I realize I’m stretching the Thinking Meat theme with this post, but the story touches on so many of my favorite things that I’ve just got to write about it. It demonstrates the wonderful things we hominids are capable of when we set our minds to it, and is also an interesting take on the difficulties of storing and accessing the riches of scientific data that our forebears have laid up for us.
Harvard College Observatory is a venerable institution that plays a large role in many of the exciting astronomy stories of the second half of the nineteenth century and on into the twentieth. From the first photograph of a star, taken at the observatory in 1850, through the 1980s, the HCO accumulated glass photographic plates from several observing sites in both hemispheres. This article from the New York Times describes efforts to digitize this huge trove of historical information about the night sky, our window into the universe. It’s a challenging endeavor any way you look at it, but letting all this painstakingly gathered information go to waste for lack of easy access would be a shame. (If you love observatories, check out the “More photos” link under the two photos at the top.)
The article mentions in passing a couple of the stories about how research at HCO played a pivotal role in creating contemporary astrophysics. For example, the tireless Annie Jump Cannon cataloged nearly 400,000 stars according to their spectral type. She examined the spectra of these stars as captured on glass photographic plates, hundreds of tiny smears of light to a plate, each with a characteristic pattern of dark lines that reveal a surprising amount of information about the star’s physical characteristics. She improved upon the classification schemes of two predecessors and tagged each star as belonging to a particular type (her scheme is the one still in use today). Her work was essential for later discoveries about why there are different types of stars and how stars evolve.
Another great story is that of Henrietta Swan Leavitt, who made a discovery about a particular kind of variable star that unlocked the distance scale of the cosmos. Cepheid variable stars periodically brighten and then dim in a regular cycle, and she found that the length of time between two episodes of maximum brightness is related to the intrinsic brightness of the star. This is important because without some such relationship to guide us, we can’t tell the intrinsically dim nearby stars from the intrinsically bright stars at a great distance: we don’t know cosmic distances. Ejnar Hertzsprung calibrated the yardstick that Leavitt had found, and Edwin Hubble used it to measure how far away the Andromeda Galaxy was, resolving one of the great astronomical debates of the early twentieth century: the spiral nebulae are not part of our galaxy but are separate “island universes” like our own.
The digitization project at Harvard (Dasch: Digital Access to a Sky Century at Harvard) also involves some heroic hominids who found a way to scan the plates, within the constraints of time and space imposed by the volume of data and the physical setup of the archive. The project is underway but needs more cash to continue, so the organizers are hoping for generous donors who might like the chance to associate their names with the resulting digital archive. The catalog that Cannon worked on is called the Henry Draper Catalog, and was funded by the widow of Henry Draper, a doctor, astronomer, and early astrophotographer. To this day stars are identified by their HD catalog numbers; I hope some rich Harvard alum is captured by the idea of leaving a similar legacy and donates money to keep the project going.
[Postscript, December 28, 2023: If you’re interested in the stellar classification work done at Harvard College Observatory, I highly recommend Dava Sobel’s wonderful book, The Glass Universe: How the Ladies of the Harvard Observatory Took the Measure of the Stars.]
