The Art of War by Sun Tzu

I Laying plans contd...

[Heaven - number two of the five constant factors to be taken into account in one's deliberations, when seeking to determine the conditions obtaining in the field]

7. Heaven signifies night and day, cold and heat, times and seasons.

Notes by Zephyrist:

Night and day considerations are obviously considerations of light. Small groups have the element of surprise in the dark while large groups may have trouble co-coordinating the battle in the dark.

Cold and heat, consider the extremes of desert and snow, even modern armies have difficulty with temperature extremes with equipment and men breaking down.

Times: attacks at dawn are quite popular especially if you are the side attacking out of the sun and if the enemy is sleepy.

Seasons: relates to cold and heat, some countries get so cold in winter you wouldn't want to fight at all while other countries can be wet in summer with major flooding, again best to give that battle a miss.