ChatterBank4 mins ago
Sunset
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Hope this is the right place for this. If it takes approximately 8 minutes for the light from the sun to reach us and I am watching the sun set, did the sun actually set 8 minutes ago?
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The atmosphere bit is relevant of course but i think really the questioner had in mind what physicists call a thought experiment so it's dsigned to make you think disregarding trivia that occurs because be have an atmosphere. It's like when you stand on the roof of a train and jump up will you land in the same place? yes you will but some numpty will always say yeah but the air resistance means that you land a millimeter backwards, yes yes yes but that detracts from the point of the question.
With regard to the sunset situation I'll try and explain so that people as dim as KnobKnot can grasp it. The light from the edge of the sun you see started travelling when it was 8 minutes away from the horizon. The earth rotated in between a litle bit. Get it kn0bhead?
With regard to the sunset situation I'll try and explain so that people as dim as KnobKnot can grasp it. The light from the edge of the sun you see started travelling when it was 8 minutes away from the horizon. The earth rotated in between a litle bit. Get it kn0bhead?
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read the question again numpty ...... did the sun actually set 8 minutes ago?" I said NO and even explained it for your single celled intellect even a tw&t like you can grasp that. I resent your attempts at a 1 word put down because you are found wanting in the reasoning department. Bollux?? if you must but I think the OP would conclude that I have at least attempted an answer rather than an ill chosen sound bite. robknot? yes I think you probably are! too easy!
OK, I'm not an astronomer or mathematician, but the way I look at the question is this. And the times I use are assuming that light does take 8 mins to travel from teh sun to the earth.
If I nip out at midday and look at the sun, the image I see is the sun as it was 8 mins earlier. Similarly, if I'm sitting on a beach watching the sunset, when the trailing edge of the sun goes below the horizon (and yes I am ignoring the atmospheric effect here) I' m seeing what the actual sun did 8 minutes earlier.
Now as the atmosphere makes the image of the sun I see at sunset appear higher in the sky than it actually is, I'd say that when I see the edge of the sun dip below the horizon what I am seeing actually happened more than 8 minutes earlier (meaning that the actual sun dipped below the actual horizon more than 8 minutes before I see it happening. How much longer before would depend on how much higher the sun appears due to the effect of atmosphere - somewhere around 4 mins for every degree).
If I'm wrong, would someone like to explain in a way that would be suitable for a moderately intelligent child to understand ?
If I nip out at midday and look at the sun, the image I see is the sun as it was 8 mins earlier. Similarly, if I'm sitting on a beach watching the sunset, when the trailing edge of the sun goes below the horizon (and yes I am ignoring the atmospheric effect here) I' m seeing what the actual sun did 8 minutes earlier.
Now as the atmosphere makes the image of the sun I see at sunset appear higher in the sky than it actually is, I'd say that when I see the edge of the sun dip below the horizon what I am seeing actually happened more than 8 minutes earlier (meaning that the actual sun dipped below the actual horizon more than 8 minutes before I see it happening. How much longer before would depend on how much higher the sun appears due to the effect of atmosphere - somewhere around 4 mins for every degree).
If I'm wrong, would someone like to explain in a way that would be suitable for a moderately intelligent child to understand ?
Huderon, In my estimation your answer is spot on. Nevertheless, here�s mine:
Setting aside for the moment atmospheric effects: In the ~8.3 minutes time required for light to travel from the Sun, the Earth rotates about two degrees on its axis. In relation to an observer at a fixed position on the surface of the rotating Earth, the Sun�s actual location would be about 4 solar diametres further along its apparent path of travel (in a westerly direction) from its apparent position in the sky.
Light penetrating the atmosphere at an angle is refracted to varying degrees towards the Earth�s surface. Consequently the Sun appears further above the horizon and to rise sooner and set later than it would if not for atmospheric refraction.
By definition sunset refers to the time coinciding with the visual disappearance of the Sun below the horizon without consideration for where the Sun is actually located in space.
Setting aside for the moment atmospheric effects: In the ~8.3 minutes time required for light to travel from the Sun, the Earth rotates about two degrees on its axis. In relation to an observer at a fixed position on the surface of the rotating Earth, the Sun�s actual location would be about 4 solar diametres further along its apparent path of travel (in a westerly direction) from its apparent position in the sky.
Light penetrating the atmosphere at an angle is refracted to varying degrees towards the Earth�s surface. Consequently the Sun appears further above the horizon and to rise sooner and set later than it would if not for atmospheric refraction.
By definition sunset refers to the time coinciding with the visual disappearance of the Sun below the horizon without consideration for where the Sun is actually located in space.
OK. I really didn't want you all to fight over me. Your answers were all very interesting and i have have concluded that the answer to my question is YES. However, i'm beginning to wish I hadn't asked as I don't really understand any of your answers. This was not a "thought experiment". I really wanted to know. thanks anyway.
Regardless of where the Sun may actually be in space, If you draw your pistol before the last ray has disappeared below the horizon . . . that's cheating!
In the sense you meant the question Francis, the answer is yes, though the time the sun set is probably closer to 15 mins earlier than we see it than the 8 mins. or so that it takes light to travel from the sun to Earth. That's because our atmosphere bends the light from the sun and makes us see the sun slightly higher in the sky than it actually is.
Technically, sunset is when we see the trailing edge of the sun (the top bit) disappear below the horizon, so in that sense the answer would be no.
Technically, sunset is when we see the trailing edge of the sun (the top bit) disappear below the horizon, so in that sense the answer would be no.
Yes, sunset is when we SEE the last bit of the sun disappear below the horizon.
That's true even though, because of the time it takes light to travel here from the sun, and because our atmosphere bends the light and makes the sun appear slightly higher in the sky than it is at that time of day, at the time we see the sun drop below the horizon, the sun has already been below it for a while.
That nice reddish disk of the sun we see at sunset is actually an illusion, a mirage caused by our atmosphere. If you were watching the sun go down and at the halfway point someone suddenly whipped the atmosphere away, you'd see the sun setting one moment and no sun the next, because the sun is already below the horizon when we are witnessing it go down. That's why sunset is when we SEE the last bit of the sun disappear below the horizon regardless of where the sun actually is in relation to whoever is watching it set.
That's true even though, because of the time it takes light to travel here from the sun, and because our atmosphere bends the light and makes the sun appear slightly higher in the sky than it is at that time of day, at the time we see the sun drop below the horizon, the sun has already been below it for a while.
That nice reddish disk of the sun we see at sunset is actually an illusion, a mirage caused by our atmosphere. If you were watching the sun go down and at the halfway point someone suddenly whipped the atmosphere away, you'd see the sun setting one moment and no sun the next, because the sun is already below the horizon when we are witnessing it go down. That's why sunset is when we SEE the last bit of the sun disappear below the horizon regardless of where the sun actually is in relation to whoever is watching it set.
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