In the Dark

Just a quick note to point out that the Winter Solstice in the Northern hemisphere happens tomorrow, Friday 22nd December 2023, at 4.27 am CET (3.27 UT). I am posting this in advance as although I am will be getting up quite early to catch a flight, it won’t be that early…

People often think that the Winter Solstice is defined to be the “shortest day” or the “longest night” of the year. The Solstice is actually defined in astronomical terms much more precisely than that. It happens when the axial tilt of the Earth away from the Sun is greatest, so that the Sun appears in the sky with its lowest maximum elevation. The timing of this event can be calculated with great precision.

In Barcelona, sunrise today (21st December) is at 8.13 am and sunset at 5.24 pm, while tomorrow the sunrise is at 8.14 am and sunset at 5.25 pm. The Solstice therefore occurs before sunrise tomorrow morning and the interval between sunrise and sunset tomorrow will be very close to that today; the interval between sunrise and sunset on 20th December (yesterday) was four whole seconds longer than on 22nd (today); the shortest day is therefore today rather than tomorrow. Moreover, the Solstice marks neither the latest sunrise nor the earliest sunset: sunrise will carry on getting later until the new year, the length of the day nevertheless increasing because sunset occurs even later. For a full explanation of this, see last year’s Winter Solstice post.

This entry was posted on December 21, 2023 at 12:53 am and is filed under The Universe and Stuff with tags Earliest Sunset, Latest Sunrise, Solar noon, Winter Solstice. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.