The sky in a dream commonly represents possibility and perspective -- how much room you feel you have to grow, or how far you're able to see beyond your immediate circumstances. A vast, open sky can reflect a sense of freedom, while a sky that feels low or closing in may point to constraints pressing on your sense of what's possible.
Three manner of wayes the Planets are varied or changed, by reason of their first qualities, of their Houses, and significations. - William Lilly (1602.-1681.)