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Kas ir zaļais stars???(fizikā)
Jau iepriekš paldies par atbildi:)
28, 2006, 22:32Inese
:-:

    Izskaidrot zaļo staru var ar fizikas, precīzāk, optikas zināšanām, bet pati parādība ar tādu romantisku pieskaņu. Zaļo staru var novērot reti un jāskatās uzmanīgi. Zaļais stars veidojas saulei rietot un redzams tad, kad pati saule jau ir aiz apvāršņa, tik, pateicoties gaismas laušanai atmosfērā, saules „zaļā daļa” vēl nav „norietējusi”. Tagad mukšu, kamēr fiziķi par šādu skaidrojumu nav vēl mani iekaustījuši =)
    31, 2006, 10:02Zirneklītis

    C.09 What is the Green Flash (or Green Ray)?
    --------------------------------------------------------------------------------
    Geoffrey A. Landis <geoffrey.landis@lerc.nasa.gov >
    When the sun sets, sometimes the last bit of light from the disk itself
    is an emerald green. The same is true of the first bit of light from
    the rising sun. This phenomenon is known as the "green flash" or "green
    ray." It is not an optical illusion.
    The green flash is common and will be visible any time the sun is
    rises or sets on a *clear*, *unobstructed*, and *low* horizon. From
    our observatory at Mt. Hopkins, I (SW) see the sunset green flash
    probably 90% of the evenings that have no visible clouds on the
    western horizon. It typically lasts one or two seconds (by estimate,
    not stopwatch) but on rare occasions much longer (5 seconds??). I've
    seen the dawn green flash only once, but a) I'm seldom outside
    looking, b) the topography is much less favorable, and c) it takes
    luck to be looking in exactly the right place. If you'd like to see
    the green flash, the higher you can go, the better (see below).
    The explanation for the green flash involves refraction, scattering,
    and absorption. First, the most important of these processes,
    refraction: light is bent in the atmosphere with the net effect that
    the visible image of the sun at the horizon appears roughly a solar
    diameter *above* the geometric position of the sun. This refraction
    is mildly wavelength dependent with blue light being refracted the
    most. Thus if refraction were the only effect, the red image of the
    sun would be lowest in the sky, followed by yellow, green, and blue
    highest. If I've understood the refraction table properly, the
    difference between red and blue (at the horizon) is about 1/40 of a
    solar diameter.
    Now scattering: the blue light is Rayleigh scattered away (not Compton
    or Thomson scattering).
    Now absorption: air has a very weak absorption band in the yellow.
    When the sun is overhead, this absorption hardly matters, but near the
    horizon, the light travels through something like 38 "air masses," so
    even a weak absorption becomes significant.
    The explanation for the green flash is thus, 1) refraction separates
    the solar images by color; 2) at just the right instant, the red image
    has set, 3) the yellow image is absorbed; and 4) the blue image is
    scattered away. We are left with the upper limb of the green image.
    Because the green flash is primarily a refraction effect, it lasts
    longer and is easier to see from a mountain top than from sea level.
    The amount of refraction is proportional to the path length through
    the atmosphere times the density gradient (in a linear approximation
    for the atmosphere's index of refraction). This product will scale
    like 1+(h/a)^(0.5), where h is your height and a the scale height of
    the atmosphere. The density scale height averaged over the bottom
    10 km of the atmosphere is about 9.2 km, so for a 2 km mountain the
    increase in refraction is about a factor 1.5; a 3 km mountain gives
    1.6 and a 4.2 km mountain (e.g., Mauna Kea) gives 1.7.
    More details can be found in _The Green Flash and Other Low Sun
    Phenomena_, by D. J. K. O'Connell and the classic _Light and Color in
    the Open Air_. A refraction table appears in _Astrophysical
    Quantities_, by C. W. Allen. There's also an on-line resource at
    <URL:http://mintaka.sdsu.edu/GF >.
    20, 2007, 2:16zaarciniex
    atvainojiet par anglju val.
[Your answers and comments can be added here]

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