Discovery of Helium by Pierre Janssen on August 18, 1868

On August 18, 1868, French astronomer Pierre Janssen made a groundbreaking discovery during a total solar eclipse in Guntur, India. This event marked a significant milestone in the field of astronomy and chemistry, as Janssen identified a new element, helium, in the solar spectrum.

Context and Background

During the 19th century, the study of the sun and its composition was a major focus for astronomers. The use of spectroscopy, a technique that analyzes the light spectrum emitted by celestial bodies, had become a powerful tool for understanding the chemical makeup of stars. Prior to Janssen’s discovery, the elements known to science were primarily those found on Earth.

The Discovery

Pierre Janssen traveled to Guntur, India, to observe the total solar eclipse on August 18, 1868. Utilizing a spectroscope, Janssen observed the solar chromosphere and noticed a bright yellow line in the spectrum. This line did not correspond to any known elements at the time. Janssen’s observations were meticulous, and he concluded that this line indicated the presence of a new element in the sun.

Independent Confirmation

Remarkably, Janssen’s discovery was independently confirmed by English astronomer Joseph Norman Lockyer just a few months later. Lockyer observed the same spectral line and, together with chemist Edward Frankland, named the new element “helium,” derived from “Helios,” the Greek word for the sun.

Significance and Aftermath

The discovery of helium was significant for several reasons:

1. New Element: Helium was the first element to be discovered in space before being found on Earth, highlighting the potential of spectroscopy in astronomical research.

2. Advancement in Spectroscopy: Janssen’s work demonstrated the power of spectroscopic techniques in identifying elements and understanding the composition of celestial bodies.

3. Scientific Collaboration: The simultaneous discovery by Janssen and Lockyer underscored the importance of international collaboration and verification in scientific research.

Helium was not isolated on Earth until 1895 by chemists Sir William Ramsay, Per Teodor Cleve, and Nils Abraham Langlet, further cementing its place in the periodic table.

Broader Historical Impact

The identification of helium expanded the understanding of the universe’s composition and paved the way for future discoveries in both astronomy and chemistry. It also exemplified the interconnectedness of scientific disciplines and the global nature of scientific inquiry.

Janssen’s discovery remains a testament to the power of observation and innovation in the pursuit of knowledge about our universe.