2
$\begingroup$

I constructed a telescope and fixed my mobile's camera to the eye lens. I then viewed the sky via the mobile and I captured this image.

enter image description here

This is the magnified version of it:

Magnified

I'm not sure if this actually the spectrum of a star because I feel like maybe the human oil secreted by my hands may have got stuck on the lens and that must've dispersed the light from some source. I'd like to know all of your views. Thanks.

$\endgroup$
  • 1
    $\begingroup$ I think it is a real spectrum, created by chromatic aberration (see this answer). Can you describe a little more about the telescope itself? Was it a refractor for example? $\endgroup$ – uhoh Feb 24 '18 at 2:37
3
$\begingroup$

The other answer (since deleted) is not right. The blob is a dozen pixels long, but monotonic in color change. It has nothing to do with the Bayer filter.

It's almost certainly chromatic aberration from some combination of the telescope and eyepiece optics and the camera optics. The short focal length and therefore tiny entrance pupil size of a cell phone's camera only intercepts a small fraction of the bundle of rays from the eyepiece's exit pupil meant to fill a human pupil. If it were offset from the center, it would sample rays near the edge of the path, subjected most strongly to chromatic aberration. So even if the star appeared in the middle of the recorded image, this offset could result in a first-order dispersion.

If you look at the three color "blobs" (caused by the shape of the transmission spectra of the three color filter types) the RED and GREEN blobs overlap, but the blue blob is offset much farther from the other two.

This is consistent with the dispersion characteristics of glasses and plastic, where the index of refraction changes more and more rapidly toward the blue end of the spectrum, as the energy of the photons get closer to a real absorption edge somewhere in the UV.

enter image description here

enter image description here

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.