I recently saw a photo somebody posted of a galaxy 50 million light years away. I have always wondered, why doesn’t he point it at the moon or even a planet 10 light years away and see the surface up close? We might see water or certain organisms. I have yet to see a picture like that in my lifetime. Thanks in advance for the answer.
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We can’t see solar systems that far away. For the most part, we can’t even see individual stars. We can see galaxies because they are very large, very bright, and stand still nicely for ultra-long exposures.
The same degree of magnification that displays distant galaxies shows things on the scale of mountains on other planets and the scale of parking lots on the moon.
Same reason you can see a camp fire many miles away at night but can’t see the detail of an ant’s foot a few feet away from you even in daylight.
is about what can be resolved with the imaging technology
>**Hubble’s** 94.5-inch mirror has a resolution of 0.024″ in ultraviolet light, which translates to 141 feet (43 meters) at the **Moon’s** distance. In visible light, it’s 0.05″, or closer to 300 feet.
so objects smaller than 300′ across are simply too small to be resolved, they would be smaller than a single pixel in an image generated by the hubble
The galaxy might be a trillion times further away than the coin, but it’s a trillion trillion times bigger.^1
As an example, as seen from the Earth, the Andromeda galaxy is something like six times the diameter of the moon. If it were bright enough to be naked-eye visible, it would be astounding.
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^1 I just looked it up. The actual numbers are 7 × 10^14 times further and up to 2 × 10^23 bigger.
For the same reason that you can see a mountain from hundreds of miles away, but can’t read a newspaper when it’s on the opposite side of the room from you. Because the mountain (and that galaxy) is much, much larger than the newspaper (or rock).
> see the surface up close. We might see water [droplets] or certain [microscopic] organisms.
A telescope is not a microscope. The microscope works by taking a very bright point of light and **magnifying** it. The telescope works by taking vast amounts of spread out light (diffuse light) and **focusing** it. Telescopes are not binoculars or magnifying glasses either. Binoculars work by taking a small amount of straight focused light (not diffuse) and magnifying it.
If you point the telescope to a nearby object, say the moon, it will take in vast amounts of light of equal luminosity and focus it all down to a uniform pixel. You won’t see any fine detail, certainly not any organisms or water droplets.
Here’s a relevant passage from an article on the Hubble telescope about its optical limitations.
>Hubble’s 94.5-inch mirror has a resolution of 0.024″ in ultraviolet light, which translates to 141 feet (43 meters) at the Moon’s distance. In visible light, it’s 0.05″, or closer to 300 feet. Given that the largest piece of equipment left on the Moon after each mission was the 17.9-foot-high by 14-foot-wide Lunar Module, you can see the problem.
The galaxy 50 million light years away is proportionally wayyyyy bigger than the coin on the moon
A coin on the moon is trying to see a 2 cm wide object at 400,000 km. Lets scale that up a bit and its equivalent to trying to see something 473 kilometers wide at 1 lightyear, or 23,650 kilometers wide at 50 light years.
Seeing a star that’s a few million km in diameter at 50 light years is closer to seeing a good sized rock (1.2 meters) on the moon than a coin, and generally we’re looking at galaxies which are thousands to millions of lightyears across so its more equivalent to just seeing the moon at all.
The answer lies in the resolution of the images taken by the telescope which are blounded by the laws of physics. The resolution is the smallest picture element aka pixel. More the number of pixels better the clarity of an image.
But in case of telescopes, larger mirror results in better magnification of an object. But the magnification is also affected by the wavelength of light.
Shorter wavelength like UV light produces fine detailed image than longer wavelength visible light.
Let’s take an example of Hubble telescope which has a mirror diameter of 2.4 metres. It produces a single pixel resolution in UV light of 43 metres spread across moon’s surface. So, anything smaller than 43m will be hidden under a single dot which cannot be magnified further.
To study anything on a surface of moon we need 2 pixels or more.
Unfortunately we don’t have a telescope powerful enough yet to directly image a planet in another solar system with any detail. But there’s some we can image as simple smudges of light. Here’s a list in Wikipedia: [https://en.wikipedia.org/wiki/List_of_directly_imaged_exoplanets](https://en.wikipedia.org/wiki/List_of_directly_imaged_exoplanets)
Planets are absolutely tiny. They are like motes of dust floating in space relative to other astronomical objects we can see. I don’t think we’ll be looking up close at extrasolar planet surfaces with a telescope for some time. For perspective here’s maybe the best image we have of the surface of another star: [https://phys.org/news/2018-01-astronomers-images-surface-giant-star.html](https://phys.org/news/2018-01-astronomers-images-surface-giant-star.html)
That star is 350 times the diameter of the sun and you can see how little detail there is in the image.
We do point telescopes at the moon though and those images are very detailed. There’s plenty if you search for them. Even a simple pair of binoculars can make out impressive detail on the moon. Of course the moon is only 300,000km away.
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