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Why is sunrise less red than sunset?

  1. May 22, 2004 #1
    Why is sunrise less red than sunset?

    after all .... its the same sun ... same earth .... only moving up one time and down another time?
     
  2. jcsd
  3. Jun 10, 2004 #2
    the only guess I would have is something along the lines of red shift and blue shift. A shift in the electromagnetic spectrum. The Earth is spinning in one direction. The light at sunrise is traveling at a different speed in comparisan to the speed of light at sunset. That would be my semi educated guess. Don't take my word for it, because I'm probably wrong. Most people probably don't understand what I'm trying to say because I did a horrible job at communicating it.
     
  4. Jun 10, 2004 #3

    Ivan Seeking

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    If in fact it is, [do you know this for a fact?] then I would say that humidity, temperature, and particulates in the air make the difference. Really smoggy Los Angeles summer evenings can actually make for some beautiful sunsets...in a way...sort of... :biggrin:
     
  5. Jun 10, 2004 #4
    It all depends on the atmosphere between you and the sun. I can't think of any inherent reason this would be true for all viewers.

    It's quite possible there is more/thicker atmosphere in one direction where you are - if the sunrise is over mountains, for example, then the thinner atmosphere and larger angle means there will be less Rayligh scattering. Sunset over the ocean minimizes the angle and gives you more scattering.
     
  6. Jun 10, 2004 #5

    Gokul43201

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    I understand what you're trying to say. Unfortunately, the change in relative velocity between the Earth and Sun from dawn to dusk, is negligible compared to the speed of light. So the wavelength shift will also be negligible.

    It would certainly seem to be an atmospheric effect. The more dust and particulate matter you have in the air, the redder is the light. So, when is there more dust around...at dawn or dusk ?

    Perhaps too simplistic but may be accurate to first order, what ?
     
  7. Jun 10, 2004 #6

    Janitor

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    Just a thought, but in places I have lived, human activity is higher in the daytime (tractors and autos kicking up dust, for example), and it tends to be windier in the daytime as far as I can tell, due to solar energy stirring up the atmosphere. So there are probably more particulates sent into the air during the daylight hours. Maybe a dozen or so hours of relative peace and calm overnight are enough to let a good bit of that crud settle back down to the ground, leaving a cleaner atmosphere at sunrise.
     
  8. Jun 10, 2004 #7

    Hurkyl

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    Don't forget that the sun rises "over" cold air and sets "over" warm air. I would presume that this is the most important factor, unless this is simply psychological.
     
  9. Jun 11, 2004 #8
    quddusaliquddus
    Embarassing activities tend to occur more often toward dusk than dawn.

    Really, blame it on smog.
     
  10. Jun 13, 2004 #9

    Ivan Seeking

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    From here
    http://www.mic-d.com/curriculum/lightandcolor/colortemperature.html

    we have this source to black body radiator temperature chart. This effectively tells us the color of the source indicated according to the color of a black body radiator held at the same temp. Note that Sunrise and Sunset are shown as the same.

    Daylight Sources Color Temperature (K)

    Skylight 12000 to 18000
    Overcast Sky 7000
    Noon Sun/Clear Summer Sky 5000 to 7000
    Noon Sun/Clear Winter Sky 5500 to 6000
    Photographic Daylight 5500
    Noon Sunlight
    (Date Dependent) 4900 to 5800
    Average Noon Sunlight
    (Northern Hemisphere) 5400
    Sunlight at 30-Degree Altitude 4500
    Sunlight at 20-Degree Altitude 4000
    Sunlight at 10-Degree Altitude 3500

    Sunrise and Sunset 3000

    Artificial Sources Color Temperature (K)
    White LED 6500 to 9500
    Electronic Flash 5500 to 6500
    Xenon Burner 6000
    White Flame Carbon Arc 5000
    Warm White Fluorescent Tubes 4000
    Aluminum-Filled Flash Bulbs
    (M2, 5, & 25) 3800
    500-Watt 3400 K Photoflood 3400
    12 Volt/100 Watt
    Tungsten-Halogen @ 9 Volts 3200
    12 Volt/50 Watt
    Tungsten-Halogen @ 9 Volts 3200
    100-Watt Household Lamp 2900
    40-Watt Household Lamp 2650
    Gaslight 2000 to 2200
    Candlelight
    (British Standard) 2900

    I wasn't sure whether or not this accounts for atmospheric variations.

    I found this:
    http://www.physics.isu.edu/weather/kmdbbd/notesc4.pdf
     
    Last edited: Jun 13, 2004
  11. Jul 23, 2004 #10
    Theory of Reltivity demystified (long winded, but can't be helped)

    I decided I had to write about this, because this is an obvious misuse of the Theory of Relativity, and people where starting to use this reasoning. It also should be noted that this "theory" has been validated in experiments (to the best of our ability) to be true.

