When space probes like New Horizon's are traveling towards their target & they take photographs of their target en-route, does the incoming light need to be adjusted for the Doppler effect because of the speed of the probe?

  • $\begingroup$ New Horizons travels at 16.26 km/s. the speed of light is 299792.46 km/s. I highly doubt that this would be an issue $\endgroup$ – neelsg Jul 10 '15 at 7:27
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    $\begingroup$ @neelsg yeah, but it is the wavelength that is relevant. Indigo light starts at 380 nm, blue at 435 nm. Shift wavelength by 1 nm/s, that could be significant, if you are trying to use color to deduce composition. $\endgroup$ – kim holder Jul 10 '15 at 14:52
  • $\begingroup$ Isn't this concept the basis of redshift? As long as the subject you're trying to photograph is illuminated with black body radiation with a known shift (or is emitting it), you should be able to determine how shifted the light is and compensate. Note: I say this as a layperson, so take it with a grain of salt..... $\endgroup$ – bmhkim Jul 10 '15 at 16:51
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    $\begingroup$ You can also use spectroscopy to detect redshift. Each molecule gives a known series of absorption lines. If that series is offset, you can work out the red/blueshift factor/speed. $\endgroup$ – Hobbes Jul 10 '15 at 19:17

You can calculate the wavelength shift between the transmitted light and that observed by the receiver from the doppler equation:

$$\lambda_r = \frac{\lambda c}{(c - v_r)}$$

The Helios probes reached a speed of $70km/s$ as they approached the sun. What effect would that have on them observing something with a wavelength of $600nm$?

$$\lambda_r = \frac{(600nm)(3.0\times 10^8 m/s)}{(3.0\times 10^8 m/s) - (7.0\times 10^4 m/s)}$$ $$\lambda_r = 600.14nm$$

It's unlikely that any sort of external sensor observations are going to be affected by shifts of that magnitude. However communications (which rely on very precise timing) can be affected. This was potentially a problem with the Huygens-Cassini mission


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