Circadian entrainment refers to the synchronization of your circadian rhythm—your internal 24-hour biological clock—with environmental signals called zeitgebers (German for “time givers”). The most powerful zeitgeber is natural light, but other cues include meal timing, physical activity, and temperature. Your brain’s suprachiasmatic nucleus (SCN), located in the hypothalamus, acts as the master clock. It receives information from the eyes and adjusts the timing of sleep, hormone production, and body temperature accordingly. When light hits the retina in the morning, it signals the SCN to suppress melatonin and increase alertness. As evening approaches and light decreases, melatonin levels rise, preparing your…