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When Pope Gregory XIII briefly shortened the light-year in 1582, it led to navigational chaos and the loss of several Papal starships.
Hmmm now that I think about this a light year would be (should be) based on an average year, not what we observe in any given year.
365.2425 days. Different searches give different results but that's what I'm going with.
I would think that the best time period to use for a light year is whatever year definition has been used to date
Now let's work on the best second to use for the light second
idk, it feels more intuitive for it to be based on the mode (most common) year length (365) instead of the average year length (365.2425).
The boring answer is that in physics a year is just defined as the time it takes for the Earth to orbit the sun, they don't care about calendars and leap years
I would've said 365.25 days?
You'd be imprecise for civil timekeeping, but spot on for astronomy
The civil rule is it's a leap year if the year is divisible by 4, unless it is also divisible by 100 unless it is also divisible by 400
We saw the rules play out in 2000 (at least those of us over 23 saw it) which is a year divisible by 100 and by 400 so it was a leap year
Yours (and astronomy's) is Julian style "if it's divisible by 4"
I prefer the newer calendars, where there is no good mental calculation for leap years - it's a leap year when the computer says it's a leap year
I almost certainly won't be alive for it, but it's funny to think about how confused people are going to be when 2100 isn't a leap year.
Interestingly, Wikipedia says they actually did base it on 365.25 instead of the actual 365.2425, so you’re technically right.
I don't think that is what Wikipedia says. Whatever one's thoughts on Wikipedia, I'm pretty sure it is getting this right.
365.25 is what you get if you have leap years every four years with no exceptions. This is what was done in the Julian calendar which was used in the Christian world some centuries ago (how long exactly depends on what part of the Christian world).
365.2425 is the average year length in the Gregorian calendar which we use (where leap years are 1592, 1596, 1600, 1604, 1608, ... 1692, 1696, 1704, 1708, ..., 1792, 1796, 1704, 1708, ..., 1892, 1896, 1904, 1908, ... 1992, 1996, 2000, 2004, 2008, ..., 2092, 2096, 2104, 2108, ...).
The actual average solar year is better approximated by the latter than the former, but it is still slightly off.
This seems pretty definitive to me:
As defined by the International Astronomical Union (IAU), the light-year is the product of the Julian year (365.25 days, as opposed to the 365.2425-day Gregorian year or the 365.24219-day Tropical year that both approximate) and the speed of light (299792458 m/s).
That is pretty much what I said. I was irritated by your wording "the actual 365.2425", which is just another approximation of the "actual" solar year.
Ah, gotcha, yeah fair enough, I could have said “more accurate”
They skip leap years every now and then. And then skip the skip. Etc. The rotation of the earth around the sun and the spin of the earth on its axis simply don't line up into a nice number.
Oh okay. Yeah I only have that rule of "every 4 years" in my head. I did some other programming exercise way back where we had some other rule, but I was thinking that it would end up being the same.
No, years divisible by 100 aren't leap years, except if they're also divisible by 400.
Oh right, I had some programming exercise about this, way back.
what is this, some sort of FizzBuzz calendar?
Why not redefine lightyears to include a leap year every four years. Except when the number ends on 00, but only if it is not divisible by 400. Physics would be so much easier!
Well it's in fact easy to calculate...
To make it easier to visualize we'll start with year 400. From year 400 to year 799 you've got a leap year every 4 years except for years 500, 600, 700 and including year 400, so that's 25 leap years for the first century and 24 for the others.
So you've got 25 + (3x24) = 97 leap years
And 75 + (3 x 76) = 303 non leap years
(97 x 366) + (303 x 365) = 146097 days every 400 years which means a year is 365.2425 days long on average.
365.2425 x 24 = 8765.82 hours on average
8765.82 x 60 x 60 = 31 556 952 seconds per year on average
31 556 952 x 299 792 458 (speed of light per second) = a light year is 9460536207068016 meters long or 9460536207068.016 km long when adjusted to take leap years into consideration.
Okay, but now whenever you state one light year, it's just a normal year. When you state four, it is three normal ones and one leap year. So four times one light year would not equal four light years.
You asked for a lightyear adjusted based on leap years, I provided the number. It's a bit more than 365 light days and a bit less than 366 light days, it's closer to the real distance covered by light during the time the earth goes around the sun.
Edit: Don't know why anyone would downvote me for providing what OP asked for in the first place, especially when their reply didn't really make sense in the context...