Free Spirits Rowing

Remember tomorrow is the Summer Solstice challenge folks. If you are like me it’s also an opportunity to put in your one and only HM of the year. I’m doing the row with an ex-colleague while we are both on FaceTime for a bit of banter and company. Not sure how that will go.


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It will go well I hope Jon.
I do normally attempt this, but rarely when it falls on a weekend.
Rowing otw in the morning and golf in the afternoon for me.

I'm slightly confused. Is it on the 20th or 21st?

Paul Victory wrote: ↑Fri Jun 19, 2020 8:28 pm I'm slightly confused. Is it on the 20th or 21st?

You’re right to be confused Paul. The challenge is in the 20th even though the Solstice is on the 21st

JonT wrote: ↑Sat Jun 20, 2020 5:13 am

Paul Victory wrote: ↑Fri Jun 19, 2020 8:28 pm I'm slightly confused. Is it on the 20th or 21st?

You’re right to be confused Paul. The challenge is in the 20th even though the Solstice is on the 21st

Fortunately, my son is currently studying for his A Levels, and has kindly advised me as follows:

In any given year, the June solstice occurs at the particular moment that the Earth is positioned in its orbit such that the North Pole is leaning most towards the sun, ie the sun is directly over the Tropic of Cancer.

Accordingly, any given solstice happens at the same moment everywhere on Earth.

This moment may therefore be on different dates, depending upon where you are in the world at that particular moment.

The 2020 summer solstice takes place on June 20 at 22.43 BST in the UK, although this date can vary between June 20 and June 22 depending on the year. The 2020 winter solstice in New Zealand, which occurs at the same moment in time, happens at 09.43 NZ time on Sun 21 June.

The exact date of each solstice in any given place may change by a couple of days due to the inherently approximated nature of our calendar system. Every year, the Earth takes exactly 365.256 days to complete one orbit of the Sun, but we approximate this by rounding down to 365 or up to 366. So, by reference to our calendar, the solstice occurs around 6 hours later than the previous year in non-leap years, and 18 hours earlier than the previous year in leap years.

In addition, the exact orbital and daily rotational motion of the Earth, such as the ‘wobble’ in the Earth’s axis, also contribute to the changing solstice dates.

Who knew? Not me, for sure...

That tidies that up then.

JonT wrote: ↑Sat Jun 20, 2020 4:46 pm That tidies that up then.

Apparently, he’s revising French tomorrow, if you want to get your questions in early...

Thanks Dave,

I read this just in time to celebrate the summer solstice on the exact right moment.
Didn't complete the challenge though cause my wife needed the study today. Where the C2 is also located. Not to sorry for that, better luck next year.

fkoene wrote: ↑Sat Jun 20, 2020 7:44 pm Thanks Dave,

I read this just in time to celebrate the summer solstice on the exact right moment.
Didn't complete the challenge though cause my wife needed the study today. Where the C2 is also located. Not to sorry for that, better luck next year.

Nights are drawing in...

yes this summer solstice challenge was yesterday...and i did it on a unusual timeslot...after 9 pm...did it on the bikeerg as a 2:30h ride with zwift, and also unusual because i rode alone on zwift on a hilly track...a little bit more bike erg meters than zwift meters...! sorry not rowing...but earned the c2 solstice badge

Well done to all to complete this despite the confusion (slightly strange that it remains a 21k challenge on 20th!) 32 Freespirits are currently shown as completing sucessfully. Pretty impressive in my opinion, particularly when compared with the 40 that completed the HM &/or FM challenge when we had 2 weeks rather than a single day!

- Iain

Claudius wrote: ↑Sun Jun 21, 2020 12:53 pm yes this summer solstice challenge was yesterday...and i did it on a unusual timeslot...after 9 pm...did it on the bikeerg as a 2:30h ride with zwift, and also unusual because i rode alone on zwift on a hilly track...a little bit more bike erg meters than zwift meters...! sorry not rowing...but earned the c2 solstice badge

Great effort Claudius, especially at such loooooow heart rates. Mine is sometimes that high when I am thinking about starting a warm up!

Dogma Dave wrote: ↑Sat Jun 20, 2020 4:17 pm Fortunately, my son is currently studying for his A Levels, and has kindly advised me as follows:

In any given year, the June solstice occurs at the particular moment that the Earth is positioned in its orbit such that the North Pole is leaning most towards the sun, ie the sun is directly over the Tropic of Cancer.

