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midtskogen
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Light pollution

26 May 2019 23:48

I don't think we have a separate thread for light pollution.

Let me start with an issue which is perhaps not so often considered light pollution, but it should be, in particular these days when SpaceX has begun rolling out its broadband satellites.  Namely: satellites.  Perhaps a curiosity for many to spot one, but at high latitudes they're already very visible.  In Norway you can almost always spot a satellite in the sky if you look up in the dark.  In Svalbard several are usually visible at any time.  And some can briefly reach -9 magnitude.  It's getting really crowded up there.

Satellites become visible because they reflect sunlight, and satellite are intentionally built shiny to protect it from the sun's heat.  Could there be a solution to this problem, that nobody has tried simply because the right people haven't though about it?

Considering that we're able to create paint of any colour easily, it would be surprising if it isn't possible also to produce a finish for satellite that absorb visible light, but reflect infrared light.  That is, to "paint" satellites in pure infrared.
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Light pollution

27 May 2019 03:17

Paint can add up in overall weight surprisingly fast - especially if it is specially-treated to absorb light (since these additives would make the paint thicker and thus heavier). This won't make much difference on small satellites - but bigger ones would require more paint. Since most of these companies just go for the cheapest solutions possible, I can't see them spending extra money on painting all of their satellites a certain color and even more for the additional cost of sending a heavier satellite up. But you are absolutely right - as more infrastructure goes up into space, this problem will only get worse.
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Light pollution

27 May 2019 13:40

midtskogen wrote:
Source of the post Considering that we're able to create paint of any colour easily, it would be surprising if it isn't possible also to produce a finish for satellite that absorb visible light, but reflect infrared light.  That is, to "paint" satellites in pure infrared.

The Sun radiates most strongly in visible light, so absorbing that while reflecting IR wouldn't do any favors for thermal management. There's also the issue of solar panels and antennas, which are usually the strongest reflectors of light on most satellites, and which often cannot be painted without impairing their function.
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Light pollution

27 May 2019 23:42

midtskogen wrote:
Source of the post And some can briefly reach -9 magnitude.

This in particular is caused by specular reflection off of the solar panels or antennas (Iridium satellites being good examples).  So as Harb says there might not be much we could do about it.  The only idea I can think of is that maybe it's possible to put an anti-reflective coating on solar panels, similarly to the anti-reflective coating that is put on some optics or eyeglasses.  But I don't know if that's practical for a solar panel, and it probably would not be cheap.

HarbingerDawn wrote:
Source of the post The Sun radiates most strongly in visible light, so absorbing that while reflecting IR wouldn't do any favors for thermal management.

Yes, this is a problem.  Actually the better idea would be to absorb the infrared rather than reflect it.  A good reflector is a poor emitter, so a good reflector of infrared and absorber of visible light would heat up until it glows visibly red.  Obviously not good.  But a good absorber is a good emitter, so a material that absorbs both visible and infrared would cool itself better by re-radiating that energy in the infrared.

Problem: the equilibrium temperature this would reach is still very high.  If it is a perfect absorber and emitter of all radiation, then in sunlight the temperature would climb to around 120°C.  This can be reduced by spinning the satellite (like the Passive Thermal Control state during Apollo's translunar coast), but only if that doesn't interfere with the satellite's function.

This is why most satellites are bright and reflective.  It's easier to keep something cool by having a large albedo than to have a high emissivity.
 
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28 May 2019 00:34

But, it's really only one side of the satellite that needs to be near invisible in visible light, the side that receives the least sunlight as the Earth is blocking in that direction.  So how bad can it be?  I think most satellites have the same side facing the Earth.  In some cases when this doesn't work, some kind of screen could.  It should only be satellites doing optical observations of Earth that need to be visible from the ground.

It sounds like an engineering problem, which nobody has fixed simply because nobody has been told that it actually is an issue.
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28 May 2019 00:55

The Earth isn't blocking the Sun from the satellite if the satellite is shining in the night sky.  A large area of the satellite that is visible from Earth is also in direct sunlight for a significant time (depends on altitude, inclination of the orbit, and the time of year.)  This is especially problematic for high inclination or polar orbits -- the very same satellites that contribute the most pollution to the night sky.

It probably is just an engineering problem, and it warrants thinking about.  It's certainly a nuisance; I notice it a lot at my latitude and satellite flares can even interfere with professional astronomical observations.  But I don't think it's very simple to solve.  I think the light pollution from our expanding urban areas is much easier to solve, yet little is being done about it outside of a few places acting as role models. :(   We need more awareness.
 
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28 May 2019 01:52

I am all aware of light pollution problems, the issue is hardly anyone cares and all in the name of progress.

I have slowly watched my skies give in to the light from the city 100Km away and what was true dark skies as a kid now is a wash of light for a large portion of it.  Makes me mad that despite awareness the city councils don't care and continue to install fixtures and more lights that spew light in all directions for no good reason. Often the very lights make it hard to see at night while driving because they introduce glare.
 
