I followed the New Horizons Mission a little, and saw among others this image of Pluto:

Pluto's eclipse

I wonder, why you can't see any stars on it. As far as my very basic knowledge in astronomy goes, I think you can even see stars during a "Sun-Moon-Eclipse" here on earth. So besides having here a spectacular "Sun-Pluto-Eclipse", I further more ask myself if that eclipse is even necessary to see other stars, as those pictures are already taken quit far away from sun, and outside an atmosphere.

Is that not enough to see stars? Or does NASA remove the stars from the images, before publishing them? (If so, why? Not to distract?)

Thanks for answers!

  • 5
    $\begingroup$ Nasa doesn't remove them. Google the question "Why can't we photograph stars" and you'll get some discussion on this subject. What our eyes see and what a camera captures aren't the same. If we were in a space ship when that photo was taken, we'd see stars from the ship's window. That photo probably was taken from some distance at a narrow angle too. $\endgroup$
    – userLTK
    Commented Jul 28, 2015 at 12:00
  • $\begingroup$ Just as a note, we can see stars during a total eclipse. Pictured above is analogous to an annular eclipse. $\endgroup$
    – user21
    Commented Jul 28, 2015 at 15:06
  • $\begingroup$ Telescope Aperture: 75 mm Focal Length: 657.5 mm But they do funny things with the CCD array: Single pixel Field of View: 19.77 μ rad x 19.77 μ rad TDI array FOV: 5.7 ° x0.037 ° More: boulder.swri.edu/pkb/ssr/ssr-ralph.pdf I've no idea what sort of exposures they used for the above shot. $\endgroup$ Commented Jul 28, 2015 at 16:37
  • $\begingroup$ Here's an article on a similar subject: skywise711.com/Skeptic/MoonPics/MoonPics.html $\endgroup$
    – userLTK
    Commented Jul 29, 2015 at 3:56
  • $\begingroup$ Focal length of 657.5mm is very narrow? With Pluto dominating much of the view it wouldn't be surprised if a bright or local star simply wasn't in the view. However, as the Sun is not overexposed, it is probably safe to assume that the exposure would not have captured another star were one in the field of view anyway. $\endgroup$ Commented Jul 29, 2015 at 10:02

2 Answers 2


The answer by @mso is very good. Another contributing factor is the exposure time of the camera on New Horizons.

The amount of light reflecting from Pluto is greater than that from the background stars. As a result the exposure time is set to achieve a good image for the desired target and detail required.

Over the integration time the amount of light from background stars is not enough to register onto the focal plane and subsequent image.

In order to get good pictures of stars one needs to integrate over long period of time while maintaining accurate pointing.


This picture was taken when the probe was 2 million km further away from Pluto (http://www.slate.com/blogs/bad_astronomy/2015/07/24/pluto_ice_flows_and_a_ring_of_light.html). At that distance the angular size of Pluto would be only 4'5". The picture itself must be a zoomed up image. It is quite possible that there was no bright star present in and around this small angle. The unzoomed image could be like following manually created graphic:

enter image description here

It is remarkable how a spacecraft so far away was guided to come on that line passing through Sun & Pluto with camera properly aligned to take this great picture.


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