Sunset Question

[INRM]

I've seen something which makes no sense.

Following the 12/22 or so, the sun sets later...

Yet on December 25th, I remember even at around 5:00 (possibly later), the sun was still not below the horizon, it was cloudy (storm-clouds over head).

Yet today, on Dec 28th, by 4:40 the sun was already below the horizon, by 5:00 it was seriously starten to darken, by 5:20 the sky was dark.

How the hell can that happen? How can the sun set LATER on the 25th, than on the 28th?

-INRM

 

[Paul C. Anagnostopoulos]

The pattern of sunrise and sunset times is not a simple thing, where sunsets are earlier and earlier until the solstice, and then later and later.

~~ Paul

 

[El Greco]

On the solstice day we have the shortest day (from sunrise to sunset). This is not necessarily the day where sun sets earlier than all days.

For Athens, these days were 6,7 and 8 of December, where the sun set at 17:05. The duration of light (including twilight before sunrise & after sunset) for these days was 10h38m, 10h37m and 10h35m respectively.

From the 9th of December, the sunset time is steadily going later and later, and will continue like this until the end of June. The duration of daylight though keeps decreasing until Decmber 21st. Practically, from December 17 to December 26, the duration of light is 10h31m (sunset is later everyday, but so is sunrise).

The above numbers are from a program I've made myself for calculating sunrise, sunset, moonrise, moonset, twilights and moonphases. Regarding your question, you don't remember well. Since you apparently are on the northern hemisphere, the sun on 28th did set later than the 25th (for Athens, Greece it was 2 minutes later).

 

[BillyJoe]

Why are the day of shortest sunlight (Winter Solstice) and the day of earliest sunset (Does it have a name?) not the same day?

 

[Skeptoid]

A good explanation can be found here.

 

[BillyJoe]

Thanks Skeptoid.

So its connected to the analemma - yes, of course, now that I think of it. I've read this link previously but in a different context.

BillyJoe

 

[Soapy Sam]

BJ- I recall quite a good field guide to suntime in Richard Graves' book "Bushcraft". Full of handy tips on how to start fires without matches,identify edible shellfish and the like. A must for every skeptical boy scout. (And it's echt-Aussie, so you can read it while standing upright).

 

[BillyJoe]

Sammy, you're a very funny boy.

Alas, the book is out of print so perhaps I'll just have to continue to pretend I understand the amalemmawhatychemecallit thing.

dag,
BillyJoe

 

[Soapy Sam]

I did the traditional "I know I've got that book somewhere" dance last night and finally found it in the mound corresponding to my travel section. I see I bought the book in Canada in June 1979!

(AARGH!)

"Graves was leader of the Australian Jungle Rescue Detachment, attached to the Far East Australian Air Force." (Quote from the cover blurb)

His description of the analemma etc is briefer than I remembered and less detailed than the link Skeptoid gave.
The book is great fun, though the astronomical stuff had to be sign-reversed for us upright types, which confused me as it was the first time I had encountered this.
(I know, I know, positional bigotry at it's worst. )

Graves gives ways to calculate corrected time and position from the sun using a knife, a few sticks and (less usefully)- a copy of the book with the analemma diagram in it, though this could be memorised.

Probably simpler these days with a cheap watch , a mobile phone and a GPS, which I guess, is progress. But great fun- and if you ever need to turn your garden into a lethal killing ground, or live off the bush, the book is quite indispensable.
If you spot a second hand copy, snap it up.

And on the subject of Down Under / far eastern astronomical phenomena, let me be the first to wish you a happy 2004. (I know you ain't there yet, but you're nearer than me and I plan to be up a hill when it comes, with neither mobile phone nor GPS.)

 

[BillyJoe]

Yes, 24 hours and a few minutes to go. And same to you Soapy Sam you am.