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NASA published this wonderfull video of Sun from SDO:
https://www.youtube.com/watch?v=GSVv40M2aks

And it occurred interesting question: Sun is very big sphere. Its so big that it took light 4,6 seconds to traverse distance of diameter of the Sun. Every point on Sun surface emits photons. So when we make directly photo of the Sun then different pixels will contains record of light emited in different times.

Have it some sense to care about (de)synchronicity of pixels in images of the Sun? How big will be difference between photos of the sun if time correction for pixels will be applied to sync them?

Illustrative image:
Pixel A in photo of the sun contains record about color of surface point in time t and pixel B in time (t - 2.3s)

Pixel <code>A</code> in photo of the sun contains record about color of surface point in time <code>t</code> and pixel <code>B</code> in time <code>(t - 2.3s)</code>

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  • $\begingroup$ Interesting idea and not a hard imaging problem. Needs a name - "projected real-time imaging" perhaps?. What is the frame rate? $\endgroup$ Feb 16 '15 at 22:14
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A dirty little secret of remote sensing: This image of the Pribilof Islands taken by Landsat 8 taken on September 22, 2014 is not time-synchronized.

Landsat, along with many remote sensing vehicles in low Earth orbit, build their imagery one pixel at a time, with each pixel taken at a slightly different time. The appearance of an image is a consequence of rotating mirrors or back-and-forth scanners, coupled with the satellite's motion. (Some satellites with a more modern design scan a line at a time.)


This image taken by GOES-13 at 1431 UTC on January 27, 2011 also is not time-synchronized:

The GOES satellites, being geostationary, cannot take advantage of their motion with respect to the Earth to build up an image over time. Instead, the GOES satellite scanners step across horizontally to construct one line of the image, then step vertically, then step horizontally to construct another line of the image. It takes a few minutes to construct a full image.


That these images are not perfectly time synchronized is pretty much irrelevant. The relatively tiny time discrepancies between various parts of an image from a CCD-based imager such as SDO are even less important.

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  • $\begingroup$ So what you are saying is that Sun is quite static on timescale of seconds, right? $\endgroup$
    – Ruslan
    Feb 17 '15 at 6:20
  • $\begingroup$ @Ruslan - Exactly. $\endgroup$ Feb 17 '15 at 8:00

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