Summer Solstice

[theplayingmantis]

So its the summer solstive at 22.43 Saturday. i dont understand it though. when is the longest day, sunrise on the 20th to sunset or sunrise 21st to sunset?

as i understand it the 22.43 marks the time the northern pole is tilted most towards the sun?

can someone explain in idiots terms?

[Toltec]

My wife pointed out that it is a leap year so it is probably the 20th and will move further into the 21st over the next three years.

[havoc]

Toltec said:

My wife pointed out that it is a leap year so it is probably the 20th and will move further into the 21st over the next three years.

I like your wife.

[Eric Mc]

The longest day always gets a reset each leap year.

[MiseryStreak]

theplayingmantis said:

So its the summer solstive at 22.43 Saturday. i dont understand it though. when is the longest day, sunrise on the 20th to sunset or sunrise 21st to sunset?

as i understand it the 22.43 marks the time the northern pole is tilted most towards the sun?

can someone explain in idiots terms?

The solstices occur when the Earth’s axial tilt is aligned with the Sun, the equinoxes when it is perpendicular to the Sun. The North Pole points directly towards the Sun on the June or Northern solstice, which always falls on the 20th, 21st or 22nd of June. Although you’ll have to wait 183 years for the next June 22nd solstice - 2203, and the last one was 1975, so I’ll never see one. The exact date and time of the solstices and equinoxes change from year to year due to many different factors, including axial wobble and the interactions with the other planets, but it’s mostly due to the use of the Gregorian calendar, where we have 3 years of 365 days and 1 of 366, to average close to the tropical year length of 365.242199 days. The calendar is further refined by adding the odd leap second, the last one was 2016 but they average every 20 months.

So your lack of understanding is entirely justified, as the sunrise, sunset and length of day today and tomorrow are identical, with tomorrow’s length of day being only fractionally shorter.

[nammynake]

I find a graph always helps...

[Gandahar]

theplayingmantis said:

So its the summer solstive at 22.43 Saturday. i dont understand it though. when is the longest day, sunrise on the 20th to sunset or sunrise 21st to sunset?

as i understand it the 22.43 marks the time the northern pole is tilted most towards the sun?

can someone explain in idiots terms?

22.43 ?

[Gandahar]

havoc said:

Toltec said:

My wife pointed out that it is a leap year so it is probably the 20th and will move further into the 21st over the next three years.

I like your wife.

Get in the queue... preferably behind me.

[Gandahar]

MiseryStreak said:

theplayingmantis said:

So its the summer solstive at 22.43 Saturday. i dont understand it though. when is the longest day, sunrise on the 20th to sunset or sunrise 21st to sunset?

as i understand it the 22.43 marks the time the northern pole is tilted most towards the sun?

can someone explain in idiots terms?

The solstices occur when the Earth’s axial tilt is aligned with the Sun, the equinoxes when it is perpendicular to the Sun. The North Pole points directly towards the Sun on the June or Northern solstice, which always falls on the 20th, 21st or 22nd of June. Although you’ll have to wait 183 years for the next June 22nd solstice - 2203, and the last one was 1975, so I’ll never see one. The exact date and time of the solstices and equinoxes change from year to year due to many different factors, including axial wobble and the interactions with the other planets, but it’s mostly due to the use of the Gregorian calendar, where we have 3 years of 365 days and 1 of 366, to average close to the tropical year length of 365.242199 days. The calendar is further refined by adding the odd leap second, the last one was 2016 but they average every 20 months.

So your lack of understanding is entirely justified, as the sunrise, sunset and length of day today and tomorrow are identical, with tomorrow’s length of day being only fractionally shorter.

Good summation ! I like the way you kept it simple and did not introduce Relativity effects. Both General and Special.

[Baron Greenback]

Currant obliquity of the Earth (tilt) of the Earth 23°26'14'.

[Eric Mc]

Baron Greenback said:

Currant obliquity of the Earth (tilt) of the Earth 23°26'14'.

I'm not sure you are raisin a relevant point.

[Digger]

Eric Mc said:

Baron Greenback said:

Currant obliquity of the Earth (tilt) of the Earth 23°26'14'.

I'm not sure you are raisin a relevant point.

Please don’t be so insultana-ing!



I tried.

[Baron Greenback]

Eric Mc said:

Baron Greenback said:

Currant obliquity of the Earth (tilt) of the Earth 23°26'14'.

I'm not sure you are raisin a relevant point.

The right ascension, and hence the equation of time, can be calculated from Newton's two-body theory of celestial motion, in which the bodies (Earth and Sun) describe elliptical orbits about their common mass center. This is linked to the obliquity of the ecliptic and the latitude of the observer. Sorry haven't touched the maths of all this in 30 years since university days.

[WatchfulEye]

MiseryStreak said:

The solstices occur when the Earth’s axial tilt is aligned with the Sun, the equinoxes when it is perpendicular to the Sun. The North Pole points directly towards the Sun on the June or Northern solstice, which always falls on the 20th, 21st or 22nd of June. Although you’ll have to wait 183 years for the next June 22nd solstice - 2203, and the last one was 1975, so I’ll never see one. The exact date and time of the solstices and equinoxes change from year to year due to many different factors, including axial wobble and the interactions with the other planets, but it’s mostly due to the use of the Gregorian calendar, where we have 3 years of 365 days and 1 of 366, to average close to the tropical year length of 365.242199 days. The calendar is further refined by adding the odd leap second, the last one was 2016 but they average every 20 months.

So your lack of understanding is entirely justified, as the sunrise, sunset and length of day today and tomorrow are identical, with tomorrow’s length of day being only fractionally shorter.

Leap seconds are not for the fine tuning of the year, but for the fine tuning of the day.

An ephemeris day is defined as being 24 hours exactly (i.e. 86400 seconds). The official definition of a second was based on the astronomical definition which was standardised to 1/86400 of a day in 1900. However, due to continual slowing of the earth's rotation, a mean solar day is longer than 86400 seconds today.

Additionally, the rotation of the earth is not stable - changes in the distribution of mass (e.g. earthquakes, large storms, filling of large reservoirs) all result in random fluctuations to the rotation rate. To prevent the time of day from going out of sync with the solar day, the major time system UTC introduces leap seconds as needed to limit the discrepancy. These can be negative (i.e. one minute has 59 seconds) or positive (one minute has 61 seconds). However, due to the average rotation speed being longer than an official day, there has not yet been need for a negative leap second.

Leap seconds are added on an as required basis on the last days of June or December, and are announced 6 months in advance.

[theplayingmantis]

cheers for the info all!

[2 sMoKiN bArReLs]

Eric Mc said:

The longest day always gets a reset each leap year.

I suppose it's just a few seconds different if there's no leap year for eight years.