I have to stop taking stuff for granted. At a recent star party, I was asked how it was first determined that what looked like one of the many nebulae within the Milky Way Galaxy was actually something much, much farther away. How did it come to be known as the Andromeda Galaxy? I gave a mumbling answer that satisfied neither myself nor the questioner. In my laziness, I’ve simply always accepted that someone, somehow, just plain figured it out.
Annoyed with myself, that night I went home and looked it up online. Here’s what I found out.
Well over 100 years ago, a group of women—the Harvard Computers—were hired by Edward Pickering, the director of the Harvard College Observatory, to organize and analyze the countless photographs he and his colleagues took of the night sky. One of the women, Henrietta Leavitt, came upon a remarkable discovery in 1912 while studying the characteristics of some very unique stars called Cepheids.
Their name derives from a star in the constellation Cepheus, that was observed to pulsate in a very predictable manner. That star, it was learned—and all others like it—undergoes a period of expansion and contraction of their surface that manifests not just in a change in diameter and temperature but, most significantly, in a marked change in luminosity.
Leavitt realized that there was a direct correlation between the brightness, or magnitude, of Cepheids, their periods of stability and change, and their distance from Earth. The equation she developed—the Period-Luminosity Relation—was used some years later by Edwin Hubble to prove that ours was not the only galaxy.
It was Hubble who calculated that Andromeda was too far out in space to be part of the Milky Way. That quickly led astronomers to understand that the universe was even more immense than anyone had yet imagined.
Relying on Leavitt’s work, Hubble was able to show that the universe itself was increasing in size. Jump forward about another 100 years and astronomers, now standing on both Leavitt’s and Hubble’s shoulders, proved that the rate of expansion of the universe was actually accelerating over time.
It all began with Henrietta Leavitt, a graduate of Harvard’s School for Women (now Radcliffe) who took her first astronomy class as a college senior.
With jobs for women hard to come by, she volunteered at the Harvard Observatory. Only later was she paid for her highly detailed work, earning a whopping $0.35/hour. She stayed at the observatory for 30 years, passing away at the age of 53 in 1921.
Sadly, Leavitt died before she and everyone else realized just how important her discovery and equation were to the field of astronomy. Today, she is revered.
As for Leavitt’s Cepheid stars, there are quite a few. Perhaps, the most well-known is Polaris, the North Star. Like all Cepheids, it is massive and very bright, approximately 2,500 times brighter than the Sun. It marks the end of the handle of Little Dipper and always points the way north because it is positioned over the North Pole. Located about 450 light years away, Polaris is part of a triple star system, one of three stars forever bound together. Unfortunately, even though it grows more luminous over its four-day period, the change is still too slight to be seen with the naked eye.
I’ve never given Polaris much thought, other than using it to confirm the direction I was facing. I never knew it was a triple and certainly never knew it was a Cepheid. I also never knew anything about Henrietta Leavitt, or the other women at the Harvard Observatory who did all of the behind-the-scenes work for the all-male astronomy staff.
It’s so easy to take so much for granted, to reap the benefits of someone else’s genius, persistence and devotion without ever pondering how an invention or a mathematical formula or even a perfect loaf of Italian bread come to be.
So, to whomever it was that asked me that question about Andromeda—thanks for the push. Thanks for reminding me to be mindful of the people and the histories behind the miracles that become all too commonplace over time. After all, I learned that Henrietta Leavitt is as awe-inspiring as her discovery.
Harold Meckler can be contacted at byaakov54@gmail.com