Rotate the single sheet of Polaroid in front of your eye while viewing the sky. The sky will darken when the transmission axis of the Polaroid is perpendicular to the direction along which the skylight is polarized.
Work Step by Step
Scattered light is also polarized. If the sun is, say, low in the east, the sky over you will be polarized north and south. Interestingly, before GPS, this principle was used to navigate during flights over high-latitude regions. Look up "twilight compass" for more on this subject.