LittleDan wrote in part:
And facts can be contravercial too. UFO sightings are
called 'facts', but they are, of course, disputed.
They are considered evidence for sentient life on
other planets, but the mainstream considers it false
evidence and therefore defenately a false conclusion.
It's generally uncontroversial that X saw lights in the sky;
occasionally, people suspect that X was drunk or lying,
but even then it's uncontroversial what X /claimed/ to have seen.
What's controversial is that the lights came from a flying object
and if so, whether that object has been correctly identified
as (say) a weather balloon.
And then sometimes, it may be uncontroversial that X saw a flying object
and that nobody has managed to identify the object -- a literal UFO.
Still, the conclusion that the object must be an interstellar spacecraft
is bound to remain controversial.
Whether all this is relevant to a textbook on astronomy
(which typically deals with stars and interstellar gases)
is another matter entirely.
-- Toby