Curved focal plane & photographic plates: why the hardware matters

1:17:542,000. Um, this is an example of one of the photographic plates. Um, it's a onederee by one degree patch of the plate that is targeting Pletes, the seven sisters. Um, and the the haziness that you see, that's actually not a defect. Those are actual clouds around those stars, those dust clouds around those stars that that are creating that. It's a beautiful beautiful example of one of the photographic plates that was actually taken during that time. The typical exposure was about 45 to 50 minutes. Um what we're focusing on here are the red sensitive plates. They used to take red sensitive and blue sensitive. Here we're focusing on the

1:18:34red sensitive because that's what was used in the study here. Um, and the limiting magnitude um is 22 in terms of apparent brightness. The higher the magnitude, the the dimmer the thingy is. And this is about 1 million times fainter than what the human eye can see. Okay. So that's what's limiting the faintest object that this telescope can see. >> Can see. That's like the the lower bound. >> Yes, that is the lower bound. So that's the telescope that we're using and that's how we're getting these images. Now, the photographic plates. We got to talk about the photograph. >> We got to talk about the plates. >> What does that mean? >> Yes. >> So, photographic plates are 14x4 in. And

1:19:14these 14x4 in are placed at the back of the camera where all of the light is coming in. It's 1 mm thick. These are incredibly thin for how big they are. They're like the size of a record, you know, a vinyl record. Um they've got a light they they've got a photographic emulsion on them. Okay. A light sensitive silver halli crystal layer. Usually it's silver broomemide and that's that's suspended in gelatin. Okay. Bromium is the h hallogen that they're using here. Halogen is like that column on the periodic table that's second to last on the right. These plates are bent as I was saying so that they can match the the the focal plane

1:19:56which I thought was just really cool to think about. Um and then the process is a photon comes in >> from your telescope and it liberates an electron in this silver broomemide and that electron that that liberation of the electron forms a latent image spec. You've got this free silver atom. Okay, that creates a silver atom cluster. Then during development that latent image spec catalyzes and the silver broomemide that's that's that's around there goes and turns into black metallic silver. Okay. And then finally you have a washer a kind of fixer that removes any unexposed silver broomemide. This is

1:20:37like the old school you know where you like wash the thingy and then that removes any >> silver broomemide and what you're left with is a permanent negative image. And that's why in the in the previous image that you saw, if you actually go back to photo two, you'll see in the previous image, the dark spots are actually where the light is. >> Okay? >> Right? >> Cuz that's where the silver is getting deposited. Okay? So you get this negative image, >> right? >> Of of the dark is actually where the light is coming in. >> Okay? And the white is where there was no photo reaction that happened. Okay? And so that's how we actually get these photographic plates. >> That's what a photographic plate

1:21:17>> that's what a photo photographic plate is. And that is what the chemical reaction of what a photographic plate means. Okay. Now what this what what what this sky survey is doing and and the the data that this particular group used is the digitized version of those photographic plates. Okay. So the digitized version in the 1980s and 1990s, we did a digitization process where those glass plates used um micro densitometers that basically went through and digitized these photographic plates. You've got a light beam that measures the opacity of the photographic

1:21:58plate and that converts that opacity into a digital pixel value. So the more opaque it is, that means that there was more dark, >> right? There was more darkness. And then if there's more darkness that means that the there's more light over there. And so and so now you've converted from >> photographic plates to a digital sort of pixel values, right? Yes. >> And there were two >> digitization processes that happened. Okay. There was the digital sky survey. Yes. >> That was um done with a pixel size of 25 microns. And then there was a

1:22:38supercosmos sky survey >> and that was done at the Royal Observatory of Edinburg >> with uh higher resolution of 0.7 arcseconds per pixel. >> Got it. Okay. So the first one was 1.7 arcsec per pixel and then this one's 0.7 arcsecond. So it's just like more gra like grainier detail, you know, sort of think about >> a slightly higher fidelity. Yes, exactly. And now you've got a vetting step, right? Where now we can create computer algorithms that look at these digital photographic

1:23:18versions and then try to find transients, little spots in the sky that aren't there in both aren't there in current photographs of that patch of the sky, >> but that were there >> that were there back then. Okay. >> Right. And what we can also do is we can rule out any scanning artifacts because we've got two different digital versions >> of the photographic plate. So if something happened in the scanning where I got a little speck that shouldn't be there in both at the same spot, >> right? The probability of that is insane. >> Is insanely high. The the point is the the the digital scans there's two there's two versions. >> And so if someone was at asleep at the

1:23:59wheel Yeah. when they scan version one, >> it should not be there in version two at the exact same spot >> in in such a precise >> exactly >> way. And so what what you're sort of there's a layer of of of validation. >> Yeah, there's like a redundancy here. >> Redundancy here because we have two digital >> Yeah, we have two digital versions of this. Okay. And so now we get into the Vasco project, right? Which is the vanishing and appearing sources during a century of observations. This is led by Beatatric Villa Roel. And the the point of this project is to have a systematic comparison between the

1:24:40digitized versions and modern sky surveys. Right? You look at what the Palomar Observatory saw back then and you look at what we're looking at right now. Yes. And you've got an automated software that flags these vanishing the present present then missing now, right? And there's also appearing. So not present then but appearing now, right? You've got an automated software that flags these things. And initially you've got a catalog of 100,000 transient candidates. And here we're seeing two different images. One from pass one, which is the first sky survey and pass two. And the circles represent two

1:25:21little spots that you can see are exactly not there in the second one. Right? It's like pretty obvious that those two dots were there before and now they're not there now. Right? And so that's a transient. You've got a point-like source that's there in some plates, but in the later plates it's not there. >> And the idea is, you know, we have two points in time and we should be seeing identical things in both those points in time. >> Yes. If it's a star then yeah >> because of >> and it's not identical. >> It's not identical. Right. So >> people are going to be skeptical about this. Right. For example, it could just be plate defects. Sure. Right. Both this

