If you were staring to the sky in a big city and electricity is turned off in a big area around you, would you be seeing the sky with little light pollution instantly?
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If all the lights in a city, and the area surrounding it were shut off. How long would it take for the light pollution to clear, so the light from stars could be seen?
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This is the Milky Way above Kakadu National Park, Australia, and my first try at astrophotography.    Thirty second exposure, f/4.0 at 17mm with ISO 12800 (!!) which in hindsight probably was way too high and resulted in a lot of noise. I also used Picasa to increase contrast, but I probably went a bit overboard there as well.  , I am looking for input on how to better postprocess this picture to reduce noise.
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We have solar panels and mains power. Last night was very windy; we heard quite a few bangs from outside and thought it might be the wires getting knocked together. Woke up this morning and we have power to everything except the lights and our stove. We have a smart meter and it has no pulse light. What do you think could be the problem. Is it a main fuse coming into house before the meter?
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I am not talking about mirrors, just a plain window made of glass like material. Would it be possible to allow light pass only in one direction but not the other?
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Many articles on the internet write about melatonin and its effects, making you tired. A lot of articles also point out how the use of devices before going to bed in modern days likely decrease melatonin production. Therefore, making it harder to fall asleep. But this information is only about the process of getting to sleep, before we are actually sleeping.  A recent Harvard Medical article 1 states:     High exposure to bright, artificial outdoor lights during the night may result in sleepless nights for older adults.   Referring to a publication on Nov. 15, 2018, in the Journal of Clinical Sleep Medicine.  Considering that:    many people nowadays, use their mobile devices in bed prior to going to sleep; modern cities or houses have (street) lights that are always enabled at night; ignoring the phase of falling sleep; focusing only on the time we are asleep already, so during the actual sleep cycles.   Does a darker room with less or no (artificial) light pollution improve sleep quality, with all associated health benefits as a result? In other words: Does light pollution, while asleep decrease the sleep quality or does light pollution only negatively affect the phase of “falling asleep”?  I wasn't able to find any studies or information regarding sleep quality in relation to light pollution during sleep. Were such studies performed? Are there specific moments when light pollution affects sleep quality the most, for example during REM-sleep or in a specific sleeping phase?    1
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I was just wondering why Fresnel Lenses are not widely used in the production of solar electricity. Their use there would mean that you could produce heat within a fraction of a second, up to a few minutes and run a turbine to produce electricity.  Though it is used in welding, I am not sure what are the problems in producing electricity, as stated by :     New applications have appeared in solar energy, where Fresnel lenses can concentrate sunlight (with a ratio of almost 500:1) onto solar cells.
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By analogy with the sun, whose light is apparently reaching us in 8 minutes, it means that we are only viewing the sun 8 minutes ago when we look up at it. However, what if we were eventually able to build powerful machines that could view light from say hundreds/thousands of years ago, wouldn't that mean we would be able to observe what anyone did at any given time (given that we know their rough whereabouts at that time, e.g. where they lived). I think this is more a question of: Do things we can observe die out immediately, or travel as light, or get stored somewhere?  (Sorry, I know next to nothing about Physics so please cut me some slack if I said anything naive/silly)
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I'm curious what will happen if we 'drive' a car with (almost) the speed of light, and all of sudden we switch the car headlights on? Will the car headlights ray have double speed (speed of 600.000km/h) or that ray will never be seen?
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I've been wondering this for a while.  Why is there no electricity in the post apocalyptic world?
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Since we see the  at least once in a month when the Moon gets in between of the Sun and the Earth during the evening ( and as far as I know if this happens during the day, you'll get to see a . Why don't we get to see this often or in the day?   Does it mean that in some part of world there's a solar eclipse when we are seeing a new moon? I'm looking for a diagram or interactive way to understand this if possible as I'm not a native English speaker, but I'll try my best to do so.
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A  is formed when a raindrop refracts light, but why then does the whole sky not become a huge rainbow when it rains? Would the light not be dispersed into ordinary white light? What causes it to look as if each end is nearly touching the ground?
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A photon emitted from a receding source (Doppler redshift) has less energy when detected at an observer's location. Please explain the energy loss from the perspective of energy conservation.
