At one point in "Marvel's Agents of S.H.I.E.L.D.", some agents are on a planet where the day, defined as the length of time where the sun shines on the planet, occurs only once every 18 years for a couple hours.
Is that a plausible scenario? Can the length of the day and the night be drastically different for a given planet?
Please, do not be afraid to be technical in your answer.
EDIT: (After Rob's answer)
On this hypothetical planet, the "conservation of daylight hours" as he called it seems to be violated. In other words, on earth, when you have long days on a specific location in the northern atmosphere, this is compensated by long nights on a corresponding location in the southern atmosphere. On the planet in question, the long nights/short days seem to be the case for all the planet.
Best Answer
It depends what you mean by day and night. The day and night are not of equal lengths now, where I live at latitude 53N. The tilt of the Earth's rotation axis with respect to the ecliptic plane means that this is generally true.
The situation you describe would have to be considerably more extreme. If the planet was in a highly eccentric orbit and had a very large (close to 90 degrees) tilt of its rotation axis with respect to its orbital plane and the tilt was such that one rotation pole pointed "towards" the star and you were talking about the amount of "day" that was experienced by an observed at the opposite pole, then it could be arranged. However note that there is some sort of "conservation of daylight hours" going on here, since an observer at the other rotation pole would experience almost continuous daylight (albeit that in a highly eccentric orbit, the daylight would be very dim for most of the planet's year) with a brief period of darkness.