8 ms·

Chinese city to launch man-made moon to light up skies

40 points by dankohn1 8y ago

edejong 8y ago
I am sure the astronomy community will be thrilled... Infinite light pollution.
- nevi-me 8y ago
  I was thinking the same thing. I don't know how much light they will emit, but as someone who grew up in a village with very little light pollution; even something like a "satellite light" results in some pollution. I used to be able to see many constellations with the naked eye, until they put up 3 lights that are about 20m tall. My astronomy interest has waned as I can't see much with the lights. Now cue the "moons"
tummybug 8y ago
Sounds good in theory but would be interesting to know how prevalent cloud cover is in the city.
- everdev 8y ago
  Or smog
z2 8y ago
Here's a closer-to-ground design from over a century ago: https://en.wikipedia.org/wiki/Moonlight_tower https://en.wikipedia.org/wiki/Moonlight_tower
- sp332 8y ago
  And a reflective one: https://www.theatlantic.com/photo/2013/10/using-giant-mirrors-to-light-up-dark-valleys/100613/ https://www.theatlantic.com/photo/2013/10/using-giant-mirror...
LiterallyDoge 8y ago
Anyone seen Goldeneye recently? Great movie.
everdev 8y ago
Every satellite I've seen crosses the sky in seconds. How does an orbiting mirror provide consistent illumination? Can it orbit as show as the rotation of the Earth and still maintain an orbit?
- bspammer 8y ago
  See below
  - georgecmu 8y ago
    GPS satellites are not in geosynchronous orbits. In fact, they would be close to useless if they were (all in one line orbiting over equator). https://space.stackexchange.com/questions/10837/why-are-the-gps-constellation-satellites-in-such-a-high-orbit https://space.stackexchange.com/questions/10837/why-are-the-...
    - M_Bakhtiari 8y ago
      Why would a geosynchronous satellite have to be in one line over the equator? Why not a higher inclination?
      - rtkwe 8y ago
        If the orbit is inclined the satellite will no longer stay above a single point it will move north and south throughout the day. All orbits pass over the equator twice during each period.
        M_Bakhtiari 8y ago
        That's true, but it doesn't answer my question. Geosynchronous satellites can and do modify their inclinations and eccentricities to increase their coverage beyond one spot over the equator.
      - QuotedForTruth 8y ago
        They can have inclination other than 0. If inclination is 0 thats a "geostationary" orbit, a special case of geosynchronous. In fact these are not stable and degrade into mere geosynchronous orbits without station keeping. In general though geostationary orbits are more useful since they are fixed competely in the sky. Ground antenna dont have to track the satellite as it moves north/south in the sky.
jfk13 8y ago
I wonder what the impact will be on wildlife that depends on the hours of darkness?
- k33n 8y ago
  China isn't concerned with such things.
- rtkwe 8y ago
  If it works as intended it should be mostly focused over the city so the effects will be a lot lower than if they were illuminating a random patch of forest. I doubt they're particularly concerned with the environmental impacts though.
vertline3 8y ago
I wonder if there's more than meets the eye behind this?
- SketchySeaBeast 8y ago
  "That's no moon...."
KnightOfWords 8y ago
Colour me moonglow sceptical blue. At an altitude of 500km these 'moons' would cross the sky in a few minutes. Geosynchronous orbit is about 35,000km, but at that distance any artificial satellite would need to be vast to cast any significant light. Regular satellites at that distance aren't naked-eye visible. This report is, at best, seriously garbled.
- rtkwe 8y ago
  They can be visible its just relatively rare and only happens at certain times of the year depending on altitude when the solar panels line up. Flares like these are pretty much just a tiny accidental version of this already, something intentionally designed and controlled to produce them would in theory be pretty easy. My main thought is how well will this deal with the thrust that large of a mirror will be producing. It will essentially be a solar sail. Maybe they plan to rotate it during the day to provide the thrust to put it back into position? https://www.cloudynights.com/topic/530024-geostationary-satellite-flare/ https://www.cloudynights.com/topic/530024-geostationary-sate...
  - KnightOfWords 8y ago
    Interesting thanks, I didn't realise they ever got that bright. I've also captured geosynchronous satellites when imaging the Orion Nebula, they show up as parallel tracks. There is a big difference between producing a visible flare and actually providing illumination at that distance, that would require a huge surface. My best guess is that the original press release was talking about a paper project rather than anything there are any real plans to do.
    - rtkwe 8y ago
      There a large difference is but those flares are all produced by relatively small surfaces that aren't designed to reflect significant amounts of light (quite the opposite in fact) and a purpose built device.
- M_Bakhtiari 8y ago
chasing 8y ago
Cf. Austin, Texas.
T-A 8y ago
Relevant math here: http://jxcrystals.com/publications/Mirrors_in_Dawn_Dusk_Orbit_AIAA_Tech_Conf_Final_2013.pdf http://jxcrystals.com/publications/Mirrors_in_Dawn_Dusk_Orbi... Money quote: "Applying this formula for a mirror in orbit at an altitude of 4200 km gives a sun spot diameter on earth of 42 km". The report claims "The satellite would be able to light an area with a diameter of 10 to 80 kilometers, while the precise illumination range can be controlled within a few dozen meters", so either it's in a lower sun-synchronous orbit [1] (and maybe there is more than one) or it's a parabolic reflector [2] with controllable focal length, and there is no cause for concern. [3] [1] https://en.wikipedia.org/wiki/Sun-synchronous_orbit https://en.wikipedia.org/wiki/Sun-synchronous_orbit [2] https://en.wikipedia.org/wiki/Parabolic_reflector https://en.wikipedia.org/wiki/Parabolic_reflector [3] https://en.wikipedia.org/wiki/Sun_gun https://en.wikipedia.org/wiki/Sun_gun
- larkeith 8y ago
  Depending on the distance from Earth, it seems it could also act as a statite [1], which might allow for additional options in terms of illumination timeframes. [1] https://en.m.wikipedia.org/wiki/Statite https://en.m.wikipedia.org/wiki/Statite
- bassman9000 8y ago
  And they're assuming $0.1 per kWh, which is ok for the US, but could mean faster ROI around the world. https://www.ovoenergy.com/guides/energy-guides/average-electricity-prices-kwh.html https://www.ovoenergy.com/guides/energy-guides/average-elect... https://www.npr.org/sections/money/2011/10/27/141766341/the-price-of-electricity-in-your-state https://www.npr.org/sections/money/2011/10/27/141766341/the-...
emptybits 8y ago
Interestingly, until now, "light pollution" meant artificial sources. (i.e. with different colour and spectrum signatures such as CFLs, LEDs, etc.) Florida Atlantic University studies the impact of light pollution on plants[1] and animals[2] but I suspect many studies only partially apply to something like what Chengdu is doing because significant solar (or lunar) light pollution hasn't been available to study. Just a few concerns off the top of my head that I hope Chengdu will consider or at least study if it moves forward with this: circadian patterns, melatonin production, restful sleep, feeding patterns of nighttime predators (even in cities) including exhaustion of food sources (e.g. insects) that would naturally be difficult to find. Well this will probably improve human and traffic safety, but seriously hurt astronomy and dark sky appreciation for those who live there. And it's a given that all-seeing surveillance footage resolution will be improved! [1] http://cescos.fau.edu/observatory/lightpol-Plants.html http://cescos.fau.edu/observatory/lightpol-Plants.html [2] http://cescos.fau.edu/observatory/lightpol-environ.html http://cescos.fau.edu/observatory/lightpol-environ.html
justfor1comment 8y ago
Vegeta did it first.

