2021: Early February, Equal Light, Darkness

Twilight
Twilight is the period of time before or after sunset when the upper atmosphere is illuminated by the sun that is below the horizon.

Depending on the latitude, the time of equal light and equal darkness occurs during early February.  This is not a mis-statement of the Vernal Equinox that occurs on March 20.  At the equinox, daylight and nighttime are equally divided.

At my latitude (41.7°N), daylight and darkness are equal at 10 hours, 26 minutes.

I divide nighttime into three parts:  evening twilight, darkness, and morning twilight.

Twilight occurs before the sun rises and after the sun sets.  The sun is below the horizon, but its light illuminates the atmosphere in spectacular displays of changing prismatic colors.  Morning and evening phases together occur during 3 hours each day.

The length of twilight varies from season to season. During summer at the mid-latitudes, it can last over 4 hours total.

Darkness occurs when the sun is far enough below the horizon, at an angle that is at least 18°, so that the sky is as dark as it gets naturally.

After the Autumnal Equinox in September, daylight’s length shortens each day.  Near Halloween (October 30, 2020), the equal daylight, equal darkness day (10 hours, 26 minutes for each) occurred at my latitude.

From that date, daylight diminished to 9 hours, 8 minutes for several days around the Winter Solstice.  Daylight slowly increased.  During January daylight increased 37 minutes from New Year’s Day until month’s end.

On February 10, the equal daylight-darkness day occurs again.

During the 102 days when darkness was longer than daylight, the average length of the day was 9 hours, 36 minutes.  There is hardly any daylight to save during this period.

Daylight Saving Time is merely a work-time arrangement.  Proponents of year-round daylight time focus on work issues, rather than social impacts of a permanently-advanced clock. The references in the linked article state that following standard time is a better look at the issue.  Employers and other organizations can modify their schedules, should they want to provide leisure time during the evening hours.

Year-round standard time seems to be the better choice than flopping clocks back and forth to shift sunlight to evening hours or a permanently advancing the clocks.

During early February enjoy the days of increasing daylight!

For more about the planet during February 2021, see this article.

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Categories: Astronomy, Jeffsfavs, Sky Watching

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