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August 25th: Henrietta Swan Leavitt


Date: August 25, 2011

Title: Henrietta Swan Leavitt

Podcaster: Steve Arnold

Description: This is a brief insight into the life of Henrietta Swan Leavitt a woman who seems to be forgotten in history but played a very important roll in measuring the universe.

Bio: My name is Steve Arnold I’m an amateur astronomer from the UK I’ve been interested in all aspects of astronomy for as long as I can remember. Whether it’s history or cutting edge as long as it’s astronomy I don’t mind.

Sponsor: This episode of “365 days of Astronomy” has been sponsored by thesecretlair.com The Secret Lair is an online magazine and podcast dedicated to world domination and the plight of the grown-up geek. From an undisclosed location near Cleveland Ohio, Overlord Chris Miller, Dr. John Cmar, Commandant David Moore, and Secretary of Artistic Propaganda Natalie Metzger are joined by a stellar cast of contributors to share with you the trials, travails, and trivia of being a modern day working stiff with a strong escapist streak. There are lots of places covering pop culture on the Internet.

We bring a midwestern Everyman look at the world around us. If you find yourself somewhere between the ages of 20 and 60, have to deal with the responsibilities of paying for a roof over your head, credit card bills, car payments, and possibly raising kids, but you still like to read, play games, and talk with other mature adults about your obsession with Star Wars, drop by The Secret Lair. We’ll leave the lights on… and the portcullis up.”


Hello and welcome to the 365 days of astronomy podcast for today. I am your host my name is Steve Arnold I’m an amateur astronomer from the UK.

Today I would like to give you a brief account of the life of Henrietta Swan Leavitt, and how she discovered the relationship between the variable period and the luminosity of Cepheid variables. Which has allowed astronomers to measure greater distances into the universe.

Henrietta Swan Leavitt was born on the 4th July 1868 in Lancaster Massachusetts. She graduated from college in 1892. But being an educated woman at the time didn’t mean an awful lot as women were expected to stay at home to look after the children. In the late 1880s The Harvard college Observatory had embarked on a huge project to catalogue the position, brightness, and colour of every star in the sky. This was a massive task and this is where she found work after her graduation she was around 25 at the time. Women were hired to look at large glass photographic plates of the sky and compute the data hence these women were called computers. As you can imagine this work needed very good concentration and immense patience.

They would examine the glass plates calculate, measure and then record their observations in a ledger book. These glass plates are very fragile, and there are around half a million of these plates still surviving today so there were lots of plates for her and the other computers to work through. She did this work for approximately seven years. Then she was spotted by Edward Pickering and assigned the full time job of looking for variable stars in the Magellanic clouds. This type of work was very tedious and needed a vast amount of patience and accurate measuring. She would get two plates taken of the same part of the sky one a negative with black stars and the other a positive with white stars. The positive being taken a few days later. After placing the negative plate on top of the positive plate and carefully lining up the stars she would examine each star in turn using a magnifying glass. Any variation in a stars brightness would show up as a small white halo around a black star. If she found one of these halos she would make notes of the stars position and fetch other plates taken weeks or months apart and look for a Pattern.

She was very good at her work as a letter to Edward Pickering from a Princeton astronomer read “What a variable star fiend Miss Leavitt is one can’t keep up with the roll of the new discoveries”. She would work for hours on end systematically working her way through thousands of these plates. By this time she had become completely deaf and it is said that Edward Pickering would bring visitors to the observatory to the place where she worked and they would stand and watch her work but she was unaware of this because of her deafness. She was once asked if her deafness caused her a problem at work she replied “no as it made it easier to concentrate as she was less likely to be disturbed by the noise from others.”

She did this work for around ten years and discovered 1777 variable stars in the Magellanic clouds. But where her genius shone through was she discovered 25 of these stars pulsed with a regular Pattern. She found that the brighter stars pulsed slowly and the fainter stars pulsed quickly. She thought all the stars within the Magellanic clouds must be roughly at the same distance so if she knew the pulse rate she could work out the brightness of the star. Then if she had accurate measurement of the brightness of the star as it appears in the sky. She could work out the distance to that star or any galaxy containing one of these stars. So a new standard candle had been found all that had to be done was to find an accurate distance to one of these stars using parallax and this would calibrate the whole system.

In 1912 Edward Pickering published this news in a paper at Harvard and giving full credit to the work of Henrietta Leavitt. Unfortunately she took ill soon after this paper had been released and it was left to others to calculate this distance. But she did carry on her work at a reduced level due to her illness. Henrietta Swan Leavitt passed away on the 12th of December 1921 from cancer of the stomach.

The following year when the International Astronomical Union held it’s general assembly, the commission of Stellar Photometry of which she had been a member recognized “her great service to astronomy” and “She was one of the pioneers in a difficult field of investigation in which she worked with conspicuous success, and it is deeply regretted that she was unable to finish this her last undertaking”. But thanks to her work astronomers can now measure distances out to10 million light years or more as compared with the few hundred light years using parallax.

There is some conjecture whether she was nominated for a Noble Prize or not. There is a record of a letter sent from a Swedish mathematician in 1925 unaware that she had died asking for more information about her work with the intention of nominating her for the Noble Prize for Physics. But one of the rules for receiving a Noble Prize is the recipient must by alive. So technically she wasn’t nominated but she came close. But she did get some recognition as there is a crater on the moon named after her. I would like to end with a supernatural tale. For years after her death a ghost story was widely circulated around Harvard Observatory that her ghost moved among the racks of photographic plates, and that the glow from a single oil lamp had been seen at her desk.

I wish you clear skies goodbye.

End of podcast:

365 Days of Astronomy
The 365 Days of Astronomy Podcast is produced by the Astrosphere New Media Association. Audio post-production by Preston Gibson. Bandwidth donated by libsyn.com and wizzard media. Web design by Clockwork Active Media Systems. You may reproduce and distribute this audio for non-commercial purposes. Please consider supporting the podcast with a few dollars (or Euros!). Visit us on the web at 365DaysOfAstronomy.org or email us at info@365DaysOfAstronomy.org. Until tomorrow…goodbye.

One Response to “August 25th: Henrietta Swan Leavitt”

  1. Cassandra JB Polemi says:

    Thank you Steve Arnold, for writing such a nice document an making a podcast about my Great Aunt, Henrietta Swan Leavitt, whom i ever met, but have been inspired by all my life.
    I especially enjoyed the bit at the end about her ghost moving around the plates at Havard while an oil lamp burned at her desk. I have often thought she might have watched over my life, but would not be surprized if she wanted to continue her reserch after passin away. :-)

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