It is so dark this morning primarily because of the Earth's axial tilt and its orbit around the sun. As we move toward winter in the Northern Hemisphere (or toward winter solstice), the sun rises later in the day and sets earlier, resulting in darker mornings. This happens because the Earth's axis is tilted about 23.5 degrees, causing the sun to illuminate less of the northern hemisphere during this time of year. As a result, mornings stay darker for longer periods. Biologically, the darkness impacts the hormone melatonin, which promotes sleepiness and is produced more when there is less light. Melatonin production continues in the dark morning hours, making it harder to wake up and feel alert. Additionally, the "cortisol awakening response," a hormone spike that helps with alertness around waking, is less intense in darkness, so people feel less ready to start the day on dark mornings. Thus, dark mornings are a natural consequence of Earth's orientation relative to the sun and affect human alertness through hormonal responses tied to light exposure.