40 points by dankohn1 8y ago

edejong 8y ago

I am sure the astronomy community will be thrilled... Infinite light pollution.

nevi-me 8y ago
I was thinking the same thing. I don't know how much light they will emit, but as someone who grew up in a village with very little light pollution; even something like a "satellite light" results in some pollution. I used to be able to see many constellations with the naked eye, until they put up 3 lights that are about 20m tall. My astronomy interest has waned as I can't see much with the lights. Now cue the "moons"

tummybug 8y ago

Sounds good in theory but would be interesting to know how prevalent cloud cover is in the city.

everdev 8y ago
Or smog

z2 8y ago

Here's a closer-to-ground design from over a century ago: https://en.wikipedia.org/wiki/Moonlight_tower https://en.wikipedia.org/wiki/Moonlight_tower

sp332 8y ago
And a reflective one: https://www.theatlantic.com/photo/2013/10/using-giant-mirrors-to-light-up-dark-valleys/100613/ https://www.theatlantic.com/photo/2013/10/using-giant-mirror...

LiterallyDoge 8y ago

Anyone seen Goldeneye recently? Great movie.

everdev 8y ago

Every satellite I've seen crosses the sky in seconds. How does an orbiting mirror provide consistent illumination? Can it orbit as show as the rotation of the Earth and still maintain an orbit?

bspammer 8y ago
See below
- georgecmu 8y ago
  GPS satellites are not in geosynchronous orbits. In fact, they would be close to useless if they were (all in one line orbiting over equator). https://space.stackexchange.com/questions/10837/why-are-the-gps-constellation-satellites-in-such-a-high-orbit https://space.stackexchange.com/questions/10837/why-are-the-...
  - M_Bakhtiari 8y ago
    Why would a geosynchronous satellite have to be in one line over the equator? Why not a higher inclination?
    - rtkwe 8y ago
      If the orbit is inclined the satellite will no longer stay above a single point it will move north and south throughout the day. All orbits pass over the equator twice during each period.
      - M_Bakhtiari 8y ago
        That's true, but it doesn't answer my question. Geosynchronous satellites can and do modify their inclinations and eccentricities to increase their coverage beyond one spot over the equator.
    - QuotedForTruth 8y ago
      They can have inclination other than 0. If inclination is 0 thats a "geostationary" orbit, a special case of geosynchronous. In fact these are not stable and degrade into mere geosynchronous orbits without station keeping. In general though geostationary orbits are more useful since they are fixed competely in the sky. Ground antenna dont have to track the satellite as it moves north/south in the sky.

jfk13 8y ago

I wonder what the impact will be on wildlife that depends on the hours of darkness?

k33n 8y ago
China isn't concerned with such things.
rtkwe 8y ago
If it works as intended it should be mostly focused over the city so the effects will be a lot lower than if they were illuminating a random patch of forest. I doubt they're particularly concerned with the environmental impacts though.

vertline3 8y ago

I wonder if there's more than meets the eye behind this?

