Shortest Day

[aclivity]

Tomorrow (21st December) is the shortest day of the year. When is the longest night - is it tonight, or tomorrow night, or are they the same length?

[The Purist]

Erm, if the day is the shortest and the night isn't the longest, what fills the gap??

Anyhow, a quick bit of Googlage reveals ...

The apparently odd behaviour of sunrise/sunset times near the winter solstice

The winter solstice is the time when the Sun reaches its southmost distance from the celestial equator and hence, in northern latitudes is the day when the Sun is lowest in the sky at noon. This is, naturally, the shortest day of the year in northern latitudes. To many people it seems odd, therefore, that the time of sunrise continues to get later in the day after the solstice.

The reason for this is that the Sun does not cross the meridian (when it is highest in the sky) at precisely noon each day. The difference between clock-defined noon and the time when the Sun is on the meridian is called the Equation of Time and represents the correction which must be applied to the time given by a sundial to make it agree with clock time.

There are two reasons why the Sun is not on the meridian at noon each day. The first is that the path of the Earth around the Sun is an ellipse, and not a circle. The second is that the Earth's equatorial plane and its orbital plane are inclined to one another. The two effects add together to yield the equation of time which can amount to some 16 minutes difference between solar and mean time.

The period when the equation of time is changing fastest in the whole year is very close to the winter solstice. It changes by 10 minutes from December 16 to January 5. This means that the time at which the Sun crosses the meridian changes by 10 minutes in this interval and also that the times of sunrise and sunset will change by the same amount.

Near the solstice the Sun's height in the sky changes very slowly and the length of the day also changes slowly. The rapid change due to the equation of time dominates the very slow change in day length and leads to the observed sunrise times.

[nigelH]

Originally Posted by aclivity

Tomorrow (21st December) is the shortest day of the year. When is the longest night - is it tonight, or tomorrow night, or are they the same length?

Times for my part of Sussex
SR SS
19th 08:00 15:53
20th 08:01 15:54
21th 08:01 15:54
22th 08:02 15:55

I make that both equal but my source doesn't do seconds.
nigelH

[Odin]

Tomorrow will find me celebrating at 12:23 at a very special place in Wiltshire...

[Helen F H]

Originally Posted by Odin

Tomorrow will find me celebrating at 12:23 at a very special place in Wiltshire...

The coming of light. Marvelous.

[The Purist]

Originally Posted by nigelH

Times for my part of Sussex
SR SS
19th 08:00 15:53
20th 08:01 15:54
21th 08:01 15:54
22th 08:02 15:55

I make that both equal but my source doesn't do seconds.
nigelH

http://www.schoolsobservatory.org.uk...s/sunrs_yr.htm

does length of day too:

date, sunrise, sunset, day length (all in decimal hours)

20/12/2004,8.149,15.977,7.828
21/12/2004,8.158,15.985,7.827
22/12/2004,8.166,15.994,7.828

so 21st is indeed the shortest - just.

[chrisch]

Originally Posted by The Purist

Erm, if the day is the shortest and the night isn't the longest, what fills the gap??

Cheese...

Days get longer tomorrow. Hurrah....

Chris

[NotDeadYet]

Anyone else fancy joining me in slaughtering a bull, munching a bowl of mandrake root, deflowering a vestal virgin or two and carrying out a minor conquest of Gaul?

It's about time Mithraism was rekindled. Good enough for the Romans...

Happy Solstice, everyone.

[Odin]

[quote=Happy Solstice, everyone.[/QUOTE]
Thank you! I will be celebrating, and giving thanks.

Any other YD mob at the stones tomorrow???

Paul/Odin/Woden = all the same!

[Helen F H]

Originally Posted by Odin

Thank you! I will be celebrating, and giving thanks.

Any other YD mob at the stones tomorrow???

Paul/Odin/Woden = all the same!

Nope, but i will be giving thanks in my own little way.