1:26:04this point of source of light or whatever this thing that we're seeing in the photographic plate, it's there in both the digital versions. Well, that means it could just be in the plate, right, itself. What is a hallmark of something that is in the plate? And this is something that comes from Nigel Hamley at the University of Edinburgh. He's one of the critics. He looks at something called the full width at half maximum of these points of light. Okay. So, the full width at half max is basically imagine you've got a gausian. Yeah. >> What you're what you're looking for is what is the width of that gausian when the height is half the the peak height. Okay. And what this tells you is

1:26:46something about the noise in the data gathering process. Now I told you this this um this telescope, right? It's traversing the night sky. >> Yes. >> And it's being controlled by a human being. Well, there's going to be a little bit of noise in how I control that telescope as it tracks, right? So, even a stationary point of light is going to have a little bit of jitter, right? As I move this telescope, the telescope is going to not totally track it completely. And even a point of light like a star that is definitely stationary over the 50 minutes at least, you know, it might be moving over like several years, but like over 50 minutes, it's stationary. that's going to have a

1:27:28little spread in my photographic plate. And what he noticed was these transients, the ones that the ones that sort of appear and disappear, they've got uh a spread that's way smaller >> than the stars. >> Mhm. >> Okay. >> Mhm. Yeah. Yeah. And that to him was a telltale sign that this is a defect because if it was a if it was a light source, then the light source should have the same sort of error that the stars do >> because they're all light, >> right? Does that make sense? >> It does. It does. >> Right. Like all of the other things have the same sort of spread because it's from the same jitter of the telescope. >> It's uniform across the system, >> right? >> Yeah. Yeah. Yeah. >> That's it's a it's a key thing. Yeah. >> Now, the contention is the the sort of

1:28:10counterargument is well, if it's truly transient, meaning like it only like lit up for a minute or a fraction of a second and it had a bright signature, then only one part of that 50-minute exposure is going to have that light come on and then it's going to go away. So then of course the full width at half max is going to be way shorter because >> it's not going to have time to accumulate that noise, right? But now we're here. We're at a degeneracy problem, right? Because a genuinely short-lived astronomical event, right? Something that happens for a fraction of a second is going to look identical to a

1:28:51plate artifact. >> Got it. Right. you know. Yeah. >> It's like you're looking for you're looking for a shortlived astronomical event, but that's going to look exact, you know. >> Yeah. Yeah. How do you distinguish between what is being argued as a plate artifact versus a true >> Yeah. >> uh short-lived transient event? Because it's hard to distinguish between those two. >> Yeah. Yeah. Yeah. The the the measure that we're using is degenerate to um discerning between one or the other. Does that make sense? >> It's it's it's one of the two. >> Yeah. But >> but like the measure that we have which is this full with a half max is like it's going to be the same for both. >> Got it.

1:29:32>> Right. So So which one is it? And that's why there was a necessity for an independent line of evidence. >> Okay. >> And this is where we're getting into the two papers that we have now. >> Okay. >> Okay. So it's it's this it's this challenge of well it could be a defect or it could be a truly transient object. Which one is it? And the the the interesting note here just as a a a caveat or a point of order is there there was a emphasis on this being you know the polymer sky survey which happened in the ' 50s was pre-sputnik yes uh sky survey and nowadays when we talk about transient

1:30:13light artifacts it's starlink it's other satellites, other whatever you Chinese classified platforms, but there's a lot of stuff >> Yeah. >> that we have now put up there. >> And so it is much easier nowadays to say, oh, it's X, Y, or Z. >> Yep. >> One of the interesting aspects of why this distinguishing between whether it's a plate artifact or not is if it's not, we're seeing these transient light anomalies at a time period where we

1:30:54>> we at least didn't put anything up there. Right. On purpose. >> On purpose. >> Right. It's this is from November 1949 to December 1958. This is before >> Sputnik, which could be interesting. >> Yes. >> Because of the fact that it can't just be pointed to being >> Starlink passed by. >> Exly. Exactly. Exactly. And so now that is where we're getting into the two papers that have come out from the Vasco project. Okay. What they've done is with the first paper, they're doing a spatial arrangement on individual plates and they're arguing about um the transients, how they look on individual plates, and where they are in the night sky in terms of

1:31:37when they were when these photographic plates were taken, where was the Earth's shadow, and if we can do some kind of statistical comparison and really show that these are stuff that's in the night sky and not photo photographic plate defects. And then there's a second paper that talks about temporal correlations in time between the stuff that we see in the photographic plates and stuff like nuclear tests and UAP sightings which we'll get to. So study one, this is the alignment hypothesis. This is Villa Royale um and others in 2025 in PASP. Yes, the paper

1:32:18is aligned multiple transient events in the first Palomar Sky Survey. The hypothesis is that these multiple pointlike transients are aligned along a straight line on the same plate, which is very unlikely by chance, and they could be real physical objects. And that is the argument that they're making. Okay. So, they've got a catalog of about 300,000 short duration transients from this Palomar survey that we just went into. >> Yes. >> Okay. And the first thing that they do is they ask how many of these things are aligned. They're in a line. Okay. And here we've got a photo um of plate five. This is

1:32:58candidate five. >> Mhm. >> There's five different thingies that are all in a line. Okay. And they use this thing the the a statistical framework from Edmunds and George published in 1985. and it calculates how often you would expect these things to happen by chance. >> Okay. >> Okay. And they find a sigma of 3.9 that this is not chance. >> Okay. >> Okay. 3.9 is it's pretty high. Okay. It's it's not like five sigma which we've talked about in our previous