M: As the title, a spaceship unexpectedly arrives in Earth's orbit. They aren't here to invade or explicitly to uplift (though they have no great objection to doing so). They're primarily around to perform historical research, as they are in fact human-descended time travelers. The following specifications apply to this scenario.
The ship
-Length: 35 km, radius 7 km (hull), 12 km (warp torus)
-Powered by an antimatter reactor with fuel produced using an onboard Non-Orientable Wormhole; maximum output of 100 Exawatts for FTL
-Is armed with (1) Ultra-Relativistic Electron Beam with a pulse rate of 600 kHz and a beam power output of 60 TW. This weapon is mounted in a turret. They also have an ultraviolet laser with the same output and pulse frequency mounted in a second turret.
-The warp drive in sub-light mode can instantly bring the ship to any arbitrary travel speed along its forwards/backwards axis
-Is fully capable of manufacturing anything in the time travelers' tech base (except wormholes due to massive energy demands)
-Population of several million
The time travel
-Time travel is the result of creative mis-use of the ship's warp drive. It has a hard cap of one year into the past per light year traveled.
-The historians aren't worried about causing paradoxes on account of arriving in the past causing the timeline to fork; they have a communications wormhole connecting them back to their home timeline.
-They're planning on making a stop every decade, going backwards up the timeline; we will be concerning ourselves with their stops in 1980, 1940, 1910, and 1540.
Misc. Notes
-The historians have YES levels of biotech/nanotech/cyberwar, and are heavily transhuman by default. They cannot violate thermodynamics.
-The historians do not want to kill the uptimers unless absolutely necessary
-The historians do not want to be called gods, and will vehemently object to such treatment; they will be fairly open about their actual purpose
So, how do the general populace and leadership of each era respond to the historians arriving? Panic? Attempts at nuclear attack? Unwanted worship? What's your best guess?
Personally, we think Reagan might try to nuke the historians (good luck with that), and the protestant reformation is likely to get... odd.