Eli5: Why can we see galaxies but not closer stars/planets


The JWST took a picture of a cheek load of galaxies, yet we can’t see pluto very well? The answer is probably super simple lol

In: 12

Average diameter of a galaxy: 100,000 light years, which is about 950,000,000,000,000,000 kilometers. They’re also made up of billions or even trillions of stars, all of them producing light.

Diameter of Pluto: 2376 km. It’s a chunk of rock in space which only reflects light and doesn’t create its own.

Edit: forgot a word.

The only way we see anything in space is with radiation of some sort. Usually light, as that is the easiest radiation to produce.

Things that make radiation, so stars and huge explosions, are easy to spot. It glows. Things that don’t, like planets, are incredibly small black dots on a black background.

They’re much bigger and brighter, assuming you live near one, you can see a mountain 100 miles away but I doubt you’d spot a the bee that’s 100 feet away

It’s just like in a night you can easily see things that shine themselves, but to see other things you need something to shine light on them and illuminate them. As pluto is very small and very far away, then only a small fraction of the Suns light shines on it, making it very, very dim.

It’s like in a night with flashlight, you can only see so far, as father objects are the more dim they are, and at some distance they are essential as black as parts that are not lit by flashlight. But your flashlight can be seen from much greater distance.

Galaxies are very, very big relative to planets.

The Andromeda Galaxy – the closest large galaxy to Earth besides our own Milky Way – would be several times the size of the Moon in the sky if it were bright enough for us to see all of it with the naked eye. Pluto, on the other hand, is smaller in the sky than a person a few hundred miles away would be.

That said, we *can* see Pluto in Hubble, much less in the JWST. Just not in very high resolution.