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It makes me wonder if there's a distance so great in the observable universe that light from an object would spread out so much that it couldn't be recognized a

It makes me wonder if there's a distance so great in the observable universe that light from an object would spread out so much that it couldn't be recognized as an object. I'd imagine there are distant stars ejected from galaxies that would render only as single pixel. It seems possible given enough distance that an entire galaxy could render as a single pixel as well, but I wonder if that distance is greater than the observable universe.

PeanutNore 8y ago
What exactly do you mean by "render only as a single pixel"? With a low enough resolution sensor, the sun would render as a single pixel when observed from earth.
- stcredzero 8y ago
  A guy who worked at the undergraduate computer lab when I was in college in the 90's was bemused by all of the print samples and signs by the laser printers, so he made his own: The caption read, "This is Chris rendered in one color at 1 DPI on the Dinotronic," underneath a 7x7 monochrome portrait of himself.
jstanley 8y ago
Whether an object falls on to a sensor as a single pixel depends on the magnification (assuming it's correctly focused). Is there a physical limit on how much magnification is possible?
- kswillister 8y ago
  There's a limit imposed on resolution for earth-based telescopes due to blurring caused by Earth's atmosphere. https://en.wikipedia.org/wiki/Astronomical_seeing#The_full_width_at_half_maximum_(FWHM)_of_the_seeing_disc https://en.wikipedia.org/wiki/Astronomical_seeing#The_full_w...
kswillister 8y ago
when you say "a single pixel" here I believe you mean a very small angular diameter
woodandsteel 8y ago
For a reflecting telescope, how many pixels are received from a given object depends in part on the surface area of the main mirror.
xelxebar 8y ago
There certainly are telescopes that capture images of objects so faint we have to wait long periods of time just to catch a few photons. This is enough to do some interesting astronomy, perhaps surprisingly. If you have a big enough telescope and point it at something long enough, you can almost always resolve it better than just one pixel. There is one hard physical limit though. Due to the expansion of space, there are in fact objects so far away that their light will never reach Earth---one might say that space is expanding them away from us at faster than the speed of light. And because this expansion is actually getting faster all objects are actually accelerating away from us. That means all the time, there are objects that speed up from sub-lightspeed to super-lightspeed as they move away from us. Once they cross that lightspeed barrier, their light can never reach us again. So it's concievable that we might just happen to capture the last photon of some object that will ever reach us. In that sense, then, some objects are indeed so far away that for a brief period of time, any image of them can only hope to be a single pixel, no matter how good your resolution or magnification.
planteen 8y ago
I think part of what you are asking is, "If we can't resolve the disk of a object, how do we know if it is a galaxy or a star?" The answer is that we can tell a lot about a point source based on its spectrum. For example, quasars were first noticed solely by their spectra. The other thing to consider with distant galaxies is that they are moving away from us very quickly. The further away they are, the faster they are receding, and the more red-shifted their spectrum becomes. This is why JWST has different spectral response from Hubble.

PeanutNore 8y ago

What exactly do you mean by "render only as a single pixel"? With a low enough resolution sensor, the sun would render as a single pixel when observed from earth.

stcredzero 8y ago
A guy who worked at the undergraduate computer lab when I was in college in the 90's was bemused by all of the print samples and signs by the laser printers, so he made his own: The caption read, "This is Chris rendered in one color at 1 DPI on the Dinotronic," underneath a 7x7 monochrome portrait of himself.

jstanley 8y ago

Whether an object falls on to a sensor as a single pixel depends on the magnification (assuming it's correctly focused). Is there a physical limit on how much magnification is possible?

kswillister 8y ago
There's a limit imposed on resolution for earth-based telescopes due to blurring caused by Earth's atmosphere. https://en.wikipedia.org/wiki/Astronomical_seeing#The_full_width_at_half_maximum_(FWHM)_of_the_seeing_disc https://en.wikipedia.org/wiki/Astronomical_seeing#The_full_w...

kswillister 8y ago

when you say "a single pixel" here I believe you mean a very small angular diameter

woodandsteel 8y ago

For a reflecting telescope, how many pixels are received from a given object depends in part on the surface area of the main mirror.

xelxebar 8y ago

There certainly are telescopes that capture images of objects so faint we have to wait long periods of time just to catch a few photons. This is enough to do some interesting astronomy, perhaps surprisingly. If you have a big enough telescope and point it at something long enough, you can almost always resolve it better than just one pixel. There is one hard physical limit though. Due to the expansion of space, there are in fact objects so far away that their light will never reach Earth---one might say that space is expanding them away from us at faster than the speed of light. And because this expansion is actually getting faster all objects are actually accelerating away from us. That means all the time, there are objects that speed up from sub-lightspeed to super-lightspeed as they move away from us. Once they cross that lightspeed barrier, their light can never reach us again. So it's concievable that we might just happen to capture the last photon of some object that will ever reach us. In that sense, then, some objects are indeed so far away that for a brief period of time, any image of them can only hope to be a single pixel, no matter how good your resolution or magnification.

planteen 8y ago

I think part of what you are asking is, "If we can't resolve the disk of a object, how do we know if it is a galaxy or a star?" The answer is that we can tell a lot about a point source based on its spectrum. For example, quasars were first noticed solely by their spectra. The other thing to consider with distant galaxies is that they are moving away from us very quickly. The further away they are, the faster they are receding, and the more red-shifted their spectrum becomes. This is why JWST has different spectral response from Hubble.