Time

[spaceboy]

I was surprised to read that Earth actually rotates every 23hrs & 56 minutes but we take it to the nearest 24th Hr for ease. Over a period of thirty years our seasons will have changed by one month as a result. I'm assuming those who have lived long enough to get a letter from the Queen may well have been sun bathing during mid December in their youth.

[Stu]

Isn't that what leap years and leap seconds are for? They correct for the fact that a year is roughly 365.25 days long.

Stu

[spaceboy]

Ahhh good point Stu. I had forgotten all about leap years

I see we are due one again this year. It's days like this I wish I had stayed in bed

Over a period of 4 years would this not have accumulated the equivalent to 4 days though??

[Ant]

I was watching a program about this a few nights ago... iot's more complicated than that!

Days are 23hr 56m long. We get around that by every four years having and extra day - a leap year.

But that over compensates ever so slightly. So every hundred years we DON'T have a leap year.

So 1996 was a leap year

2000 wasn't

2004 was

2008 was etc etc etc

I hops that I've remembered it correctly... in fact now that I've written that down it may have been every 400 years (not 100) that we miss out the leap year.

I'm sure that someone will be along shortly with a better memory than me

Cheers

Ant

[Stephen]

If you like the math ...

Why we have leap days | Bad Astronomy | Discover Magazine

[Saleratus]

I laughed when I read that we take the rotation up to 24 hours for ease. How does that make sense? Where does the idea of "24 hours" come from. If this were really true, it wouldn't just throw of our months, it would throw off our days, and pretty soon, lunchtime would be in the middle of the night.

There's got to be a problem here, and I suspect it is that the earth rotates in 23 hours 56 minutes, and the other 4 minutes comes from the earth's natural rotation around the sun during the course of a year. It makes sense that your bit of the earth has to be facing the sun at noon every day, and this means that on one day of the year, it's going to be facing 180 degrees in the opposite direction at noon than it is 6 months later.

As for leap years, they come from the fact that the earth doesn't really travel around the sun in 365 days, and every 4 years we need to add an extra day to make up for this. There are other smaller adjustments made from time to time to keep things within a day or so of the proper season.

So since the introduction of the Gregorian Calendar, the earth doesn't wander off season, and is always within about a day of where it should be on its annual rotation.

[hemihaggis]

I was surprised to read that Earth actually rotates every 23hrs & 56 minutes but we take it to the nearest 24th Hr for ease. Over a period of thirty years our seasons will have changed by one month as a result. I'm assuming those who have lived long enough to get a letter from the Queen may well have been sun bathing during mid December in their youth.

Ant: removed post. Stop being rude.

[Stu]

Looks like you missed the one this year then Spaceboy, already been and gone :-)

Staying in bed sounds like a much more sensible thing to do :-). Makes it difficult to get out of the wrong side which seems to be a regular occurence for some ;-)

Stu

[spaceboy]

I laughed when I read that we take the rotation up to 24 hours for ease.

My bad! I am having one of those days and I often forget that some members on the forum are critical that posts have to be word perfect. Please ignore my Chinese whispers

Quote: From Stars and Planets By Igloo books.

PRECISE DAY

Clocks on Earth have a 24hr day. In fact, the Earth rotates in 23 hours 56 minutes 4 seconds, but this is so close to 24 hours that it makes no real difference. It dose mean that stars rise earlier by about 4 minutes each night. Over a week, stars rise earlier by about a half an hour. In a month it adds up to two hours.

[spaceboy]

Looks like you missed the one this year then Spaceboy, already been and gone :-)

Stu

:o:o:o I think I should quit while I'm behind

That will teach me to read my son's books again

[coulthamst]

My understanding is that the day with respect to the rest of the universe is 23 hrs 56 mins, but the "everyday" day (ie with regard to the position of the sun in our sky at 12.00 noon on successive days) takes 24 hours because of the earth circling the sun every year. Multiply 4 min by 365 will equal one day.

[Catanonia]

The maths is

Leap year every 4 years, but not if divisible by 100, but that is superceeded if it IS divided by 400.

I remember the old days of computer programming (unix days) when programmers didn't know what dates actually did and hence we had hundreds of different date formats in databases and as a reporting software company we had to deal with them all = Nightmare.