Accordingly, any given solstice happens at the same moment everywhere on Earth.

This moment may therefore be on different dates, depending upon where you are in the world at that particular moment.

The 2020 summer solstice takes place on June 20 at 22.43 BST in the UK, although this date can vary between June 20 and June 22 depending on the year. The 2020 winter solstice in New Zealand, which occurs at the same moment in time, happens at 09.43 NZ time on Sun 21 June.

The exact date of each solstice in any given place may change by a couple of days due to the inherently approximated nature of our calendar system. Every year, the Earth takes exactly 365.256 days to complete one orbit of the Sun, but we approximate this by rounding down to 365 or up to 366. So, by reference to our calendar, the solstice occurs around 6 hours later than the previous year in non-leap years, and 18 hours earlier than the previous year in leap years.

In addition, the exact orbital and daily rotational motion of the Earth, such as the ‘wobble’ in the Earth’s axis, also contribute to the changing solstice dates.

Who knew? Not me, for sure...

One thing about the above puzzles me. The time taken to complete one orbit of the sun is shown as 365.256 days. But my understanding of leap years is that they occur when the year is divisible by 4 unless the year ends in 00, in which case the year must be divisible by 400.

Assuming that’s correct, there will be 97 leap years in every 400 years. This works out as an average of 365.2425 days per year, which is .0135 days less than the time taken to orbit the sun. That will result in the loss of 1 day every 74 years on average and would mean that the adjustment when the Gregorian calendar was introduced is in the wrong direction.

Paul Victory wrote: ↑Mon Jun 22, 2020 5:40 am

Dogma Dave wrote: ↑Sat Jun 20, 2020 4:17 pm Fortunately, my son is currently studying for his A Levels, and has kindly advised me as follows:

In any given year, the June solstice occurs at the particular moment that the Earth is positioned in its orbit such that the North Pole is leaning most towards the sun, ie the sun is directly over the Tropic of Cancer.

Accordingly, any given solstice happens at the same moment everywhere on Earth.

This moment may therefore be on different dates, depending upon where you are in the world at that particular moment.

The 2020 summer solstice takes place on June 20 at 22.43 BST in the UK, although this date can vary between June 20 and June 22 depending on the year. The 2020 winter solstice in New Zealand, which occurs at the same moment in time, happens at 09.43 NZ time on Sun 21 June.

The exact date of each solstice in any given place may change by a couple of days due to the inherently approximated nature of our calendar system. Every year, the Earth takes exactly 365.256 days to complete one orbit of the Sun, but we approximate this by rounding down to 365 or up to 366. So, by reference to our calendar, the solstice occurs around 6 hours later than the previous year in non-leap years, and 18 hours earlier than the previous year in leap years.

In addition, the exact orbital and daily rotational motion of the Earth, such as the ‘wobble’ in the Earth’s axis, also contribute to the changing solstice dates.

Who knew? Not me, for sure...

One thing about the above puzzles me. The time taken to complete one orbit of the sun is shown as 365.256 days. But my understanding of leap years is that they occur when the year is divisible by 4 unless the year ends in 00, in which case the year must be divisible by 400.

Assuming that’s correct, there will be 97 leap years in every 400 years. This works out as an average of 365.2425 days per year, which is .0135 days less than the time taken to orbit the sun. That will result in the loss of 1 day every 74 years on average and would mean that the adjustment when the Gregorian calendar was introduced is in the wrong direction.

Years, years, years...

The average number of days in a Gregorian, calendrical or solar year is, as you have correctly calculated, 365.2425 days.

The figure of 365.256 days I gave refers to the sidereal year, being the time it takes for the sun to return to the same position with respect to the stars, which is slightly longer than a solar year.

To astronomers, a "year" is more commonly taken to mean the tropical year, which is the mean interval between eg summer solstices, ie the time taken for the sun to return to the same position with respect to Earth.

The tropical year therefore takes into account the precession of the Earth, and measures 365.242190 days, ie slightly shorter than a solar year.

A tropical year is around 20 minutes shorter than a sidereal year.

Accordingly, if you use the tropical figure rather than the sidereal figure in your calculation, then the adjustment afforded by the Gregorian system pans out the way you expected.

Thanks for the detailed explanation. I almost understand that, I think!

Brilliant