Guntur, spectral lines, and the discovery of helium

Did you know that helium is the first alien element, so as to say? This means that its existence elsewhere was discerned much before it was actually discovered here on our planet. A.S.Ganesh traces back to Guntur on August 18, 1868 to tell you this story…

What on Earth does a gas that we normally associate with balloons have to do with Guntur, a city in Andhra Pradesh? Everything, apparently! Though, to be absolutely clear, it must be stated that it all started with observations of the sun from Guntur, before the existence of helium on Earth was ever discovered.

Making up nearly a quarter of all matter in the universe, helium is the second-most abundant element in the cosmos, behind only hydrogen. Despite this, helium is rather rare on Earth, only given off as a product when heavier elements undergo radioactive decay. Unless it is produced deep underground or trapped within rocks, the ultra-light non-reactive helium usually flies off and vanishes into space.

The story of the discovery of helium is a long, drawn-out one that spans the major part of an entire century. While the Guntur episode is an important one, it comes somewhere in the middle of the entire story. To begin with, we would have to step back over two centuries to 1814.

A lot of information regarding a substance and its structure can be arrived at by studying the light absorbed or emitted by it. With their ability to disperse light into measurable wavelengths, spectroscopes were about to change the way scientists studied the chemical composition of nearly everything.

Using an early version of a spectroscope, German optical lens manufacturer and physicist Joseph von Fraunhofer created a spectrum broad enough to notice dark black lines interrupting the normal colours. While he didn’t understand what they were, they now bear his name (Fraunhofer lines) and it set the ball rolling with regard to studying spectral lines to better understand substances.

By 1859, Germans Gustav Kirchhoff and Robert Bunsen mastered the art of using the analyses of light to figure out the chemical composition of the sun and the stars. The physician-chemist duo, credited with the invention of the modern spectroscope as we know it today, discovered that elements produced bright lines of light in the spectroscope when heated, and that these lines sometimes corresponded to the Fraunhofer lines.

With the understanding prevalent then suggesting that the sun’s spectrum could only be observed during an eclipse, astronomers were eagerly awaiting the total eclipse predicted for 1868. As the eclipse was to have nearly six minutes of totality – a long time in the context – it afforded plenty of observational time. The path of totality passed through the breadth of India, forcing the scientific community world-over to make a beeline for the country.