3066: Cosmic Distance Calibration

Cosmic Distance Calibration

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Title text: This is the biggest breakthrough since astronomers noticed that the little crosshairs around red giant stars starting to burn helium are all the same size.

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Explanation

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Transcript

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Discussion

yay. DollarStoreBa'al (talk) 16:31, 21 March 2025 (UTC)

What makes such labels as real objects absurd is not the required size, but the required orientation to be readable from a single point in the universe - earth. 172.71.154.9 19:26, 21 March 2025 (UTC)

All facing towards us AND all the right way up! That's geographically unlikely.  ;-) Robert Carnegie [email protected] 172.71.178.157 10:11, 22 March 2025 (UTC)

A straightforward application of the Anthropic principle. 104.23.187.189 19:35, 21 March 2025 (UTC)

I'm not sure I get the title text... 162.158.62.162 20:04, 21 March 2025 (UTC)

I like this part of the linked article: But cosmologists get only one universe to observe. -- Hkmaly (talk) 20:09, 21 March 2025 (UTC)

I think that the crosshairs in question are markers to indicate which star is being labeled, not anything to do with video games. 162.158.137.59 23:46, 21 March 2025 (UTC)

That's my suspicion as well: just markers like the labels, not diffraction spikes or anything like that. BunsenH (talk) 03:41, 22 March 2025 (UTC)

The crosshairs are all the same size because new red giant stars are all the same brightness. They are "TRGB" or "Tip of the Red Giant Branch" standard candles. Every star in that phase of evolution is exactly the same absolute brightness, so we can tell how far away it is by measuring the observed luminosity. 162.158.212.132 00:35, 22 March 2025 (UTC)

2035: Dark Matter Candidates also hypothesizes that astronomical labels are physically there, the orbit paths in this case. Should it be added? Intara (talk) 00:43, 22 March 2025 (UTC)

OH MY GOD! Why are there two blue boxes saying we need to complete 58 explanations? I would suggest that just one would be less distracting/disruptive. 172.68.2.70 03:19, 22 March 2025 (UTC)

Perhaps one box wasn't enough... although it seems reasonable to have an increasing number of cartoons that nobody felt able to explain. Robert Carnegie [email protected] 172.70.91.29 10:15, 22 March 2025 (UTC)

I agree. I put the second box it in on request at an earlier time, when it said something different. But have now removed the top box. That there are 60+ incomplete explanations can still be seen from the one I left. --Kynde (talk) 08:39, 23 March 2025 (UTC)

Thanks. Unfortunately that second box didn't have the desired effect, it just resulted in some removals of incomplete notices without the issues being fixed. --FaviFake (talk) 09:15, 23 March 2025 (UTC)

Regarding the crosshairs: TBH, I don't think the comic refers to diffraction patterns/spikes. I think it simply refers to literal crosshairs, as in "some stars are marked with crosshairs in this image and the astronomers think those crosshairs are some kind of real, physical phenomena". See the comic itself for an example of such a crosshair (the zoomed star has one!). --172.68.7.138 05:39, 22 March 2025 (UTC)

After noticing that other comments in this discussion page mentioned the same as I did, I took the liberty to update the text. --172.68.12.34 05:48, 22 March 2025 (UTC)

This comic seems extra ironic, given that NASA has been grossly misreporting the distances to extremely distant objects lately, due to lack of adjustment for observed differences in spacetime, in order to express things "simply". Most people of course don't care & those using more reliable resources are unaffected, but hobbyists & reporters etc are going "Wait, what? Those numbers are way off..." ProphetZarquon (talk) 14:16, 22 March 2025 (UTC)

There's surely no problem with stars having labels that look like they are to be read only by us, at our distance (and at this time). All each star needs to do is to send out highly-directional flashes (relatively, at least!) of light, such that the ones that will arrive at Earth around now were projecting information suitable for us back then, but light arriving at stars five hundred years ago, at a similar distance on a perpendicular track, will feature suitable information shone out five hundred years earlier (while sending vaguely in this direction only information destined to be useful for the star 'between' us, five hundred light-years in that direction). I'm sure you can appreciate how simple it is to accomplish this, all you need to do is have different patterns of photos continually travelling out in different sectros of different shells of ever-changing light, out into the universe, all ready to convey exactly the right information to the observer who happens to eventually be where the light gets observed, inexactly the right orientation and notation/language, as well! Simple! 172.68.205.92 22:58, 23 March 2025 (UTC)

