Why can't you see the stars at night?
There are two main reasons that you can't see the stars in a bright city: 1) If you look at the bright lights, then your pupils contract and let less light into your eyes. This causes you to not be able to see things that are dim - like stars. This is why astronomers have to let their eyes "dark adapt" before observing through a telescope. It is also why when you go to bed, right after you turn off the light you can't see anything, but an hour later if you wake up, the room seems brighter - your pupils have dilated. 2) The bright city lights also shoot light UP into the sky. Some of this light bounces off of the dust and water molecules into the air, which scatters them and makes the background of the sky look brighter and brighter. If the atmosphere is bright enough, you won't be able to make out the stars that are shining behind it.
Why is it hard to see the stars at night and what can we do about it?
It's actually a combination of light and air pollution. Normally around cities and even in the suburbs there are street lights, traffic, malls, stores, all kinds of things that put off light. This ambient light tends to illumnate any pollution, fog, clouds or anything else in the area. The result is, unless it's a very clear day most of the dimmer stars ( either because they are smaller or because they are further away ) are more difficult to see. If you go to the mountains where air pollution is minimal, less humid air, less clouds, and there is less ambient light from cities even the dimmest stars are clearly visible. Thats one reason they put observatories way up on mountains usually. The main things you should research and write about in your essay is what we can do about it would probably be to reduce light pollution and reduce air pollution. Air pollution is tied into carbon dioxide emissions, which you should be able to find 1000s of articles about given all the talk of global warming. See the links below to get you started in your research.
Why do the moon and stars come out at night?
The existing answers here are pretty good, I just wanted to add a bit of biology to it.So as covered in other posts, the moon and stars are “out” during the day, you just can’t see them because when the sun is out, it’s too bright to see the stars. (You can see the moon, the moon is visible in the day for almost half of the time and only appears to “vanish” entirely for a few days a month during the new moon phase)But why? Why can’t you see dim things when you have a bright source?The answer is in how your eye makes an image: Light from an object comes into your eyes, passes through the pupil, and strikes a light-sensitive cell on the back of your eyeball. The angle it comes in at (and therefore the direction of its source” determines the cell it hits, which your brain extrapolates to form an image. The fainter the light, the less stimulation there is, and the less your brain “reacts” to it. If you want to intensify that faint source, you have to let in more light, which means your pupil needs to get bigger.Now, if you spend awhile in the dark, you notice your eye “adjusts” to the dark. But what’s actually going on is the iris of your eye contracts, widening the hole of the pupil to let in more light. But if it did that when you were looking at something bright, too -much- light would get into your eye, and the photo cells in the eye would get burned out. So we have a defense mechanism. If something bright hits our field of vision, our pupil contracts, protecting our eye. In order to allow us to see better in darkness, our pupil has to widen, but to keep our eyes safe in the day, it takes time for that to happen. Imagine if every time you blinked, you felt that flash of disorienting brightness you get from walking out into the sun from a dark room. So our pupils contract very quickly to protect our eyes, but take time relaxing.So what does this have to do with stars? Well, stars are relatively very faint. So to gather enough light to resolve an image would require widening our pupils, but during the day, our eyes can’t do that or they’d be damaged by the bright sunlight.So you can only see stars after your eyes have experienced nothing but darkness for a long time.This is also why you can’t see many, if any, stars when you’re in a city with lots of lights, or standing underneath a street light.
How does the moon reflect sunlight?
Hello fella,First a question, why moon shines?The answer is simple and well known that moon shines because it reflects the light coming from sun.Now here is your doubt that why does moon reflect light even if it is a rock.You are correct that moon is rock and they are not so much reflective, but we are not talking about mirror or an ice shiny surface.Every surface reflect some portion of sunlight and so does moon. Now you may think that it's OK that moon reflect light but why does it appears self luminous.Explanation:The ratio of reflected radiation from the surface to incident radiation upon a body is called albedo.Its dimensionless nature lets it be expressed as a percentage and is measured on a scale from zero for no reflection of a perfectly black surface to 1 for perfect reflection of a white surface..Albedo:wiki (see astronomical albedo where you can get other links also) In layman its measure of reflectivity of an object and study of albedo of celestial bodies can be used to infer about their properties.Moon has albedo of 0.12 but moon reflection is strongly directional displaying strong opposition effect.While the opposition effect is the brightening of a rough surfaces, when illuminated from directly behind the observer due to which light coming from them appears more bright as phase angle of observation approaches zero.Therefore, rather being made of rock and having low albedo the moon has a strongly directional and non-Lambertian reflection accompanied by opposition effect.But after googling all this I was still not very much convinced so I decided to conduct a small experiment using some rocks and LED light.So what I did was, brought a rock and illuminated it directly with LED light.As it was expected the rock seemed glowing and reflecting light.Being a rock it was illuminated by LED which may answer your query.Now if I get close and change the phase angle.It does not appear illuminated, the same case when astronauts see moon.But in reality the moon is very big and the source that is sun is massive as a result huge, huge amount of light is incident on moon, therefore the moon reflects enough light to appear luminous.
If the Moon does not have its own light, how are we able to see the moon?
It’s the same reason we can see any objects that aren’t their own light emitters: reflection. Take an apple, for example. An apple isn’t a light emitter. It doesn’t make it’s own light. So how can you see an apple? Because light from the Sun hits the apple, and most of that light is absorbed by the apple, but some of that light is reflected off of the apple and into your eye, allowing you to perceive and see the apple.The same thing is happening with the moon. Even though it doesn’t create it’s own light, light from the Sun is hitting it and some of that light is bouncing off and getting reflected back to Earth.And the moon isn’t actually even white, it’s actually a dark, dark grey, similar to the color of asphalt, and it doesn’t even reflect that much light back to us, only 10% or so.But that 10% reflection is enough for us to see it, and quite brightly at that, as it’s the brightest object in our night sky due to its proximity to Earth.
Why does the moon not have its own light?
Oh, but it does.Everything* has its own light — as long as it is held above absolute zero.Almost nothing in this universe is a perfect “black body” — but a lot of things come fairly close, so quite often we model everything as being one of these 'black bodies'.This simplifies the mathematics, and means that Planck’s law can be used as an approximation.Planck’s law tells us the amount of energy that an object emits at a given wavelength:[math]B (\lambda, T) = \frac{2 h c^2}{\lambda^5} \frac{1}{e^{\frac{hc}{\lambda k_B T}} -1 }[/math]Now, if you plot this for several temperatures, you end up with something that looks like this:Now, for these things to emit visible light, they need to get really, really hot.The sun is really, really hot — and so it emits loads of light in the visible spectrum.The Moon, on the other hand is really cold — its surface temperature varies wildly, but averages out at about 200K.This means that the peak wavelength of the Moon’s emission spectrum occurs at: 13 micrometres.This is deep into the infrared spectrum, which our eyes cannot detect.Everything in the universe glows (roughly) according to this law — you and I glow at around 10 micrometers — the sun glows at the much hotter temperature of 500nm (yes, I am expressing temperatures in wavelengths — problem?).So the Moon does have its own light.It is just very, very dim, and very, very infrared — and thus is far outweighed by the reflected light from the sun!“Everything” here meaning “normal matter” — this does not include dark matter. In fact, the lack of radiation from dark matter is exactly why it is called dark.