The shortest days and their dark secrets
The two longest nights of the year last from 4:54 p.m. to 7:18 a.m. That’s 14 hours, 24 minutes each. The actual “Thomas Night” is from December 20th to December 21st. According to astrophysicists, however, it is only about 30 seconds longer than the following.
In the days, weeks and months that follow, the days not only get longer again. The daily increase in daylight increases from day to day – until spring, when it is equinox. After that, the daily increase in light decreases again and turns into the opposite at the summer solstice on June 21st – towards autumn and winter. Experts describe the overall system with a sine curve.
Dark mornings make winter nights long
Astronomical backgrounds at the time of the winter solstice astonish many laypeople if they find out about it: The beginning of dusk at 4:52 p.m. (Salzburg time) has been constant since December 4th to 16th. In these two weeks since the beginning of the month (!), The days in their evenings were no longer getting any shorter.
On December 16, this situation shifted towards spring for the first time – by one minute to 4:53 p.m. Today on Monday evening (December 20), dusk is at 4:54 p.m. – again 60 seconds longer. Soon we have two minutes of daily change, later even more.
Sine Curve & Ellipse
Why don’t the times of day or twilight change constantly and more clearly?
The earth does not move in the equatorial plane and does not move on a circular path with constant angular velocity around the sun. But in the ecliptic – according to Kepler’s laws – on an elliptical orbit. Thus, the annual orbit of the projection of the direction of the sun takes place at a variable angular velocity. Therefore, the hour angle of the sun lying in the equatorial plane changes unevenly – even with the theoretical assumption of a constant rotation speed of the earth.
Lighter evenings since December 16th
In the mornings the situation looks very different. Their reversal for shorter nights only begins here on January 6th. On this day we still have the latest dawn of the whole year: 7.21 a.m. (Salzburg). However, this value will only be reached on December 30th (!) And will then remain the same for a whole week.
These changes in light, darkness and their transitions are anything but linear to one another and to one another between December 16 and January 6. In general, the following applies to the shortness of the days around the winter solstice, the late morning dawns are much more the cause than the early evenings.
Examples
The night from 16 to 17 December lasts from 4:53 p.m. to 7:15 a.m. (Salzburg time). That’s 14 hours, 22 minutes.
The night from 5th to 6th January lasts from 17.06 to 7.21 a.m. That’s 14 hours, 15 minutes.
Regionally strongly dependent on longitude
All times of the day mentioned here apply to the city of Salzburg and points in the surrounding area that are on the same longitude – with generous regional deviations – for example Gastein or the Innviertel have the same times as Salzburg.
Footnote: For Vienna you should always add 15 minutes. Day, night and twilight come to Vienna a little earlier: the earth turns from west to east, and Vienna is east of Salzburg.
For Innsbruck, from the point of view of Salzburg, six minutes would have to be deducted from all information, because day and night always come to Innsbruck a little later.
Aviation basics
All points in time in this story are based on regulatory data for aviation. Twilight times and their annual course are published in separate tables for all airports around the world. In many areas of aviation, daylight and the visibility of objects in space and on the ground play central roles – especially in traffic according to visual flight rules (VFR), but also for landing approaches according to instrument rules (IFR).
Technical terms, definitions
- for the end of daylight:
ECET = End of civil twilight = end of “civil twilight” = point in time at which the center of the solar disk is six degrees below the mean horizon.
BCMT = Beginning of civil dawn = Beginning of “civil dawn”, when the center of the solar disk is.
ECET and BCMT are given by authorities, governments, scientists and pilots in “Universal Time” (UTC). For Salzburg this is one hour after local time in winter and two hours in summer. UTC runs as a year-round fixed time standard that – starting from Greenwich near London – is globally gold-plated. World time has its historical roots in the epochs, as British centuries ago, as British centuries ago. At that time, the nautical mile or nautical mile (1,851 kilometers) was also created as a unit of measurement. SHE is the exact distance if you cover exactly one angular minute on the 40,000 km long equator while circumnavigating the earth (360 degrees).
Similar to Jewish Shabbat tradition
Similar, not quite as complex tables about daily changes in the length of the day have been in traditional Judaism for many centuries – for private households, but also for synagogues. It is ritually about the beginning of all holidays. It is especially true on Fridays, IF EVERY week at sunset or at dusk the candles are lit for the following day of rest Shabbat.
Tradition and modernity
A Shabbat lasts from sunset on until dark on the following Friday. In the calendar of Jewish tradition, every day runs from the evening before until the evening of the next day – and not from midnight to midnight.
Hanna Feingold, President of the Israelitische Kultusgemeinde Salzburg, sees strong cross-connections between tradition and modernity, between religion and aviation in the twilight tables. This scientific closeness to God can be used with a wink in religious education for Jewish elementary school students, smiles the Salzburg native:
“If you don’t know when your Shabbat begins, ask a pilot. Unfortunately we no longer have any elementary school students in Salzburg. A few days ago, however, a family with three children registered with us. Perhaps that is the divine boost for our community of seniors. “