“On the day of an equinox, the geometric center of the Sun's disk crosses the equator, and this point is above the horizon for 12 hours everywhere on the Earth. However, the Sun is not simply a geometric point. Sunrise is defined as the instant when the leading edge of the Sun's disk becomes visible on the horizon, whereas sunset is the instant when the trailing edge of the disk disappears below the horizon. These are the moments of first and last direct sunlight. At these times the center of the disk is below the horizon. Furthermore, atmospheric refraction causes the Sun's disk to appear higher in the sky than it would if the Earth had no atmosphere. Thus, in the morning the upper edge of the disk is visible for several minutes before the geometric edge of the disk reaches the horizon. Similarly, in the evening the upper edge of the disk disappears several minutes after the geometric disk has passed below the horizon.”
In Grand Rapids we actually have 12 hours and 9 minutes of potential sunlight today. On the 25th, daylight and darkness are equal with 12 hours of each. After that the darkness takes over and we have more darks hour than sunny ones. So you still have a few more days to enjoy the last bit of excess daylight.
By the way, this is the time of year when the daylight shrinks the fastest. We are currently losing about 2 minutes and 53 seconds of daylight every day. The summer day with the most daylight gives us a whopping 15 hours and 21 minutes. In contrast we’re moving toward winter with the least amount of potential daylight. That day, near the winter solstice, only gives us a measly 9 hours and 1 minute of possible sunshine. Keep in mind that in Michigan, most of us never see the sun in winter because of all the cloudy days so I suppose it doesn’t really matter. At least we typically have more sun in the summer, when it matters most for the tourism and recreation industries.
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