Happy Solstice ED

[flocker spotter]

it is now officially midsummer

[Mick Mac]

It's the longest day. Is that mid-summer?

Is the shortest day, then mid winter?

[diable rouge]

I think the sun stays at it's highest point for about 2 weeks from today, after which the days then start getting shorter again. So should 'mid-summer' officially be in the middle of this period? Either way, for me the summer is June, July & August...

[rendelharris]

Midsummer is a bit of a redundant term these days as (I recall from very dry Old English lectures) it comes from the time when spring and autumn weren't recognised as seasons, so summer was anything that wasn't winter, i.e. between April and the beginning of October, which made the end of June (and the solstice) a sensible midpoint. Now summer is generally seen as being June, July and August, midsummer really comes mid-July, I suppose.

diable rouge - the sun doesn't stand still for a couple of weeks! Daylight gets shorter from now on - tomorrow will have three seconds less than today and daylight hours continue getting shorter by a few seconds per day until the winter solstice.

[diable rouge]

Quite right rendell, there's been a similar discussion about this on here in the past :)

What I should've said is that because the change is so very small i.e a few seconds around the solstice, the perception is that the days are standing still...ergo solstice.

Doesn't the rate of change speed up though? If it was only a few seconds each day, surely that wouldn't account for the loss of daylight we experience up to the winter solstice. I'm sure the rate of change gets up into the minutes...

[rendelharris]

Yes, sorry I meant the rate of change increases by a few seconds a day, it lengthens so that at the end of June we're losing fifty seconds a day, end of July three minutes a day - then it slows down a bit, end of August nearly four minutes a day, then after the autumnal equinox (September 23rd) the rate of loss slows until at the beginning of December we're only losing two minutes a day, and then at the winter solstice we start gaining again.

[uncleglen]

temperatures in the high 20s next week- that's midsummer alright- hosepipe ban next and we'll know it is truly summer!

[holloway]

Day length in summer is shorter than day length in winter, an average day length over 365 days is what Grenwich Mean Time (GMT) refers to.

A brilliant way to enjoy a hot summer day is to visit the Grenwich Royal Observatory, thoroughly recommended.

[rendelharris]

Days are the same length throughout the year - 24 hours! Except for the occasional December 31st when they have to add a quarter second or whatever. Otherwise, all days are 24 hours, otherwise all the clocks would have to be reset every day...

[Cardelia]

rendelharris Wrote:

-------------------------------------------------------

> Days are the same length throughout the year - 24

> hours! Except for the occasional December 31st

> when they have to add a quarter second or

> whatever. Otherwise, all days are 24 hours,

> otherwise all the clocks would have to be reset

> every day...

Well, strictly speaking this isn't true. The length of a day depends what your definition of a "day" is.

If you define a day as 'one complete rotation of the Earth's axis' then every day is the same length: 23 hours and 56 minutes. But then we get into trouble with defining other time periods like years and, over the course of centuries, things get seriously out of kilter. This is partly why the Julian calendar was abandoned in the 18th century in favour of the Gregorian calendar. It's also one of the reasons why Easter and Christmas are on different dates in Orthodox countries.

If you define a day as 'the time between consecutive high noons' then it (mostly) solves the problems with defining other time periods. But the Earth's orbit around the sun is slightly elliptical, therefore the speed at which it orbits the sun varies slightly. It also wobbles on its axis a bit, hence the period between consecutive high noons does actually vary by +/- 30 seconds every day. It also causes problems with clocks and watches because noon is supposed to be when the sun is at its highest position in the sky, but it almost always isn't. Today (22nd June), the time we define as noon (12:00:00 on a watch) is not the point at which the sun is at the highest point in the sky. That time is actually 13:02 on a watch. If you ignore the daylight savings, this means that the sun is actually at its highest position in the sky 2 minutes later than the watch says it should be. In October the discrepancy is about 17 minutes, so a noticeable difference. We don't correct our watches for this, we just live with it.

We now define a day as lasting exactly 24 hours, which is the time period between consecutive noons averaged across a whole year (hence the historical adoption of Greenwich Mean Time). Which is fine, but in the UK the last Sunday in March only lasts 23 hours and the last Sunday in October is 25 hours long. Plus, as you mentioned, we add leap seconds occasionally. So we can't actually say that all days are the same length because they're not.

[Seabag]

Now that?s an answer ☝️

[diable rouge]

Indeedy, a well written explanation...