h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Does anyone know the rate of change per day, that the days get shorter
in the UK, from longest day, to shortest.

This came up in a quiz the other day.

At a guess, I would say 0.005479452054795

I almost agree to Anonymouse, but I think it's more like 0.005479452053651...

Thankyou Anonymouse 0.00547945054795 and Thankyou Krisni 0.005479452053651, must be close to the amount day's get shorter, but if I give you my coordinates latidude 51º 32m 2s north, longitude 3º 58m 4s west does this make a difference?.

Not unless you have fewer or more days in a year than the rest of the world.

Now how did we get so close yet come up different?

Soory I know how anoynig the revial of "dead" threads is but do any of you know why after the winter solstice (in 1999 that was Dec 22, northern hemisphere) the time of sunrise contiues to get later, whilst the sunset time also gets later, the days ARE longer but dawn still takes about 10 days or so to start getting earlier?


Chris

Because of... THE EQUATION OF TIME.
http://www.saao.ac.za/sky/eqntime.html seems like a pretty full explanation.

Gosh, I see why you posted a link rather than trying to explain Cheers

Chris

At different latitudes the rate of change must be different - at the arctic circle for instance, the difference in length of day between the two solstices is much greater than at the tropic of cancer, but the time in which it has to reach the two extremes is exactly the same, therefore days must get shorter/longer at a much greater rate as you get closer to the poles. Also, I'm guessing that the length of day plotted as a graph over twelve months is a sine, then the closer you get to the extremes, the slower the rate of change, and the rate would be highest at the equinoxes when day and night are of equal length. Or not

But what of the fact that the poles have 6 months of not-quite-day and six months of not-quite-night? (Or so I'm told.)

'Nonnie

Well Nonnie, it's like having two drag racing strips, one of which is longer than the other. If you want to get to the finish line of the longer one in the same time as it takes to make the shorter, you have to accelerate faster. At the poles, the longest day and the longest night are both 24 hours long, whereas at the equator, every day of the year is 12 hours from sunrise to sunset. The further you get from the equator, the greater the difference between the longest and the shortest day measured from sunrise to sunset. Thing is, the time between solstices is exactly the same all over the world - 6 months, so the daily rate of change in length of day for a place closer to the pole will be greater than that for a place closer to the equator. I seem to remember that in London, between winter solstice and summer solstice, the sun rises and sets about 2 minutes earlier and later each day, whereas here in south Texas, it's only about 1 minute. My friend in the far north of Norway though, about 800 miles from the North Pole tells me that the sun rises about 9 minutes earlier each day. Am I explaining myself clearly? I usually don't.

Sure you are.. I just need to go visit that link.

'Nonnie

This website might be of interest to people in the conversation
http://www.fourmilab.to/earthview/
Click on whichever is your closest mirror site, then go to 'map of the earth showing night and day regions"

In London the difference is about 15 minutes per week. ie: in the autumn it gets dark 15 minutes earlier each week, and in the spring it gets dark 15 minutes later.

In Stockholm (same latitude as the Shetlands) it seems to be nearer 20-25 minutes each week.

The other thing that you may not notice if you do not have easy access to a western horizon is that sunset moves from the northern end of the western horizon in the winter, towards the southern end in the summer.

All of the above is true - changing times, directions, etc, for sunrises and the southern hemisphere. With of course that wierd thing that it still gets light later in the mornings for a while in the winter.

Can we have some sunshine now please?

Happy winter solstice everyone. To those of you in the southern hemisphere, enjoy the longest day of the year. To those of you in the north, the days can only get longer from here, and it'll be summer agian before you know it

Ah, the joys of spring.

'Nonnie