Picture a tidally locked planet that is also the closest planet to the star (~0,17 AU from a star with a luminosity of ~1,5 times that of the Sun).
The side of the planet that faces the star would surely be a scorched wasteland, not sure about the dark side of the planet though, I've thought of the possibility that the dark side of the planet is host to frozen, icy reliefs, but haven't found info to sustain whether this would be plausible or not.
In any case the frozen side, even if plausible, would have little to no light to reflect since it would always point outwards of the system. This leaves us with nothing but one scorched, half surface to reflect light towards the civilisation observing the stars over at the ringed planet ~1,24 AU away from the star. Now, the rings are low albedo, but still make an impact on the visibility of the night sky (an impact I'm happy to dim considerably if needed).
So the question is: How advanced need the civilisation be in order to notice their warmest planetary neighbour is tidally locked to the star?
Are we talking huge observatories? Very developed telescopes? Simple telescopes? Maybe even bare eye because of some reason that escapes my understanding of it all?