The surprising science behind shorter summer days
Scientific research reveals that Earth has been spinning at a quicker pace, causing the days to be marginally shorter compared to previous years.
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Reno will lose at least 70 minutes of daylight this month as sunsets arrive earlier each night.
Daylight always shortens after the summer solstice in June, but AccuWeather meteorologists say the loss becomes most noticeable in September — the steepest drop of the year. In some northern U.S. cities, daylight will shrink by more than 100 minutes; in Alaska, over 190 minutes. The change builds toward the autumn equinox on Sept. 22, when day and night are nearly equal.
Here’s what to know:
Why do we lose daylight in the fall?
The reason we see variations in daylight throughout the year has to do with the tilt of the Earth’s axis and whether it is toward or away from the sun. There are two times during the Earth’s rotation of the sun over the course of a year that the axis of the Earth is tilted neither toward or away from the sun; we call them equinoxes.
The fall equinox happens in September, and this year it falls on Sept. 22 at 2:19 p.m. ET, scientists say. When it happens, if you happen to be along the Earth’s equator, you would be able to see the sun directly overhead at noon.
On the equinox, the “‘nearly’ equal hours of day and night is due to refraction of sunlight or a bending of the light’s rays that causes the sun to appear above the horizon when the actual position of the sun is below the horizon,” according to the National Weather Service.
Earth orbits the sun at an angle, so in the northern hemisphere, where the United States is, Earth is tilted toward the sun during summer and away during winter, while the southern hemisphere is experiencing the opposite. After the spring equinox in March, we experience lengthening days because the Earth’s axis is gradually tilting our hemisphere more toward the sun until it reaches maximum tilt, which we call summer solstice.
Then our hours of daylight shorten until we reach the fall equinox and the days and nights are roughly equal lengths. This shortening continues until winter solstice in December, when we’ll experience the shortest day and longest night.
How will the days change in September?
Daylight will be shorter by the end of September by an hour or more for many parts of the United States. Even in southern locations, more than 40 minutes is expected to be shaved off daytime, according to AccuWeather. Here’s how much daylight will be lost in some U.S. cities:
Miami: 43 minutesAustin: 52 minutesSan Diego: 58 minutesRaleigh, North Carolina: 64 minutesNew York: 77 minutesPortland, Oregon: 91 minutesInternational Falls, Minnesota: 102 minutes
Reno Gazette Journal Managing Editor Jeffrey Meehan contributed to this report.