Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Can the sun be blueshifted due to Earth's rotation?

  1. Dec 6, 2009 #1
    I used my telescope and a Solar filter to take a shot of the sun and on the bottom half of the circle (due to the mirrors inverting the image) there is a blue outline and on the other side is a red outline. Is this a display of the dopplar effect or just a coincidince?
     
  2. jcsd
  3. Dec 6, 2009 #2

    mgb_phys

    User Avatar
    Science Advisor
    Homework Helper

    It's chromatic aberation in your telescope (that's an optical fault in simple telescopes where the lenses can't focus all the colours equally well)

    The doppler effect wouldn't have much effect on the light from a black body since any visible light that was red-shifted would be replaced by UV light that had been redshifted into the visible
     
    Last edited: Dec 6, 2009
  4. Dec 6, 2009 #3

    Matterwave

    User Avatar
    Science Advisor
    Gold Member

    I doubt it's a dopplar effect since to red/blue shift the Sun's primarily Yellow/green light to a degree that you notice the light as red/blue the velocities required would be immense (a good fraction of the speed of light).

    By my calculations, it's somewhere around 10 percent the speed of light, or 30,000km/s

    By comparison, the speed of the galaxy's rotation (basically as fast as it gets) is only around 220km/s for our Sun's local vicinity.
     
  5. Dec 6, 2009 #4

    russ_watters

    User Avatar

    Staff: Mentor

    None of the above. It's refraction due to the earth's atmosphere bending different wavelengths of light by different amounts. The lower an object is to the horizon, the worse it gets. It's ok, though, many astronomical image editing programs have features to align the different color channels. I use Registax, which is a stacking program, but you can also do it manually with Photoshop.

    Here's a very good example of it: http://cseligman.com/text/sky/atmosphericdispersion.htm
     
    Last edited: Dec 6, 2009
  6. Dec 6, 2009 #5

    ideasrule

    User Avatar
    Homework Helper

    I'm pretty sure the OP is talking about chromatic aberration. It's very common and much more prominent than the effect russ mentions, which is only apparent near the horizon.

    As an example, here's what I think the OP is talking about: http://23.media.tumblr.com/W9dg7rWdzgf45msuaH6xMS7ko1_500.jpg [Broken]
     
    Last edited by a moderator: May 4, 2017
  7. Dec 6, 2009 #6

    russ_watters

    User Avatar

    Staff: Mentor

    I'm pretty sure it's not. With chromatic aberration, you have a ring around the entire object because one color will be focused while another won't be. With the effect in the OP, the colors are just misaligned.

    Read the link I posted.

    Yes, that's what the OP is describing and it isn't chromatic aberration. It is very noticeably dependent on the altitude of the object above the horizon.

    Here's another refrence, this one in Sky and Telescope, also referencing the function in Registax that is specifically designed to fix this issue:
    http://www.skyandtelescope.com/howt...w_to_Process_Planetary_Images.html?page=2&c=y

    Here's an example of chromatic aberration, which is a blue halo around the entire object (note: at the edge of the frame, they can be misfocused and misaligned): http://www.astropix.com/HTML/I_ASTROP/EQ_TESTS/C70_200.HTM
     
    Last edited by a moderator: May 4, 2017
  8. Dec 7, 2009 #7

    Chronos

    User Avatar
    Science Advisor
    Gold Member

    Theoretically there is a slight blue shift on the incoming side [and redshift on the outgoing side]. Too slight to be measurable. Is that an issue?
     
    Last edited: Dec 7, 2009
  9. Dec 7, 2009 #8

    Matterwave

    User Avatar
    Science Advisor
    Gold Member

    You'd never be able to see that shift. You need some advanced detectors to do it since the shift is at most a fraction of a nanometer in the wavelength.
     
  10. Dec 7, 2009 #9
    Agreed.
     
  11. Dec 7, 2009 #10

    chemisttree

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    I'm with Russ on this one. How likely is it that the poster took a pic of the sun at zenith? Nil.
     
  12. Dec 7, 2009 #11

    Redbelly98

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    It doesn't have to be at zenith, just well away from the horizon.

    If the sun was off-center in the field of view, chromatic aberration won't be uniform around the circumference.

    ca-bird.jpg

    https://www.galileoscope.org/gs/sites/galileoscope.org.gs/files/Chromatic-Aberration.jpg [Broken]

    Source for moon photo:
    https://www.galileoscope.org/gs/content/specifications
     

    Attached Files:

    Last edited by a moderator: May 4, 2017
  13. Dec 8, 2009 #12

    chemisttree

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Chromatic abberation on a newtonian? First I've heard of that one...

    What is the likelihood the poster was photographing the sun in Dob's hole?
     
  14. Dec 8, 2009 #13

    mgb_phys

    User Avatar
    Science Advisor
    Homework Helper

    Doesn't mean there actually were mirrors in the telescope - have you ever done computer tech support?
    What people say is wrong rarely bears any resemblance when you get there.
     
  15. Dec 8, 2009 #14

    chemisttree

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Yes, there is that I suppose. I'm just reading what the poster typed.
     
  16. Dec 8, 2009 #15

    Redbelly98

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    A cheap camera lens could produce chromatic aberration. The optical system is not 100% mirrors.
     
  17. Dec 8, 2009 #16

    chemisttree

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    So, you think it was a cheap camera that caused it?
     
  18. Dec 8, 2009 #17

    Redbelly98

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    I'm saying the possibility is not ruled out. All the information we have is contained in post #1. There is no image posted, no mention of the camera or telescope type (except that the telescope has mirrors). We don't know if the sun was near zenith, near the horizon, or somewhere in between. We don't know the position of the sun within the image.

    There has been no followup by the OP to clarify any of our speculation.
     
  19. Dec 9, 2009 #18

    ideasrule

    User Avatar
    Homework Helper

    I stand corrected; I've always assumed, for some reason, that only chromatic aberration can produce a halo like that. (I should have known this wasn't the case because I often saw such a halo with my Newtonian telescope. I don't remember the effect being dependent on altitude, but that's probably because I wasn't looking for a dispersion vs. altitude relationship.)
     
  20. Dec 9, 2009 #19

    russ_watters

    User Avatar

    Staff: Mentor

    An astronomical camera is no mirrors or lenses - it's just a chip....though I am assuming a real astronomical camera was used. The telescope itself is the entire optics - and even then, it's just the objective and secondary. Ususally, you don't use eyepieces.

    While you are right that the information we have doesn't quite rule out chromatic aberration, it does make chromatic aberration extremely unlikely. The OP said they used a telescope, which makes it very difficult to get an object the size of the sun completely off to one side in an imager.

    I tend to answer these questions based on what is reasonable.
     
  21. Dec 9, 2009 #20

    Redbelly98

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    Well, you do have a lot more experience in the subject than I. I've taken another look at one of my (non-astro) photos that had chromatic aberration, and there is only extraneous purple, no red, in it. Plus, I am kicking myself for forgetting that the primary+secondary mirrors alone, no added lenses, are the preferred way to take a photograph.:redface:
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Can the sun be blueshifted due to Earth's rotation?
  1. The suns rotation (Replies: 3)

  2. Rotation of the Earth (Replies: 5)

  3. Earths Rotation (Replies: 3)

  4. Sun rotates? (Replies: 9)

  5. Earth rotation (Replies: 2)

Loading...