The Moon symbolizes time and Lord Shiva wearing the moon on his head denotes that Shiva has complete control over time and is beyond the measure of time and is eternal.

Shiva Tattva is where there is no mind and the moon signifies the mind. When there is no mind then how can this ‘no mindedness’ be expressed and how can anybody understand it? You need a little bit of the mind to understand, experience and to express.
The no-mind, infinite consciousness requires that little bit of mind to express itself in the manifest world. So, to express that inexpressible, that little mind (crescent moon) is on the head.
Wisdom is beyond the mind, but it needs to be expressed with a tinge of mind and this is symbolized by the crescent moon.

From a scientific and philosophical point of view, the moon on Shiva’s forehead depicts control on time in terms of nature. The waxing and waning of the moon was used to calculate the days and months in earlier times.

Thus, the Moon symbolizes time and Lord Shiva wearing the moon on his head denotes that Shiva has complete control over time and is beyond the measure of time and is eternal. Control on time and the moon is important to control nature. An example that can quote here is the high tides and the low tides that arise due to the gravity of the moon. Hence, it is Chandrashekhara alone who can control time.