Exploring nine simultaneously occurring transients on April 12th 1950 (2021)
nature.com
nature.com
Nine point sources appeared within half an hour on a region within ∼ 10 arcmin of a red-sensitive photographic plate taken in April 1950 as part of the historic Palomar Sky Survey.
It is interesting because the folks who made these photos in the 50’s were themselves scientists and existed in a society different from but of course pretty close to our own. I wonder if they thought of these photos as a record for posterity, or just an incidental work-product (I guess at least a little bit of the former, because some effort has been put into preserving them). I wonder what they imagined we’d do with them. I wonder what they’ll do with our ancillary work-product in 70 years.
It is pretty funny that we’ve got this giant worldwide network, and it is probably easier for us to combine observations from their datasets than it even was for them. They’d have to at least walk down the hallway if they wanted to borrow a “good” copy photo from a colleague.
Typically both. That's why the plates were carefully cataloged. It was not uncommon for plates to be exposed/developed and not actually be looked at by a researcher for months or years.
It's not researchers were lazy but if they were doing a survey and have 100 plates it took time to get through them. A plate needs its provenance cataloged so when handed to a research assistant they've got the metadata needed to properly catalog the plate's contents. Even in the plate days researchers would do meta-surveys comparing plates they may have done with archived plates made years or decades prior.
Lots of comets, asteroids, and other transient phenomena have been discovered because a researcher has been able to look at decades worth of exposures to some patch of sky.
In the 90s I remember reading about a lot of universities/observatories digitizing their plates (then on CD-ROM) so they were more readily available to contemporary researchers.
Before / After
the sky is changing constantly, just on scales we don't have the patience to witness. it's not unlike those before/after hurricane/tornado/fire/flood satellite images.
there's also the parallax tests where you image the sky, and then image the same thing in 6 months so that the earth has moved ~halfway around its orbit. overlay the 2 images, and you can see slight shifts.
also, now, the AI is being used to find things mere mortals have missed. several comets have been found using older images stacked to see things moving in a timelapse fashion. they've been used to find supernovae and other things where there's something brighter in one image, but was not that bright in previous images, and not so bright in subsequent images.
No doubt. There's a term of art of recovering images of newly discovered comets from old photographic plates, Precovery https://en.wikipedia.org/wiki/Precovery
"The best way to exclude the possibility of contamination causing the simultaneous transients is by examining the original photographic plates with a microscope11. Unfortunately, we have no access to the original POSS-I plates."
Was a bit surprised that they have produced this detailed article describing all possible sources they could come up with, and got it published in Nature but didn't check the originals..
Until it is.