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I Colour star versus temperature

  1. Jun 17, 2017 #1
    Hello I am interested about correlation between star surface temperature and its visioned colour ,for example orange red Arctur has surf temperature cca 4300 K ..but comparing to for example hot piece of metal? its temperature 2000 K respond white colour. ? What is a matter of this disagreemet?
    Thank you very much. best regards T.Bruha
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  3. Jun 17, 2017 #2


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    hi there
    welcome to PF :smile:

    you have labelled you thread with the intermediate tag indicating a higher education
    what research have you done so far to answer this question ?

    ohhh btw ... this should have been in the astronomy forum .... I will ask for it to be moved

  4. Jun 17, 2017 #3


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    There is a wide range of surface temperatures that produce a light that can be called "white" and the difference between them can often only be spotted when they are compared side by side. This wiki link shows how the Colour of a hot object relates to its temperature. The picture is only illustrative, of course but shows how Arctur (at 4300K) looks orange, relative to a hotter star at say, 6000K. See Planck's Law. The spectral curves for a black body will peak at different wavelengths, depending on the temperature (Google Colour Temperature) A very hot piece of metal can look white, when it's only a bit hotter than 'Red Hot'; that's a subjective thing.
  5. Jun 17, 2017 #4
    Thank you very much for answer ,I will check links.
    Best regards T.Bruh
  6. Jun 17, 2017 #5

    Vanadium 50

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    Visible (perceived) color depends on intensity as well as frequency, so you won't be able to put temperature and color in 1:1 correspondence.
  7. Jun 17, 2017 #6
    Hello thanks for answer
    (I though something as this. I was hyphothesised if there could not be redshift effect but probably not...) hi T.Bruha
  8. Jun 18, 2017 #7


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    I have a feeling that you are referring to appearance with the unaided eye(?).
    Red shift is very slight and undetectable by the eye for sources that are actually visible unaided. I think that sources which display significant red shift would be too faint to see with optical viewing, even with a large telescope) and astrophotography would be needed to detect them - and measure the red shift.
  9. Jun 18, 2017 #8

    stefan r

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    Molten iron:

    ?u=http%3A%2F%2Frapidfreak15.files.wordpress.com%2F2013%2F02%2Fmolten-iron.jpg 220px-Melted_raw-iron.jpg
    Optical image of the star Arcturus:

    Speaking of "white hot iron" and "red giant stars" makes sense when you compare them with similar objects. For instance a red hot iron and a blue star like Rigel:

    stock-photo-brushed-steel-pot-on-red-hot-electric-stove-59996290.jpg 260px-Treasures3.jpg
  10. Jun 19, 2017 #9
    Thank you very much for answer. so I understandt, that it is relative ,probably depends, on perceived intesity of radiation ( and therefore distance as well ).
    Can I have still one question concerning gravitational redshift unit-beacouse in lot of articel I find as used unit m/s: so it is correct that redshift (%)= redshift (m/s)/300*10exp4? - derivating from light seconde distance?
    thank you and best regards, Tomas Bruha
  11. Jun 20, 2017 #10

    stefan r

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    Can you link the article?
    For a doppler redshift
    z = v/c
    v is the velocity, c is speed of light 3.00 x 108m/s. z is (observed-emitted)/emitted wavelength. 100z is "percent redshift".

    Most astronomy measurements of gravitational redshift will be from much more than 1 light second. We measure from earth and stars are many light years away. Am I miss reading that?
  12. Feb 9, 2019 #11
    Hi this is just for fun…(this period is in Prag only observable planet Mars :H:H:H

    Have nice time

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