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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You have two different claimes
> **solar system 50 million light years away**
>
> galaxy 50 million light years away
Do you have link to an image of 50 million light-years away?
You can take image of galaxies far away because they are enormous
Look at the [Andromeda galaxy](https://apod.nasa.gov/apod/image/0612/m31abtpmoon.jpg)[ and the moon to scale](https://apod.nasa.gov/apod/image/0612/m31abtpmoon.jpg). The andromeda galaxy huge but faint so you need to collect light for a long time. You can de the bight center with the naked eye but not the rest of the galaxy because it is to dim.
So the reason you can see other galaxies with your naked eye is not the size but because they are to dim.
Here is a galaxy 30-50 million light-years away [NGC_4697](https://en.wikipedia.org/wiki/NGC_4697) The apparent size is 4′.4 × 2′.8 this is 4×2 arcminutes or 240×120 arc seconds
An arcminute (‘) is 1/60 of a degree and an arcsecond (”) i 1/60 arch minute. You can look up the angular diameter of planets in our solar system [here](https://en.wikipedia.org/wiki/Angular_diameter).
After the sun and moon venus has the largest apparent size to us when it is closest. It is 9.7″ – 1′6″ so when closest to use it is 1×1 arcminutes this is 1/8 if th size of the galaxy 30-50 million light-years.
A human eye can resolve between 20-60 arcseconds so we would see a galaxy at millions of light-years larger then a single dot if it was bright enough.
So because galaxies are so huge they can be larger than anything except the moon and the sun in our sky. Galaxies are not small but they are dim so you need a telescope that can collect a lot of light for a long time to spot them. It is not the magnification that it the primary goal for the most telescope but large light collecting capacity.
There are the limit of how small stuff, in angular size, you can see depending on the diameter of the telescope. To see the lunar lander on the moon that is around 4 meters wide you need a telescope with a 100-meter diameter lens. You would need to put it in space so you do not have any atmospheric effect.
The Hubble space telescope with a 2.4-meter mirror can only see stuff that is 200 meters in diameter on the moon.
[https://www.discovermagazine.com/the-sciences/moon-hoax-why-not-use-telescopes-to-look-at-the-landers](https://www.discovermagazine.com/the-sciences/moon-hoax-why-not-use-telescopes-to-look-at-the-landers)
So galasies is huger but faint so you need to collect a lot of light to see them with a large telescope and long observation time.
High magnification require enormous telescopes and you would need to put the in orbit so the atmosphere is not the limiting factor.
Simple: more light is being emitted from the solar system’s star than the rock or any other planet even one light year away. Stars are unfathomably gigantic and have been burning uninterrupted long before mankind ever existed, meaning their light has already had plenty of time to get here in detectable amounts.
Likewise, planets–even if we had powerful enough telescopes–would likely have an atmosphere of some kind, which means there’d be no possible way of looking directly at the surface via conventional means.
a) the star is actively sending out light, it is shining while the surface of a planet only reflects a tiny bit of light back out
b) the star is several million times larger than a rock on a planet, so even if the planet is something “close” like one in Alpha Centauri, the size/distance ratio still favors the star.
c) planets have atmospheres. hard to see through clouds from above (which is part of the reason we send those rovers to mars, to land there and take pics from there)
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.
We absolutely cannot take photos of solar systems millions of light years away. The most distant planet ever directly imaged is 1200 light years away. The rest are a few dozen light years away. We don’t detect planets by taking pictures of them, we detect them by looking at their effects on their host stars.
As for distant galaxies, they’re huge (thousands of light years across) and insanely bright (containing trillions of starts) whereas a rock is tiny and emits no light of its own.
Arcsecs of a Milky Way-sized galaxy 50 million lightyears away:
D = θ d / 206,265 –> θ = (D*206,265)/d)
Where D = size of galaxy, θ arcsecs, and d = distance to galaxy
100000 LY = (θ * 50000000 LY)/206265 => **θ = 412.53 arcsecs**
Arcsecs of coin-sized rock on the Moon:
0.00001 km = (θ * 384400 km)/206265 => **θ = 0.0000054 arcsecs**
So, the galaxy you’re talking about is about 70 million times larger than the small rock on the moon, from the PoV of Earth. To add to that, the galaxy is also much brighter.
Now, let’s look at what would be the smallest object the Hubble Telescope (with a resolution of 0.04 arcsecs) would be able to see on the Moon:
D = (0.04 * 384400 km)/206265 => **D = 74.5 m**
This means that a squareish or roundish object that is 75 m across would, if places perfectly, take up one pixel on a perfect Hubble Telescope image. And if that object was a rock on the moon, that pixel would be roughly the same color as all the pixels around it. This resolution can be increased a bit by taking multiple images with a very slight change in in the Hubble Telescope’s direction and then algorithmically stitching these images together.
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).
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