Helium And Its Discovery

On August 18th 1868, humanity made another great step in the quest of unlocking the secrets of the Universe: the discovery of helium. It happened during a Solar eclipse, in India.

Helium is one of the foundational elements of the Universe. It is the second most abundant element in the observable Universe, and the second lightest one too. This is why balloons are filled with helium. Where and when did we see helium the first time? When studying the Solar spectrum, in 1868.

How is helium created?

Most of the helium was created at the beginning of time, back when the big explosion which we now call the “Big Bang” happened. It was formed in the primordial nucleosynthesis, which is the process in which the first nuclei other than the lightest isotope of hydrogen were produced. It is believed by most cosmologists to have happened in the interval from 10 seconds to 20 minutes after the Big Bang.

Image result for helium spectral lines
The spectrum of Helium

The other way helium is created is nuclear fusion of hydrogen in stars. Most of the stars, like our Sun, generate their energy by the fusion of hydrogen into oxygen. Our Sun contains hydrogen, in a percent of 75%, and helium, 25%. As it is not an element we meet on Earth, it is obvious that the first place we will see it would be the Sun.

I have obtained one of the finest and least expected results - spectra of the stars! - and beautiful spectra with colors and magnificent lines. Just one more step, and the chemical composition of the Universe will be revealed.

The discovery

On August 18th, 1868, Pierre Janssen became the first person to observe helium. He didn’t even know it. All he knew was that it was something new.

Pierre Janssen

In the 1800s, scientists were just using a new instrument, called spectroscopes. A spectrometer produces spectral lines, which are later studied in order to find wavelengths and intensities of photons. From these analysis, chemical compositions are deduced.

On this day in August, Pierre Jules Janssen discovered a bright yellow line in the Sun’s spectrum, at a wavelength of 587,5 nanometers. The french astronomer, which was already famous for his dedication and his long roads for finding good viewing spots, camped in Guntoor, India, to watch as the Moon passed in front of the Sun, revealing Sun’s prominences. He observed that the yellow line, which everyone thought to be sodium, didn’t match with the wavelength of any known element. And so, even helium’s characteristics were almost similar to sodium’s ones, there were enough differences to make a different element, named later “helium”, after its discovery in the Sun (also named Helios).

Related: Why spectrum is the most important tool to study Astrophysics

The Spectrum of Hydrogen vs Helium

The first extraterrestrial element

As it is in every new shocking discovery in science, there has been a great deal of skepticism at first. It was hard for everybody to believe that there could exist any other elements other than those found on Earth.

I think here comes one of the great merits of Pierre Janssen. The main characteristic of scientists is to be open to new ideas. Janssen, in a world full of skeptics of his new weird idea, went on, culminating with helium being generally seen as a new element.

Helium was spotted for the first time on Earth in 1882. It happened during an analysis of the lava from Mount Vesuvius. That was the time Janssen’s discovery had been first acknowledged and its importance realised. Despite the skeptics, there were a lot of people who were believing and supporting Janssen without any doubt. One of them was the great astronomer, John William Draper. 

Also Read: The spectral classification of stars into 7 categories

Spectral lines and the spectroscope

In the 1800s, the spectroscope was very popular, and a hard instrument it. Joseph Frauenhofer first studied the Sun with the spectroscope. But, he was soon disappointed by the dark lines he saw, but did not understand. In the 1860s, two German scientists, Gustav Kirchhoff and Robert Bunsen realised that when heating different elements, they were producing different lines in the spectroscope. That was the moment some connection had been made between elements and the spectroscope. So after studying more elements and their image through the spectroscope, scientists were able to spot the differences between elements by how much they needed to be heated in order to produce a certain line on the image. So the two scientists discovered that every element produces a different spectrum.


Janssen was completely aware of the importance of his discovery. But even when knowing what he had done, he didn’t stop. Taking his passion in astronomy further, he developed a method for observing the Sun during the day. He travelled to India, Japan, Peru, and lots of other places just to get better observing sites. He did whatever it took to better understand the Universe. And somehow, that is the main reason we should keep him in mind, even after more than 150 years. The time was coming for the discovery to be made, and maybe more than the actual realisation, what we need to learn is to appreciate the Universe as he did. And to do whatever we do, not driven by the final achievement, but by the love for the subject we are willing to pursue.

Also Read: All the 30 articles of Basics of Astrophysics series

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