APOD: Cosmos in Reflection (2023 Sep 22)

[APOD Robot]

Cosmos in Reflection

Explanation: During the day, over 12,000 large mirrors reflect sunlight at the 100-megawatt, molten-salt, solar thermal power plant at the western edge of the Gobi desert near Dunhuang, Gansu Province, China. Individual mirror panels turn to track the sun like sunflowers. They conspire to act as a single super mirror reflecting the sunlight toward a fixed position, the power station's central tower. During the night the mirrors stand motionless though. They reflect the light of the countless distant stars, clusters and nebulae of the Milky Way and beyond. This sci-fi night skyscape was created with a camera fixed to a tripod near the edge of the giant mirror matrix on September 15. The camera's combined sequence of digital exposures captures concentric arcs of celestial star trails through the night with star trails in surreal mirrored reflection.

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[Rauf]

There's been a mistake I guess. Today's APOD incorrectly shows the date as September 21, and the link to Asterisk Discussion page also directs you to September 21.

[RJN]

There's been a mistake I guess. Today's APOD incorrectly shows the date as September 21, and the link to Asterisk Discussion page also directs you to September 21.

Thanks! Just fixed. We apologize for the inconvenience!

[johnnydeep]

I don't get why the reflected sky shows so much wavy distortion of the star trails. Are the mirrors of the array not almost perfectly flat? The "surreal mirrored reflection" video link does seem to show clear undistorted images of the sky, which would seem in indicate very flat mirrors.

[Chris Peterson]

I don't get why the reflected sky shows so much wavy distortion of the star trails. Are the mirrors of the array not almost perfectly flat? The "surreal mirrored reflection" video link does seem to show clear undistorted images of the sky, which would seem in indicate very flat mirrors.

Hmm. What I see in the video looks like a highly distorted view of the sky. There is no reason for the mirrors to be very flat. Between their intrinsic nature and whatever frame is holding them, I'd expect quite a bit of "waviness".

[johnnydeep]

I don't get why the reflected sky shows so much wavy distortion of the star trails. Are the mirrors of the array not almost perfectly flat? The "surreal mirrored reflection" video link does seem to show clear undistorted images of the sky, which would seem in indicate very flat mirrors.

Hmm. What I see in the video looks like a highly distorted view of the sky. There is no reason for the mirrors to be very flat. Between their intrinsic nature and whatever frame is holding them, I'd expect quite a bit of "waviness".

Well, I'll be damned, you're absolutely right! I didn't look closely enough and was fooled by the fact that the video shows time-lapsed motion whereas the image of the mirrors in the APOD uses a very long exposure that is ideal for recording wavy motion over time.

[johnnydeep]

One other dumb question: since the mirrors aren't being used to capture solar energy at night, I don't suppose there would be any practical and cost effective way to design a dual purpose configuration of specially made mirrors what would focus sunlight for power during the day, but then switch to focusing incident radiation onto a detector for astrophotography at night?

[Chris Peterson]

One other dumb question: since the mirrors aren't being used to capture solar energy at night, I don't suppose there would be any practical and cost effective way to design a dual purpose configuration of specially made mirrors what would focus sunlight for power during the day, but then switch to focusing incident radiation onto a detector for astrophotography at night?

Well, then you would need optically flat mirrors, which would be astronomically (ha, ha!) more expensive. There might be astronomical applications that are fundamentally about energy collection (as opposed to imaging), like the cosmic ray detectors that detect Cherenkov radiation flashes, that could ride piggyback on a system like this.

[johnnydeep]

One other dumb question: since the mirrors aren't being used to capture solar energy at night, I don't suppose there would be any practical and cost effective way to design a dual purpose configuration of specially made mirrors what would focus sunlight for power during the day, but then switch to focusing incident radiation onto a detector for astrophotography at night?

Well, then you would need optically flat mirrors, which would be astronomically (ha, ha!) more expensive. There might be astronomical applications that are fundamentally about energy collection (as opposed to imaging), like the cosmic ray detectors that detect Cherenkov radiation flashes, that could ride piggyback on a system like this.

That's interesting. How about making a huge radio telescope with each mirror merely supporting a segment of a metal grid that would focus radio waves onto a detector at night? The tolerances for a radio telescope are less stringent than for optical right? Or is that a misconception?

[Jim Leff]

Don’t miss the photographer’s two minute making -of video (linked in the APOD text) which gives great context plus a witty reference to the “Three Body Problem” sci-fi trilogy: https://www.youtube.com/watch?v=3Pbr2wIgCHE

[orin stepanek]

I was mesmerized by the mirrors!

[johnnydeep]

Don’t miss the photographer’s two minute making -of video (linked in the APOD text) which gives great context plus a witty reference to the “Three Body Problem” sci-fi trilogy: https://www.youtube.com/watch?v=3Pbr2wIgCHE

Yeah, I've really got to read that book. I was blown away by the description of an incredibly inventive idea in https://www.fictionunbound.com/blog/201 ... dy-problem, in which a proton is "unfolded" to become ridiculously huge lines, cubes or planes. Quite a mind-blowing concept for afficianodo's of higher dimensional math concepts (hyper cubes, etc.)

A late sequence in The Three-Body Problem—whose translation, by Ken Liu, is now out in paperback—depicts a massive project to unfold a single proton into two dimensions, etch microprocessor circuitry on to its surface, and turn it into a supercomputer. The idea is ambitious, fantastic geek porn. Subatomic particles, under superstring or M-theory, exist in as many as eleven space-time dimensions, of which we only perceive the standard three (plus time); and just as one can unfold a cube into a flat, larger cross, or a 4-D hypercube into a ‘larger’ three-dimensional shape, the scientists in Three-Body unfold the proton’s compact eleven-dimensional shape into lower-dimension shapes, each more expansive than the last—with the 2-D proton so large, it has to be manipulated in orbit because it wraps around the planet.

[Avalon]

This sounds like a perfectly benign energy source, but the price is often high as the beam of concentrated 900 degree solar energy kills birds that unfortunately fly through it. https://www.youtube.com/watch?v=emBY6phmn9E

[johnnydeep]

This sounds like a perfectly benign energy source, but the price is often high as the beam of concentrated 900 degree solar energy kills birds that unfortunately fly through it. https://www.youtube.com/watch?v=emBY6phmn9E

I presume the risk is greater the closer to the focal point you go because the temperature would get progressively hotter due to more overlapping beams from the mirrors. Seems like there could be mitigating solutions. Perhaps enclose the inner hottest volume with a wire mesh that would let most of the light through but keep birds out. Or construct the whole thing in a large depression and cover it all with such a mesh.