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Mid Summers day

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plugh
554874.  Sat May 16, 2009 12:21 am Reply with quote

If June 21 is the first day of Summer how is mid summers day June 24?

 
QiScorpion
554902.  Sat May 16, 2009 4:01 am Reply with quote

Someone with more knowledge of these things will explain it better than I can (and probably correct me in the process) but here's my contribution, which is an educated guess at best:

Midsummer's day is a pagan festival celebrated because it was the middle of what was summer to them - the pagans didn't have the Gregorian calendar to demarkate (sp?) the year, so midsummer was whenever the day was longest. It eventually became established that the longest day fell on a particular day every year, so they announced it as Midsummer's Day.

When the Gregorian Calendar came into being, it turned out that Midsummer's Day was June 24th.

Whenever BST was introduced, it was discovered that June 21st begins summer. the mix up, obviously, has never been corrected.



It doesn't sound like the best explanation but it's the best i've got and i sincerely hope someone else will do a better job than me.

 
3cheeseshigh
554903.  Sat May 16, 2009 4:02 am Reply with quote

Because Summer only lasts about a week, on average! We've just had our week, down here in the South-West of England, and now it's autumn - just look at that rain!

 
suze
555475.  Sun May 17, 2009 6:27 am Reply with quote

The summer solstice is the day when there is the longest gap between sunrise and sunset; that is usually on 21 June (as it will be this year), sometimes on 20 or 22 June.

It is not the same day as that day upon which sunset is at the latest hour; this year in London, that will be 27 June, when sunset will be at 2022 UTC (i.e. 2122 BST). Quite why the two things don't happen on the same day I don't really know; is it a consequence of the Earth not being perfectly spherical?

As suggested, the fact that the summer solstice does not coincide with the traditional understanding of Midsummer's Day is to do with calendar changes over the millennia.

 
plugh
555764.  Sun May 17, 2009 1:23 pm Reply with quote

I think my question may have been more basic. summer is June 21 to approximately September 21 (?). How can "Mid-Summers" day be so near the beginning of Summer.

 
Moosh
555766.  Sun May 17, 2009 1:31 pm Reply with quote

Summer is from the 21st of May to the 21st of August isn't it? Which would put Mid-summer's day just over a third of the way through.

 
mckeonj
555920.  Sun May 17, 2009 4:42 pm Reply with quote

You may also ask why 'Christmas Day', which is a midwinter festival, falls on 25th December and not on 21st December, which is the winter solstice. The answer to that is that 'Christmas Day' celebrates the return of the light as the days begin to lengthen some three or four days after the solstice.
There must be a similar reason for the marking of midsummer some three or four days after the solstice. It may have something to do with Christ being equated with the Lord of Light of pagan tradition.

 
djgordy
556011.  Sun May 17, 2009 6:13 pm Reply with quote

The midsummer and midwinter festivals go back thousands of years. At one time they would have corresponded with the solstices but no longer do so due to the precession of the equinoxes. That is, the vernal equinox and, hence, the solstices and autumnal equinox get slightly earlier each year. It takes 25,771.5 years for the vernal equinox to complete one complete cycle and get back to where it started.

Midsummers Day is one of the four quarter days, along with Michaelmas, Christmas and Lady Day. Midsummers eve is particularly associated with fairies being about, hence the plot of the Shakespeare play.

The reason that it is called "Midsummers Day" is that, in medieval times. summer was counted as starting on May 1st whilst February 1st was the first day of spring and so on.


Last edited by djgordy on Mon May 18, 2009 3:51 am; edited 1 time in total

 
Sadurian Mike
556012.  Sun May 17, 2009 6:14 pm Reply with quote

Isn't that when all the murders take place?

 
Davini994
556033.  Sun May 17, 2009 8:21 pm Reply with quote

suze wrote:
The summer solstice is the day when there is the longest gap between sunrise and sunset; that is usually on 21 June (as it will be this year), sometimes on 20 or 22 June.

