Do Objects Always Appear Smaller with Distance? Not on Cosmic Scales!

"If you're on the surface of Earthand I'm betting you arethere are many ways to reliably estimate the distance to some object. One we use almost subconsciously is to compare an object's apparent size with how big we know it to be. For example, you have a good feel for the size of, say, a typical human. So if you see someone looming large in your vision, you can reckon they're nearby, whereas if they appear very small, they must be much farther away."

"And the overall trend is crystal clear: the farther off an object is, the smaller it appears. The trend is so obvious, in fact, that we can see the rate of change is linear: Double the distance, and the object will appear to be half its previous size. Look at it 10 times farther away, and it will seem to be one tenth as big."

Human perception estimates distance by comparing an object's apparent size with its known physical size, producing an inverse linear relation: doubling distance halves apparent size. This method works for familiar objects across terrestrial scales and up to a few kilometers. Astronomers require distances to objects separated by trillions of kilometers or billions of times farther, including galaxies ranging from tens of millions to billions of light-years away. Galaxies have wide intrinsic size variation, so their apparent sizes in deep telescope images do not monotonically indicate distance. Therefore apparent angular size alone cannot reliably determine a galaxy's distance.

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