Day and Night

[Dreamweaver]

Did you know that tommorow (22nd December 2006) is the Longest Day in the Southern Hemisphere?

Well what you probably did not realise that even though its the Longest Day from the 23rd the days get shorter but the Evenings continue to draw out later until the 6th January 2007 before they start to draw in again.

Why is this you ask?

Well its to do with the Earths rotation around the sun and the wobble in orbit that creates seasons!

Put it simply the South Pole will be pointing to the sun on 22nd December before starting its wobble back BUT the Earth will not be at its closest point to the Sun until January 6th. Which convincing someone in the Northern Hemisphere the sun is at its closest to the sun is not easy when they are 6ft under snow

Off course the reverse is true in June and July and until you really look into it you probably dont notice.

Well flightsim is a weird beast with duplicating sunrise/sunset by showing stars in the sky which dont actually appear until 30 minutes or so after sunset (Civil twilight its called)

Interesting huh

[Zöltuger]

so if the days get shorter and the evenings continue to lengthen, then it must be getting light pretty early?
actually i'll be able to check how early it is on sunday- my flight leaves at 0710

[Charl]

This thought jogs my memory about something Towerguy mentioned - the shadows from aircraft taxiing at NZAA went down the length of the aircraft near sunset.
OK except the taxiway points something like 250 deg true.
So you thought the sun sets in the west?
Uh uh only happens at the summer and winter solstice, the rest of the year it sets north of west (winter) and south of west (summer).
Even if the spherical geometry is a little hard to grasp, think of it as the longer path the summer sun needs to take to make the day longer, and vice versa.
Never too old to learn...

[towerguy]

I am putting together a little tutorial on this to show what and why - probably have it done just after xmas.

but the basic idea is - the sun appears to travel W - E and travels in summer progressively south till around the tropic of capricorn ie about 23.5S so at midday NZAA it appears roughly N but at sunset the position you are seeing the sun at is a great circle route approx 90-100 degrees around the globe - so the direction from NZAA is not just an east west problem its actually a great circle direction -

as I say after xmas is out of the way and I get a bit more time I will finish putting together a more graphical tutorial.

cheers and merry xmas everyone.

[Dreamweaver]

Found this little gem on Avsim

magdec.zip

Magnetic variation data calculated by FS2004 date back from 1993 and have significantly changed
(several degrees in some part of the world). Most charts now include runway, ILS and procedure headings based on 2005 magnetic variations.
FS2004 calculates magnetic variation using a special latitude/longitude table that is contained in the MAGDEC.BGL file

Thats a few degrees of magnetic variation change since 1993

[Charl]

Interesting, wonder if it changes in the same direction or wanders back and forth with time?

[Dreamweaver]

Did you miss the geography classes Charl

I was pointed to a article once from a Alaskan newspaper that stated that the drift of the magnetic pole which is created by the ball of molten iron beneath our feet, has changed its direction of movement. One of the effects is the areas that Aurora are visible are also changing which may be bad news for Alaskan Tourism in 50 years.

Found this article as well

http://archives.cnn.com/2002/TECH/space ... orth.pole/

[Charl]

The Aurora would be the least of their troubles if the field flipped, as it has in previous times.
Interesting, I didn't know it moved about that much right now.