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28 May 2019 14:29

They probably would get interested really fast if they knew that light pollution increases cancer risks by around 15-20%
 
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28 May 2019 19:29

A-L-E-X wrote:
They probably would get interested really fast if they knew that light pollution increases cancer risks by around 15-20%

Source please.
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28 May 2019 21:43

My point was that when satellites are in sunlight (and the ground below is dark), the sunlight falls at the surface facing Earth at a shallow angle, so the heating problem is less if the albedo for that surface is reduced.

Scott Manley just covered this topic.

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03 Jun 2019 12:26

Stellarator wrote:
A-L-E-X wrote:
They probably would get interested really fast if they knew that light pollution increases cancer risks by around 15-20%

Source please.

It has to do with light pollution making it more difficult to sleep at night and interfering with the release of melatonin which in turn causes an increase in breast and prostate cancer because interfering with the release of melatonin is connected to cell proliferation.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3002207/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5454613/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2627884/
http://darksky.org/study-links-artifici ... ncer-risk/
https://www.darksky.org/light-pollution/human-health/
http://theconversation.com/harvard-stud ... ight-75171
https://earthtalk.org/light-pollution-breast-cancer/
“Light at night is now clearly a risk factor for breast cancer,” says David Blask, a researcher at the Cooperstown, New York-based Mary Imogene Bassett Research Institute. “Breast tumors are awake during the day, and melatonin puts them to sleep at night,” he adds.

Epidemiologist Richard Stevens of the U.S. Department of Energy’s Pacific Northwest National Laboratory first discovered the link between breast cancer and light pollution in the late 1980s. Stevens found that breast cancer rates were significantly higher in industrialized countries, where nighttime lighting is prevalent, than in developing regions.

Lending credence to Stevens’ research are the findings of another researcher, William Hrushesky of the South Carolina-based Dorn Veterans Affairs Medical Center, who discovered that female night shift workers have a 50% greater risk of developing breast cancer than other working women. He also found that blind women have high melatonin concentrations and unusually low rates of breast cancer.

To reduce breast cancer risks from light pollution, Prevention magazine recommends nine hours of sleep nightly in a dark room devoid of both interior (computer screens) and exterior (street lamps) light sources. A study of 12,000 Finnish women found that those who slept nine hours nightly had less than one-third the risk of developing a breast tumor than those who slept only seven or eight hours. Even bright light from a trip to the bathroom can have an affect, so dim nightlights are recommended for night lighting.

Light pollution causes other problems besides increased cancer risks. According to the Sierra Club, birds and animals can be confused by artificial lighting, leading them away from familiar foraging areas and disrupting their breeding cycles. And the photosynthetic cycles of deciduous trees (those that shed their leaves in the fall) have been shown to be disrupted due to the preponderance of artificial nighttime lights.

Another environmental impact of excessive use of artificial light is, of course, energy waste. The International Dark-Sky Association computes that unnecessary nighttime lighting wastes upwards of $1.5 billion in electricity costs around the world each year while accounting for the release of more than 12 million tons of carbon dioxide, the leading greenhouse gas, into the atmosphere. Individuals can do their part by keeping lights dim or off at home at night—and convincing their employers and local government offices to do the same.
 
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05 Jun 2019 05:01

A-L-E-X wrote:
Source of the post To reduce breast cancer risks from light pollution, Prevention magazine recommends nine hours of sleep nightly in a dark room devoid of both interior (computer screens) and exterior (street lamps) light sources. A study of 12,000 Finnish women found that those who slept nine hours nightly had less than one-third the risk of developing a breast tumor than those who slept only seven or eight hours. Even bright light from a trip to the bathroom can have an affect, so dim nightlights are recommended for night lighting.

In a country like Finland where nights don't get dark during summers, a trip to the bathroom ought to be insignificant compared to the light coming through the bedroom windows (even with good curtains/blinds).  It rather sounds like uninterrupted sleep is what matters (which disturbing lights can affect).

I have a streetlight pretty close to my bedroom window.  Only a totally insignificant amount that light gets past the curtains compared to the amount of natural light getting through during the summer nights.  It doesn't have to be completely dark.  I sleep with my eyes shut.
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05 Jun 2019 13:10

Living close to NYC absolutely sucks.  There is a post office that is across the street from me which strobes a bright light in its parking lot that can be easily seen from one corner of my house to the other.  It's really bright.  There's also an airport close by and airplanes fly really close and their lights can easily be seen too.  All kinds of lights- from LEDs to orange mercury vapor lamps. I read about the danger for eyesight from LEDs too.

In my other house in the Poconos it gets completely dark and quiet at night and I notice I sleep far deeper and far more quickly- as if I've been drugged lol.  I'm convinced that the high stress levels and unhealthy urban life that causes people to take sleeping pills (which have their own side effects) or antidepressants or antianxiety meds is directly linked to our unhealthy lifestyle.  Here near the city I can never sleep more than 2-3 hours before waking up, in the Poconos Mountains I can sleep 10 straight hours and wake up the next morning and not even feel like 10 minutes passed by!  But I always feel far more refreshed and relaxed and my blood pressure is lower there and the air is far cleaner.
 
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Light pollution

06 Jun 2019 00:54

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Light pollution

07 Jun 2019 20:50

Light pollution is getting worse. Years before most of street lightings are fluorescent or sodium. Which can easily be filtered by an UHC filter. However today more and more lightings are LED that have wide spectrum.

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