When is a day not a day?

[Jonmo1]

This brings up something I've always wondered.
If it's actually 365.24 days per year, and we just do 366 every four years to make up the difference...

Why then is it not Dark outside at 1AM this year, then Daylight at 1AM 2 years later, then back to dark 2 years after that, and so on??

 

[Greg Truby]

...Why then is it not Dark outside at 1AM this year, then Daylight at 1AM 2 years later, then back to dark 2 years after that, and so on??

That's more or less what I was trying to figure out in my post #7 here. I think I may be completely missing Emma's question, though.

 

[cornflakegirl]

My colleague found this.

jonmo - my brain hurts even more now. Greg - apologies for completely missing what you were getting at!

 

[snowblizz]

This brings up something I've always wondered.
If it's actually 365.24 days per year, and we just do 366 every four years to make up the difference...

Why then is it not Dark outside at 1AM this year, then Daylight at 1AM 2 years later, then back to dark 2 years after that, and so on??

I don't know if it matters, but it's not only +1 day every four years. There are a couple of other "rules" to more finely adjust it. I forget them exactly, but even centuries and those divisible with 4 or something like that are/are not leap years to get it all adjusted correctly.

There's also leap seconds inserted to keep the day at the "correct" length apparently.
Don't know if it helps but this seems to be explaining a lot:
http://en.wikipedia.org/wiki/Day

 

[malteaser]

I'm the confused (and now less confused) colleague!!

I think I've figured this out. If you were looking from the sun then you'd see the earth rotate 365.24 times per year.

If you were floating on Jupiter then you'd actually see the earth rotate 366.24 days per year.

To look at it another way; it depends on you definition of rotate. If the earth behaved like the moon did around the earth then looking down at the North pole, it would rotate once, but looking from the sun it wouldn't rotate at all.

So it's a matter of your position (or your opinion) that decides whether the earth rotates an extra time.

Somoene else said this:
If it's actually 365.24 days per year, and we just do 366 every four years to make up the difference...

Why then is it not Dark outside at 1AM this year, then Daylight at 1AM 2 years later, then back to dark 2 years after that, and so on??

If I'm understanding the question correctly then if we used a solar year, this would happen. i.e. the year after a leap year should end at 6am on 1/1/xx. the next year it would end at mid-day on 1/1/xx and so on. Therefore we cheat the Science and restart our year 6 hours early (to coincide with the spinning of the earth or the definition of a day), then make up for it every 4 years on Feb 29th.

My Conculsion:
Secondary school Science wasn't that simple after all!!
(and perhaps this year I'll celebrate the new year a few hours later!!!)

 

[Greg Truby]

Correct Malteaser. Or to answer Jonmo's questions another way - it doesn't happen because a year doesn't equal a year:

1 vernal equinox to the next <> 1 complete orbit.

Because our calendars use the former, we must use the leap years to resync them to the latter.

 

[Wayne Duncan]

Strange how the mind makes connections. For some reason this thread brought to mind to old puzzle; " if you walk around a tree and a squirrel keeps himself on the opposite side of the tree (as squirrels are wont to do), after you complete a complete 360 degree revolution around the tree, have you walked around the squirrel?"

 

[sous2817]

Correct Malteaser. Or to answer Jonmo's questions another way - it doesn't happen because a year doesn't equal a year:

1 vernal equinox to the next <> 1 complete orbit.

Because our calendars use the former, we must use the leap years to resync them to the latter.

What I can't wrap my head around is....We don't make up time over the course of the year(s), we do it in one lump some on Feb 29th. So 2 years in to a leap year cycle, when we've presumably lost 12 hours (or there about) of time, why isn't night and day reversed?

 

[Jonmo1]

What I can't wrap my head around is....We don't make up time over the course of the year(s), we do it in one lump some on Feb 29th. So 2 years in to a leap year cycle, when we've presumably lost 12 hours (or there about) of time, why isn't night and day reversed?

I think I get it...

These are 2 different measurments of time.

1. How long it takes the earth to spin on it's Axis = 1 Day
2. How long it takes the earth to orbit the Sun = 1 Year

Those are 2 completely different and unrelated measurements of time..(i said it again because it's worth repeating).
They ARE NOT directly related to each other.
We Humans as a species over time have decided to correleate those 2 things together.
We collectively decided that 365 Days = 1 year.
But technically that is not correct.

The "extra day" is related to how long it takes to orbit the sun, it has nothing to do with how long it takes the earth to spin around on it's Axis.

Year 1, we spin on our axis 365 times, but we have not completely orbited the sun. There is a small gap left in that complete circle
Year 2, we spin on our axis 365 more times, and that small gap got a little bigger
Year 3, we spin on our axis 365 more times, small gap gets even bigger
Year 4, we spin on our axis 365 more times, small gap got big enough to = 1 day, so we put an extra day in the year.



Clear as Mud right?

 

[cornflakegirl]

Because the correction for the length of a year is about keeping the seasons in sync (because of the tilt of the earth), not about day and night. Consider the Islamic or Jewish calendars - the number of days in a year doesn't equal a full solar year. And so the months (and festivals) move about (and I think from time to time an extra month gets slotted in to restore balance). Makes no difference to daytime (when we are facing the sun) and nighttime (when we are pointing away).

[EDIT: or what Jonmo said]