Remembering Henrietta Swan Leavitt

The woman who gave us a Universal ruler

Henrietta Swan Leavitt

While talking about the History of Astronomy or other sciences, we hear very few names of women in the field. In the early 1900s era, it was very difficult for women to work outside their houses. But the astronomer Henrietta Swan Leavitt not only followed her passion for stars but also discovered a whole new way of measuring large distances to them.

Henrietta Swan Leavitt was born on this day, on 4th July in 1868. She worked in Harvard College Observatory, without pay! Later on, she was hired as a “human computer” in the same institute. She was one of the other few women working there as human computers. They have to do all the tedious work of calculations, only assisted by pencils and papers. Despite all the hurdles, Leavitt continued to work for her passion.

The work of observing brightness of variable stars was allotted to Henrietta Swan Leavitt. Due to the limitations of instruments, it was difficult to identify such stars. But Leavitt developed a new yet simple technique to identify and study them. She overlapped positive and negative photographic plates that showed the exact same spot in space days or weeks apart. Stars that had changed in brightness over that time, which were variable stars, appeared on the plate while the rest faded away. Thus Henrietta Swan Leavitt discovered 2,400 variable stars which comprised more than half of the total known variable stars even by 1930.

At that time, scientists did not know how to measure large distances to stars, (more than 1 kpc) with precision. Henrietta Swan Leavitt put forth a law based on her study of variable stars. This law could predict their exact distances. Leavitt studied the data of 25 variable stars and plotted a period v/s luminosity graph in which she found a logarithmic pattern.

She found that, “The brighter the star, the longer its period.”

Leavitt used this conclusion for other stars whose luminosities were unknown and observed their periods. Thus she could find their luminosities and furthermore, their distances from Earth!

Leavitt’s outstanding discovery helped many scientists like Edwin Hubble, Edward Charles Pickering in their research.
On the birth anniversary of legendary astronomer Henrietta Swan Leavitt, let us take a moment and appreciate her dedication to astronomy.

By Vallari Kurdukar

Ref: Biography on