It is not the same day as that day upon which sunset is at the latest hour; this year in London, that will be 27 June, when sunset will be at 2022 UTC (i.e. 2122 BST). Quite why the two things don't happen on the same day I don't really know; is it a consequence of the Earth not being perfectly spherical?

I've been researching this; it's about analemmas:



An analemma plots the path of the sun at the same time of day through the year. The summer and winter solstices are at the top and bottom of the above picture; the sun is apparently travelling West at these times. So the latest sunset is after Mid summer, and the latest sunrise is before mid winter.

There are two main things that cause the analemma:

1) the elliptical orbit of the earth around the sun.
2) the tilt of the earth

1) is the easiest to understand: because the path of the earth around the sun is orbital, it's angular speed is faster and slower at different times, meaning the sun is East or West of where we might expect it to be in the sky on clock time.

There's a nice video that shows this here.

The North South thing is due to the seasons; the sun appears higher in summer when the hemisphere leans towards the sun, and lower in winter when it leans away.

The tilt of the earth also effects the East-West apparent movement. has the same effect. It's hard to explain why. Larry:

Larry Denenberg wrote:
First let's examine the effect of the earth's rotation. Imagine an untilted earth not revolving around the sun, just rotating, and it's obvious that the sun-directly-overhead point moves along the equator, once around per day. It moves due west. If we measure speed in degrees of longitude per hour we realize that the speed of the point is constant, no matter what latitude it's at; it goes once around, 360 degrees, each day.

The rotation of the earth causes the sun-directly-overhead point to move directly west, crossing lines of longitude at a constant rate. If this were the only factor to consider, the length of the solar day would be constant regardless of the tilt.

Now we have to add the effect of the earth's revolution around the sun. Again, start by imagining the earth with untilted axis, this time not rotating but just revolving around the sun. You'll see the sun-directly-overhead point moving once around the earth each year. And the point moves eastward, so its motion is contrary to the motion from the rotation---when added in, this motion makes each solar day a little longer than it would be from the rotation alone. (But just a very little, since the motion from the revolution is so much slower.) If the earth were not tilted, the motion due to revolution would be due east at constant rate, and would lengthen each day equally throughout the year.

But the earth is tilted. So the earth's revolution around the sun doesn't carry the sun-directly-overhead point along the equator. It carries it around a great circle that wibbles back and forth with respect to the equator. The sun-directly-overhead point moves at a constant speed around this band. It moves generally east, but sometimes it's travelling a little north-east and sometimes a little south-east. It moves due east only at its most northerly and southerly extent, which happens at the solstices.


So the sun moves constantly on the ecliptic, which is at a variable angle to the equator. Days change with the rotation of the earth around the sun, but the effect of the earth's rotation about the sun isn't constant in the East West direction. So when we measure where the sun is at the same time on our constant 24 hour clock through a year, it is displaced either East and West depending on the season.

s: http://www.larry.denenberg.com/earliest-sunset.html
s: http://www.uwm.edu/~kahl/Images/Weather/Other/analemma.html
s: http://www.analemma.com/Pages/framesPage.html
s: http://www.qi.com/talk/viewtopic.php?p=417441#417441

 
suze
557686.  Wed May 20, 2009 7:09 pm Reply with quote

Thanks Dave, I think I just about understand that!

 
bobwilson
557688.  Wed May 20, 2009 7:15 pm Reply with quote

suze wrote:
Thanks Dave, I think I just about understand that!


Nerd!

 
Davini994
557819.  Thu May 21, 2009 9:54 am Reply with quote

Huzzah, someone is interested after all. It's a difficult thing to express, and I'm not sure I've done a very good job despite rewriting it several million times:(

 
Jenny
557825.  Thu May 21, 2009 10:05 am Reply with quote

That was well done, Davini. It's not easy either to explain or understand.

 
Starfish13
557830.  Thu May 21, 2009 10:21 am Reply with quote

but very very interesting. ta for links.

 

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