne’s novel. Fogg’s correction can be explained either with longitudes (as Verne did) or simply with the relative motion between two objects charting the same circular path in opposite directions.
Even that, however, would be far more advanced than the knowledge of the ancients who believed the Earth was flat.
Growth of knowledge
Much of our early knowledge, particularly of geometry, trigonometry and astronomy, is a result of a curiosity to understand the motion and the influence of the heavenly bodies. While their mathematical observations were remarkable given the constraints of their times, many early scholars also dwelt on the supposed astrological influence of the heavenly bodies, which has no connection with what modern science has taught us.
The accumulation of knowledge would have started with the obvious observation that the Sun gives us days and nights. Deification was inevitable; countless civilisations have had countless sun gods, and indeed Sun-worshippers exist even today.
Eclipses captivated scholars early on, with the earliest known records (in Ugarit, now in Syria) dating back more than three millennia ago. Eventually, eclipses would inspire calculations that would establish the Earth as round, and also attempts to determine the Sun’s distance from our planet. Early models of the Earth-Sun system, however, placed the Earth at the centre of the universe, with other heavenly bodies including the Sun revolving around the planet.
The modern model of the Solar System arose out of the work of Copernicus in the 16th century, and improved on by Kepler in the 17th. This model placed the Sun at the centre, with the planets including Earth (which spins on its axis) orbiting their star while the Moon orbits the Earth. A millennium before Copernicus and Kepler, incidentally, Aryabhata of India had correctly proposed that the Earth spins on its axis, although he had placed the Earth at the centre of the Universe.
Celebrated scientists weighed in on Copernicus and Kepler’s work. Galileo’s telescopes enabled closer observations of the Sun, including sunspots; Descartes described the Sun as one of many stars (unlike Copernicus and Kepler who had thought it distinct); and Newton’s mathematics provided a reasonably accurate estimate of the mass of the Sun.
Later advancements included solar spectroscopy, knowledge that the Sun rotates at differential rates and therefore must be made of fluid in the outer layers, and about the Sun’s chemical composition, its magnetic nature and solar flares, which are bursts of radiation ejected from the ball of fire.
What more to learn
We know today that the Sun is made of plasma, which is a super-ionised gas that is moving constantly. Energy from the Sun, created as a result of nuclear fusion reactions, reaches us through light or bursts of magnetism or particles. These can influence the space environment, and missions probing the Sun seek to understand the ways in which that can happen.
NASA has several solar missions include the Parker Probe, while The European Space agency has a solar orbiter. NASA lists several reasons for studying the Sun: the influence of its radiation that can be either a boon or hazard for life on Earth; its influence on space weather, space technology and communications systems; and the fact that it is the only star we can study up close, learning more about other stars in the process.
Isro’s Aditya-L1 mission too will study radiation and its influence on space weather and space infrastructure. It will be in halo orbit around a point called L1, 1.5 million kilometres from Earth, chosen because it offers observations without hindrance from phenomena such as eclipses.
“Various spacecraft and communication systems are prone to such disturbances and therefore an early warning of such events is important for taking corrective measures beforehand. In addition to these, if an astronaut is directly exposed to such explosive phenomena, he/she would be in danger,” a booklet on the mission says.
“Thus, the Sun also provides a good natural laboratory to understand those phenomena which cannot be directly studied in the lab.”