Holograms are a thing, people. A different label could be aimed at each viewer. Heck, there might only be one viewer at present. And who said the labels are made of matter? This is the worst explanation page I have ever seen here. 172.68.54.235 11:43, 24 March 2025 (UTC)

Though holograms don't just appear 'in thin air' (or, indeed, vacuum). You're either looking at a medium imprinted with a clever diffraction patterns to shape the intensity of light projected out in various directions, or illuminating an amorphous media with precisely targeted light (e.g. lasers in a very mildly misty atmosphere, so that only where you have the brightest lines of laser, or the convergence of two or more less obvious beams, do you get omnidirectionally visible lines/areas/voxels) to produce an apparent object.

If you could always just magic up photons out of nowhere, you could have them appear (with the qualities required of them as if they had come from a star-adjacent emiter) in the last few light-years, or indeed light-seconds, in the middle of space heading exactly in the right direction (in exactly the right configuration) to be seen by your telescope. But that's getting towards God-tier 'causality'-bending. 172.69.43.241 11:59, 24 March 2025 (UTC)

2D & stereoscopic images can be projected directly at the viewer; a medium is only required if you don't know exactly where the viewer's receptors are... How would 'they' know? I dunno, why would they use English? I merely wanted to point out that projections can project directly to a receiver without a medium (with much lower requisite intensities). ProphetZarquon (talk) 13:16, 24 March 2025 (UTC)

Reverse the "seeing" principle (back to how people thought it was before Ibn al-Haytham overturned the "eyes shine 'vision' onto the world" idea). For every bit of hologram that you can see in front of you, project the vision backwards out of the eyes to where the hologram 'is'. At some point on that path, the must be something that is a source of the actual photons. It need not be where your stereo vision thinks it is. It can be much closer or much further, the holographic principle sending light as if from the non-physical surface of the holograph's mid-air location, probably then the images that your two eyes (and any further eyes/cameras) seperately see are from different bits of foreground/background that only carefully-tuned parallel makes you think is the mid-air point (like a Viewmaster stereoscopic viewer conveys false depth, or a Magic Eye picture lets you trick your eyes into associating neighbouring 'noisy' bits of image as being the same bit of noise either above or below the surface they're actually printed on).

To have a true mid-air source of light, the photons must be come from that location, and bright light (or multiple coherent bright lights, technically, in full holograms that aren't just a kind of Pepper's Ghost) must be scattered towards you from that location somehow, if it isn't already coming towards you from exactly (consistent with both detail and viewpoint/eye) the opposite/near side of the 'projection'.

If it's a hologram in a vacuum, for the sake of argument even having insufficient interstellar dust to 'project' upon and reflect every which way, then you can shine your holographic projection however you want at that empty space, but you won't see anything of it. You need to combine with back-projection, front-projection or possible side-projection onto a 'screen' of suspended material that is insignificantly visible where you don't shine the light properly, and that's messy enough to have observers at all kinds of angles getting angled views of the same thing (which is where you need to tune the interference patterns to be only constructive in the right ways, the whole trigk behind a true holographic 'display', either print/transarency medium or whatever the properly coherent light is sent to land on from the holographic source).

With clever retro-reflective particals, you could project from somewhere roughly between you and the 'hologram', that you are looking past, or even effectively itself shining past over your shoulder, and limit the intended view to a viewer only in your sort of direction, but that takes a different kind lf trick to set up, and wouldn't easily allow true stereoscopy, just pretend perspective-based tricks. 172.69.34.175 17:45, 24 March 2025 (UTC)

Is it just me or does that look like the label and crosshair in Space Engine? 172.71.147.60 23:48, 24 March 2025 (UTC)
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