in Thoreau’s Journal:

In proportion as I have celestial thoughts is the necessity for me to be out and behold the western sky before sunset these winter days.

That is the symbol of the unclouded mind that knows neither winter nor summer. What is your thought like? That is the hue, that the purity and transparency and distance from earthly taint of my inmost mind; for whatever we see without is a symbol of something within, and that which is farthest off is the symbol of what is deepest within. The lover of contemplation, accordingly, will gaze much into the sky. Fair thoughts and a serene mind make fair days.