Henrietta Swan Leavitt and the SMC

24 Sep 2016

I can’t observe the Small Magellanic Cloud without thinking of Henrietta Swan Leavitt – ‘the woman who discovered how to measure the Universe’, as George Johnson, author of the book Miss Leavitt’s Stars, put it.

After all, it was from stars in the Small Magellanic Cloud that Leavitt discovered the period-luminosity relation of Cepheid variables that gave astronomers an incredible new measuring tool with which they could work out the distance to any Cepheid variable. The repercussions of this breakthrough were enormous. It gave astronomers the measuring tool whereby they could unravel the most basic question facing astronomers in the early twentieth century: Was the Milky Way essentially the entire universe, or was the Milky Way just one of many galaxies?

She made her discovery from photographs of the Small Magellanic Clouds that she was working on under the directorship of Edward Pickering, and under whose name her paper was published in 1912. Large glass photographic plates of the southern sky, taken with Harvard’s 24-inch Bruce Telescope in Peru, were sent back to Harvard for analysis. Her job was take each plate of the Small Magellanic Cloud, mount it on a device which illuminated it from behind, and using a magnifying eyepiece, carefully measure the thousands upon thousands of black dots representing each star on the negative image. She performed this painstaking task on repeated photographs over years.

Her job was to catalogue stars, not to investigate them. She made her momentous discovery on her own initiative.

Very little is known about the woman who made one of the most important discoveries in astronomy. She didn’t leave diaries or memoirs, and there are few letters. During her lifetime she received neither plaudits, nor acclaim, nor even recognition for her work, appearing only in footnotes and cursory references.

Despite her landmark discovery, she still receives an almost complete lack of recognition. No astronomy prize is named after her. No space telescope bears her name. No postage stamp has ever been issued to honour her. And unbelievably, there isn’t even a plaque to commemorate her name at the Harvard College Observatory where she worked, and where her far-reaching breakthrough in 1912 took place.  

All that marks her name is the asteroid 5383 Leavitt, the minor crater Leavitt on the far side of the Moon, and some virtual space on the Internet.

And to me… the entire lustrous Small Magellanic Cloud – and the most gorgeous little cluster within it…