D&D 5E How far away can a person make perception checks?

[Morrus]

I can see stars hundreds of light years away.

 

[Quickleaf]

If we assume nice open conditions, good weather, pretty flat, at what range would you allow players to start making perception checks to notice things?

Example: An enemy orc is on the horizon, lets say at what distances would you allow a player to check to see if they see something, and can identify it as an Orc:

DC 30 (almost impossible)
DC 20 (tough but a fair amount of people could see it)
DC 10 (you would have to have diminished senses not to notice)

As a follow up to this, there are a few abilities that give some extraordinary sight ranges. For example, the Eagle Totem Warrior, Eyes of the Eagle magic item, and a wildshaped druid as an eagle. So if you go with the 1 mile as the "extreme distance" noted for the eagle totem specifically, would you use DC 30 to start at the 1 mile marker for these types, or a smaller DC?

In your ideal circumstance it's about 3 miles for very big things (structures and gargantuan creatures).

For finer details, like identifying a humanoid by species/race, well, it's ball of "it depends."

I do recall one night when I was bleary-eyed prepping a session with the PCs at an aarakocra cliffside monastery (some 500-feet elevation) serving as evening lookouts against gargoyles that I ended up on some webpage related to naval sighting distances. There was an equation that had to do with how high off the ground you were, time of day, lumens of the light source (if any) you were looking at, and all these factors, though I never wrote down the website.

I ended up going with a night visibility of 300 feet, or 600 feet for creatures with 60’ darkvision (though only in black and white). While I ruled that the PC with an obscenely high Perception and Eldritch Sight could see out to 1,200 ft. What this meant was that from the moment the high perception PC spotted the gargoyles, the party had 10 rounds (1 minute) before the gargoyles were in melee. Thus informed, I counted down, ok they're at 1,000 feet now...anyone doing anything? OK, now they're at 800 feet, anyone? And now, at 600 feet? And so on. It worked well as a tension building mechanic.