    I think I get what your trying to say, and I think your almost there, but your missing something crucial. The Theory of Relativity tells us that the speed of light can never be perceived to be faster or slower depending on our relative speed. To give an example,
    Say you are in a car moving at 100 mph and you have a gun that can shoot bullets going at a constant speed of 300 mph. Normally, if you shot the gun straight ahead in the same direction that the car is moving, the bullet velocity would could be calculated by adding the two velocities (ignoring air resistance) together. So the bullet will now be traveling about 400 mph (100+300mph). Adversely, if you shot the gun in the opposite direction of that the car is traveling, then the speed of the bullet will be 200 mph in the opposite direction that the car is moving (hence, -200mph, taking the direction of the car to be the positive direction).

    Now, here's the difference, Relativity tells us that this logic breaks down at speeds close (er) to the speed of light (approx 670 Million mph). To emphasize, say now we are in a space ship traveling 100 Million mph. We now have a space gun (which physical bullets (ie. having mass)) that can shoot a bullet traveling 300 Million mph. If we shoot the bullet straight ahead of the ship going in the same direction. The velocity of the bullet is not 400 million mph. You can not add the two velocities like this anymore. The obvious reason being, suppose you were now on a space ship traveling 500 million mph. If you take out your gun and shoot a bullet traveling straight ahead, and simply added up the velocities of the bullet and space ship, you would find that Low and Behold, that bullet would be traveling at 800 Million MPH, that would be faster than light travel. This cannot happen. An object cannot travel faster than the speed of light. The theory of relativity says, instead, Time will slow down and length will elongate. Therefore, speed (measured in distance over time) would always be less than that of the speed of light.

    (okay, almost finished)

    Now to wrap it all up with what this has to do with the statement quoted above. The special Theory of Relativity defines that an object cannot go faster than the speed of light. But Light, obviously, can travel at the speed of light (and all electromagnetic waves). However taken the above example about launching a projectile at already high speeds, will not cause an object to exceed the speed of light. But how about, using a beam of light instead of a projectile? The question asked is, could, this "Beam" of light projected from a space ship moving at 100 Million MPH, go faster than the speed of light (670 Million MPH). If this question doesn't seem right to you, congratulations, you understand. Light cannot go faster or slower than the speed of light. Light will continue to travel at (670 million mph). Regardless of whose reference frame your in (ie. on the space ship, on earth, or floating in space) the light will continue to appear to be traveling at 670 million mph because of the theory of relativity (because the closer you are to the speed of light, the more time will slow down (from the point of view of some one not on the space ship) (so time will appear to speed up from a point of view on the space ship, and hence light will appear to be traveling 670 million mph away from you, regardless of your speed).

    So, in regard to what was said that the rotation of the earth makes the light faster or slower, depending if you are rotating away or towards the sun, this would have no effect. And to the other reply that was made toward this quote, about this quote, saying that the speed is negligible, compared to the speed of light, and that’s why it has nothing much to do with it, that is not true. The rotation of the earth could be 500x faster and (because of relativity) this would not make the light speed up or slow down.

    If you think about our expanding universe and how they measure distance in light years, it starts to make sense that if light actually could speed up or slow down, then we could not measure distance in terms of light years.

    Also note, you may be thinking, wait, light can Slow down. This is true, the speed of light will ONLY slow down as it passes through a denser medium. So light travels slower in water than in air and slower in air than space, but light is its fastest through a vacuum. There is a substance, if anyone is interested, called "Slow Glass" it is essentially, a transparent material that can slow light down so much that it can take light minutes to pass through 4 inches of this material. Science is working on extending this delay to years!

    I do however, think I know what this sender may be referring to. The Doppler effect, essentially, may be a strong competitor in the reason why the sun is more red in a sunset. We experience the Doppler effect everyday, when a firefighter's siren goes off, when it is approaching, the pitch is high, and when the siren is moving away from us, the pitch gets considerably lower. This also works with electromagnetic waves. If you ever wondered why scientists came up with a big bang theory, this is a big part of it. We can see, by listening to the stars, that light waves are perceived to be microwaves because the universe is expanding away from us. (This is also how police use radar guns to pick up speeders).

    I heard on the radio today that their answer was that there is more dust in the air in the evening. And that is the reason why. I dislike their reasoning, but perhaps, it is partially true (however, I've seen sunsets on the pacific, and they are just as red, so, take it as you may). Perhaps the extra dust reflects more of the blue spectrum of light (the reason why the sky is blue and the moon is orange on the horizon at times) and causes the sun to appear redder. Perhaps, upon further thought, this has more truth behind it, because often the sky appears to be violet around the sunset. Perhaps a little bit of additional light (red light) is being reflected as well and causing it to appear purple.
     
