system
Given the following post, respond as if you're commenting on Reddit:
human
Can our brain know what time it is while we're asleep?

Is our biological clock aware of the solar clock?
gpt
Yes! Each cell has a set of specific genes which are transcribed and/or translated rhythmically. For most people, each cycle takes about ~24.3 hours. This coincides with day length and is known as your body's circadian period. As it's slightly longer than 24 hours your body needs to keep re-adjusting to changing day length (if you kept cycling at 24.3 hours you would eventually be waking up naturally later and later until you are out of sync with everything around you).

 To keep in sync with the external environment your body clocks entrain to the solar clock as you said. To prevent too much information, you have a master circadian clock in the suprachiasmatic nucleus (the SCN) which is a structure in your hypothalamus coordinating all of your peripheral body clocks in each cell. The action of the SCN is directly controlled by light. 

Thus, for a quick answer, your body cells are an orchestra and the SCN is a conductor keeping them in check. Each cell knows what time they think it is and runs accordingly, but the solar clock is used to keep re-adjusting the actions of each cell to match the changing external environment.