A riff on the NASA James Webb Space Telescope logo. Instead of "Webb" it says "Leavitt"

On 25 December 2021 the most advanced space telescope to date was launched. A joint mission between NASA, ESA, and CSA it’s meant to find new exoplanets and look back in time to take pictures of the earliest galaxies ever to form. Undoubtedly this will bring many new scientific discoveries. We propose that it should be named the Henrietta Swan Leavitt Space Telescope, or Leavitt Space Telescope for short.

Many space probes and telescopes are named after scientists who made foundational contributions in the relevant fields. There’s Cassini, named after Giovanni Domenico Cassini, who discovered four of Saturn’s moons and was the first to describe the Cassini Division in its rings. There’s Chandra, named after Subrahmanyan Chandrasekhar, who made many contributions to theoretical astrophysics. Among many other things he figured out the maximum total mass of a white dwarf, an important contribution to the understanding of supernovae. Most notably there’s Hubble, named after Edwin Hubble, who was the first to prove that the Milky Way is not the whole universe, but merely one galaxy among many, based on Henrietta Swan Leavitt’s work.

Starting in 1903 Leavitt was working at Harvard College Observatory, where she had previously obtained credits towards a degree she never finished. As a woman she wouldn’t have been allowed to operate a telescope anyway, so instead she was working as a computer. She spent years identifieing 1777 variable stars in the observatory’s collection of photographic plates, among them a number of Cepheids. Realizing that to a first approximation all stars in either Vutha Varkla (otherwise known as the Small and Large Magellanic Clouds) would be the same distance away, Leavitt figured out that there’s a direct relationship between a Cepheid’s period and its luminosity, known today as Leavitt’s Law.

In other words, if you record the changes in how bright a Cepheid appears over time, you can figure out how much light it actually emits. If you compare this to how much of the emitted light arrives at earth, i.e. how bright it appears, you can calculate how far away it is. Objects like this, that have a well-known absolute brightness and thereby allow distance measurements on astronomical scales, are known as standard candles, and Cepheids were the first. Standard candles are both rare and extremely important, because measuring distances to other stars or even galaxies is a very hard problem. There are no rulers in space.

Up until Leavitt’s discovery, the distance to other stars would be measured by using a method called stellar parralax, that even today barely works beyond 10,000 light-years or so. Andromeda (our closest neighbour after a number of galactic lightweights like the Vutha Varkla) is 2.5 Million light-years away, and the Milky Way itself is 100,000 to 200,000 light-years across (we don’t really know because you guessed it–hard to measure). So lacking an acurrate way to measure the distance we simply couldn’t tell if those weird blobs in the sky were some kind of cloud and a part of the Milky Way or something like the Milky Way, outside and really, really far away. This was the subject of the Great Debate, one of Astronomy’s trending hashtags in the early 20th century, which Hubble (the scientist) was able to settle using Leavitt’s Law after observing Cepheids in Andromeda.

Without Leavitt’s work, he wouldn’t have been able to make this groundbreaking discovery. One of her colleagues, Gösta Mittag-Leffler, tried to nominate her for the Nobel Prize in 1925, but it was too late–Leavitt died in relative obscurity in 1922 at the early age of 53, and the Nobel Prize isn’t awarded posthumously.

It’s not, however, too late to honor her by naming a telescope after her, and what better telescope to bear her name than Hubble (the telescope’s) successor? When it was named, women were often overlooked when it came to honors like this. They were often overlooked in science in general. Despite a lot of progress that has happened since this is still largely the case–there’s a single planned mission named after a woman, the Nancy Grace Roman Space Telescope. In other words, the number of past or current space probes named after a non-male scientist is zero. But we can do better, and it’s about time that Henrietta gets her telescope.

But What About James Webb?

The telescope in question is currently known as the James Webb Space Telescope, after a former NASA administrator. This is not about Webb as a person–we’re sure he made contributions of his own. This is about rectifieing the gross imbalance between the number of telescopes named after men (all of them, not counting the ones with acronyms for names) and those named after not-men (again, zero). It’s also about giving a great scientist the recognition she was denied until now.