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I, like everybody I suppose, have read the  why the colour of the sky is blue:     ... the two most common types of matter present in the atmosphere are   gaseous nitrogen and oxygen. These particles are most effective in   scattering the higher frequency and shorter wavelength portions of the   visible light spectrum. This scattering process involves the   absorption of a light wave by an atom followed by reemission of a   light wave in a variety of directions. The amount of multidirectional   scattering that occurs is dependent upon the frequency of the light.   ... So as white light.. from the sun passes through our atmosphere,   the high frequencies become scattered by atmospheric particles while   the lower frequencies are most likely to pass through the atmosphere   without a significant alteration in their direction. This scattering   of the higher frequencies of light illuminates the skies with light on   the BIV end of the visible spectrum. Compared to blue light, violet   light is most easily scattered by atmospheric particles. However, our   eyes are more sensitive to light with blue frequencies. Thus, we view   the skies as being blue in color.   and why sunsets are red:     ... the light that is not scattered is able to pass through our   atmosphere and reach our eyes in a rather non-interrupted path. The   lower frequencies of sunlight (ROY) tend to reach our eyes as we sight   directly at the sun during midday. While sunlight consists of the   entire range of frequencies of visible light, not all frequencies are   equally intense. In fact, sunlight tends to be most rich with yellow   light frequencies. For these reasons, the sun appears yellow during   midday due to the direct passage of dominant amounts of yellow   frequencies through our atmosphere and to our eyes.      The appearance of the sun changes with the time of day. While it may   be yellow during midday, it is often found to gradually turn color as   it approaches sunset. This can be explained by light scattering. As   the sun approaches the horizon line, sunlight must traverse a greater   distance through our atmosphere; this is demonstrated in the diagram   below. As the path that sunlight takes through our atmosphere   increases in length, ROYGBIV encounters more and more atmospheric   particles. This results in the scattering of greater and greater   amounts of yellow light. During sunset hours, the light passing   through our atmosphere to our eyes tends to be most concentrated with   red and orange frequencies of light. For this reason, the sunsets have   a reddish-orange hue. The effect of a red sunset becomes more   pronounced if the atmosphere contains more and more particles.   Can you explain why the colour of the sky passes from blue to orange/red skipping altogether the whole range of green frequencies?  I have only heard of the legendary 'green, emerald line/ flash'     that appears in particular circumstances     Green flashes are enhanced by mirage, which increase refraction... is more likely to be seen in stable, clear air,... One might expect to see a blue flash, since blue light is   refracted most of all, and ... is   therefore the very last to disappear below the horizon, but the blue   is preferentially scattered out of the line of sight, and the   remaining light ends up appearing green   but I have never seen it, nor do I know anybody who ever did.
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I took a picture once in a beautiful location with an awesome background, and a cool location to get the shot. The problem is, the location of the subject had substantially less light then the background, giving a silhouette effect. Without using an external flash, and on a low budget, what could I do to improve this picture?  Specifically, I shooting with a DSLR, outdoors. The DSLR has a small pop-up flash. The nearest good light source was maybe 5-10 feet away.   Thanks guys!    How do I avoid a dark subject when there's bright sunlight from windows?  by   I recently shot some photos at a friend's wedding. The location was lovely with lots of light — sometimes too much. The sunlight from the windows and skylights seemed to overpower the shot and the subject/people were very dark. What are some ways to avoid this without using fancy equipment? (I'm just starting out, I'm not a wedding photographer or anything!)  Here is one example I took — and this is after I've lightened it somewhat with Picasa:    I'm using a Nikon D5000 with a standard 18-55mm lens.
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I have noticed that if you look directly at tubelight (I have only white ones in my home) and close your eyes little, you see little random shaped colourless things sometimes with slow speed and sometimes with falling down.   They are shaped like circles with something in between and in chains of random length.   My father has also seen them. So, I am sure I am not imagining things. What the hell are they?
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I'm trying to do long exposure photos with car headlight trails and am finding the results a little disappointing due to the low 'impact' of the light trails.  I believe there are a few things affecting this, namely   length of exposure (currently limited to about 90s at min ISO and aperture) the amount of traffic the level of light given off by street lamps   I believe 1 &amp; 2 can be fixed by the addition of an ND filter and choosing a busier time to take the pictures, but am not sure how I can address 3.  Is there some sort of filter I can use which will minimise the effect of the street lamps without cutting out too much of the light from car headlamps/tail lamps?  Here's an example of what I've done so far:
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Before you all jump in with 2.73 K or thereabouts, this is more of an experimental question. It will obviously depend on humidity and radiation being scattered back towards the surface of the Earth. Any ideas? Anyone ever pointed a pyrometer or similar at the night sky?