    Last edited: Jul 23, 2004
  12. Jul 23, 2004 #11

    Njorl

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    Along these lines, the sunset is viewed through air that has been illuminated all day. Illumination affects the chemistry of air. Warm air is also more likely to contain humidity. I know here in DC, we get thunderstorms just after sundown as the air cools and releases it's humidity very often.

    I can also see it being psychological very easily. All day long we are exposed to massive amounts of blue light, scattered in the sky. By contrast, reds look redder. Overnight, we are exposed to more pure white light, or no light at all. The sunrise is not affected by biased perceptions, so does not look disproprtionately red.

    Then again, I ain't seen a sunset in years. I just like theorizing.

    Njorl
     
  13. Jul 24, 2004 #12

    Monique

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    A red sun is related to bad weather, I think it has to do with the humidity of the atmosphere.
     
  14. Jul 24, 2004 #13
    "Red sun at night, sailors delight; red sun at dawn, sailors take warn." Or something like that.
     
  15. Jul 24, 2004 #14

    Ivan Seeking

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    Hmmm I just noticed this. I should have said held at the indicated temperature.
     
  16. Jul 24, 2004 #15

    Ivan Seeking

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    Why no sunsets? Weekends?

    I don't know if this would apply or not. It only takes a few minutes for our eyes to adjust even to extreme changes in the light's intensity. There is an interesting eye exercise in which one closes the eyes tightly and then directs the line of sight at the sun. Slowly move the eyes back and forth as if scanning the horizonbut move the eyes as far as possible in each direction. Do this three or four times. Now, look away from the sun and open the eyes. This is designed to saturate the vision system with various chemicals that heighten sensitivity to color...I think. I'm no expert on this I have just read about it and tried it a few times. Anyway, everything will appear brighter, and a little yellow, but this fades after just a minute or two.
     
    Last edited: Jul 24, 2004
  17. Jul 24, 2004 #16

    Monique

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    This is what I found :smile::
     
  18. Jul 24, 2004 #17

    Ivan Seeking

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    With Njorl's comments in mind, does anyone know if we perceive light differently if we are tired; such as having greater sensitivity to reds rather than blues due to a loss of some chemical in the brain...for example? Might we have different chemical levels in the morning, as opposed to the evening hours when we might be very tired...or even when hot? Now that I think about it, it seems that when I am extremely hot I may precieve color slightly differently. I am reaching here but this seems to ring a bell of some sort...
     
  19. Jul 25, 2004 #18
    temperature

    Beautiful red evening sunsets after the fall equinox start to appear and fade out, here with the spring equinox, or so. Thats not to say you might not have them all year in other areas. But we do not have blues skys here in summertime much, because of high evaporaton of sea water if you are on the coast, so we would have no red sunsets. If you go inland 80 K to 3,000mt, you can see a red sunset anytime looking south to the Mediterranean Sea, with the same angle of view but we do not. Morning sunrises are always bright and red yellow here at that same time period. The difference is in the evening the reds in ths sky, are as if Picasso used a paint brush. In the morning it is an intense hew of red yellow equally scattered. There is always about the same humidity and no pollution here. From just simple observational experience, it appears that the reds in the sunset or sunrise seem to be related to temperature differnces, that are related to the dynamics of the composition of our atmosphere. But also the point of the observer and air molecule composition would change the tone of the red. Remember when Gary Indiana had black red sunsets when the steel mill production was at its height... It would be nice to know what the relation there is between eyesite, atmosphere and dynamics of particles, to why we have red suntsets, on a lower limit explanation.
     
  20. Aug 7, 2004 #19
    close
    It is red sky in the morning sailors take warning.
    Red sky at night sailors delight.

    Weather (fronts) have clouds. The prevailing wind is from the west. The sun rises in the east, sets in the west. If the weather hasn't arrived yet you get red only in the morning because when the sun is setting it has clouds from the front interfering. Conversley red at night when the front is east of you.
     
  21. Aug 8, 2004 #20
    photons and sky color

    It was suggested on another thread that photon energy levels in different parts of the sky was the reason why we see color differently in different areas of the sky at different times.

    Could this be a very close to the last Why, the sky is the color it is, on the most fundamental level of the micro because of photon energy levels, in different parts of the sky? Photons do carry the color frequency to our eye pupils to register, the color seen.

    Can anyone give me some insight who understands this clearly?
     
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