SketchySeaBeast 8y ago
"That's no moon...."

KnightOfWords 8y ago

Colour me moonglow sceptical blue. At an altitude of 500km these 'moons' would cross the sky in a few minutes. Geosynchronous orbit is about 35,000km, but at that distance any artificial satellite would need to be vast to cast any significant light. Regular satellites at that distance aren't naked-eye visible. This report is, at best, seriously garbled.

rtkwe 8y ago
They can be visible its just relatively rare and only happens at certain times of the year depending on altitude when the solar panels line up. Flares like these are pretty much just a tiny accidental version of this already, something intentionally designed and controlled to produce them would in theory be pretty easy. My main thought is how well will this deal with the thrust that large of a mirror will be producing. It will essentially be a solar sail. Maybe they plan to rotate it during the day to provide the thrust to put it back into position? https://www.cloudynights.com/topic/530024-geostationary-satellite-flare/ https://www.cloudynights.com/topic/530024-geostationary-sate...
- KnightOfWords 8y ago
  Interesting thanks, I didn't realise they ever got that bright. I've also captured geosynchronous satellites when imaging the Orion Nebula, they show up as parallel tracks. There is a big difference between producing a visible flare and actually providing illumination at that distance, that would require a huge surface. My best guess is that the original press release was talking about a paper project rather than anything there are any real plans to do.
  - rtkwe 8y ago
    There a large difference is but those flares are all produced by relatively small surfaces that aren't designed to reflect significant amounts of light (quite the opposite in fact) and a purpose built device.
M_Bakhtiari 8y ago

chasing 8y ago

Cf. Austin, Texas.

T-A 8y ago

Relevant math here: http://jxcrystals.com/publications/Mirrors_in_Dawn_Dusk_Orbit_AIAA_Tech_Conf_Final_2013.pdf http://jxcrystals.com/publications/Mirrors_in_Dawn_Dusk_Orbi... Money quote: "Applying this formula for a mirror in orbit at an altitude of 4200 km gives a sun spot diameter on earth of 42 km". The report claims "The satellite would be able to light an area with a diameter of 10 to 80 kilometers, while the precise illumination range can be controlled within a few dozen meters", so either it's in a lower sun-synchronous orbit [1] (and maybe there is more than one) or it's a parabolic reflector [2] with controllable focal length, and there is no cause for concern. [3] [1] https://en.wikipedia.org/wiki/Sun-synchronous_orbit https://en.wikipedia.org/wiki/Sun-synchronous_orbit [2] https://en.wikipedia.org/wiki/Parabolic_reflector https://en.wikipedia.org/wiki/Parabolic_reflector [3] https://en.wikipedia.org/wiki/Sun_gun https://en.wikipedia.org/wiki/Sun_gun

larkeith 8y ago
Depending on the distance from Earth, it seems it could also act as a statite [1], which might allow for additional options in terms of illumination timeframes. [1] https://en.m.wikipedia.org/wiki/Statite https://en.m.wikipedia.org/wiki/Statite
bassman9000 8y ago
And they're assuming $0.1 per kWh, which is ok for the US, but could mean faster ROI around the world. https://www.ovoenergy.com/guides/energy-guides/average-electricity-prices-kwh.html https://www.ovoenergy.com/guides/energy-guides/average-elect... https://www.npr.org/sections/money/2011/10/27/141766341/the-price-of-electricity-in-your-state https://www.npr.org/sections/money/2011/10/27/141766341/the-...

emptybits 8y ago

Interestingly, until now, "light pollution" meant artificial sources. (i.e. with different colour and spectrum signatures such as CFLs, LEDs, etc.) Florida Atlantic University studies the impact of light pollution on plants[1] and animals[2] but I suspect many studies only partially apply to something like what Chengdu is doing because significant solar (or lunar) light pollution hasn't been available to study. Just a few concerns off the top of my head that I hope Chengdu will consider or at least study if it moves forward with this: circadian patterns, melatonin production, restful sleep, feeding patterns of nighttime predators (even in cities) including exhaustion of food sources (e.g. insects) that would naturally be difficult to find. Well this will probably improve human and traffic safety, but seriously hurt astronomy and dark sky appreciation for those who live there. And it's a given that all-seeing surveillance footage resolution will be improved! [1] http://cescos.fau.edu/observatory/lightpol-Plants.html http://cescos.fau.edu/observatory/lightpol-Plants.html [2] http://cescos.fau.edu/observatory/lightpol-environ.html http://cescos.fau.edu/observatory/lightpol-environ.html

justfor1comment 8y ago

Vegeta did it first.