21 Mar 06
The seconds in a year are usually this: 86,400 (seconds in one day)
times 365.26 and that gives 31558464 seconds in a year. But is that the actual #? Can you get it down to milli or microseconds? I think it has been proven the earth speeds down and slows up a bit but how many days in a year? I can't believe its known only to 5 digit accuracy.
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21 Mar 06
Originally posted by sonhouse31,536,000,000 milliseconds in a year.
The seconds in a year are usually this: 86,400 (seconds in one day)
times 365.26 and that gives 31558464 seconds in a year. But is that the actual #? Can you get it down to milli or microseconds? I think it has been proven the earth speeds down and slows up a bit but how many days in a year? I can't believe its known only to 5 digit accuracy.
No idea what you're driving at.
21 Mar 06
Originally posted by sonhouseIt's amazing what google can do.
The seconds in a year are usually this: 86,400 (seconds in one day)
times 365.26 and that gives 31558464 seconds in a year. But is that the actual #? Can you get it down to milli or microseconds? I think it has been proven the earth speeds down and slows up a bit but how many days in a year? I can't believe its known only to 5 digit accuracy.
1 year = 365.242199 days
Also:
1 year = 3.1556926 × 10^10 milliseconds
21 Mar 06
4 edits
Originally posted by SJ247Actually we have three separate answers. I got 365.26 from an article on accurate clocks in the special issue of Scientific American on Time.
Odd, your answer means that mine is wrong.
I used an online unit of time conversion calculator. Maybe it used 365 days.
Thats pretty much what I was asking, what is the best number to cite for the number of seconds or milliseconds in a year. The article on clocks was interesting, now closing in on clocks accurate to one part in 10^18, an accuracy that would be able to time the entire life of the universe within a few milliseconds. One problem with such a clock however is how to transfer that timing accuracy to another clock of the same type, that is to say, how to synchronize the two. I used to work on atomic clocks at NASA, cesium beam, rhubidium beam and quartz standards. Now there is an atomic clock smaller than a grain of rice accurate to one part in 10^11!
If Xanth's # is correct, then there are 31,556,925,990 milliseconds in a year. Of course the spin of the earth isn't that accurate so that may be just an average of ten years or something.
I was trying to convert this into a more accurate measure of the light year, since C is fixed but everywhere you look you get a differant # for the length of the year. I even see differant #'s for C, 186282 MPS * 1.6=298051.2 KM/S, and others.
Wikopia gives C as EXACTLY = 299,792,458 meters/second and then says its Approx. = 186,282.397 MILES/SEC. Dividing those two makes
the mile = 1.609344 Km. So how accurate is THAT #?
22 Mar 06
Originally posted by sonhouseThat figure for the length of a mile in kilometres is the same as the one you get by typing "1 mile in kilometres" into Google. This makes sense as when you ask it for the number of miles in a light year it is likely converting to miles from metres. When you divided your answers you are just reversing this (at the same accuracy) and you will get the same answer.
Actually we have three separate answers. I got 365.26 from an article on accurate clocks in the special issue of Scientific American on Time.
Thats pretty much what I was asking, what is the best number to cite for the number of seconds or milliseconds in a year. The article on clocks was interesting, now closing in on clocks accurate to one part in 10^18, ...[text shortened]... .397 MILES/SEC. Dividing those two makes
the mile = 1.609344 Km. So how accurate is THAT #?
22 Mar 06
1 edit
353, 354 or 355 days — the lengths of common years in some lunisolar calendars
354.37 days — 12 lunar months; the average length of a year in lunar calendars
365 days — a common year in many solar calendars
365.24219 days — a mean tropical year near the year 2000
365.2424 days — a vernal equinox year.
365.2425 days — the average length of a year in the Gregorian calendar
365.25 days — the average length of a year in the Julian calendar; the light year is based on it is 31,557,600 seconds
365.2564 days — a sidereal year
366 days — a leap year in many solar calendars
383, 384 or 385 days — the lengths of leap years in some lunisolar calendars
383.9 days — 13 lunar months; a leap year in some lunisolar calendars
see: http://en.wikipedia.org/wiki/Year#Variation_in_the_length_of_the_year_and_the_day
and:
http://en.wikipedia.org/wiki/Light_year
22 Mar 06
2 edits
Originally posted by XanthosNZThat makes it 1,609,344 millimeters per mile. Divide by 63360 (# of inches per mile) and you arrive at the well known 25.4 mm/inch which makes that one self consistent anyway.
That figure for the length of a mile in kilometres is the same as the one you get by typing "1 mile in kilometres" into Google. This makes sense as when you ask it for the number of miles in a light year it is likely converting to miles from metres. When you divided your answers you are just reversing this (at the same accuracy) and you will get the same answer.
Using those numbers then, C=299,792,458,000 MM/sec. Divide by 1609344 gives C in MPS as 186282.3971 MPS.
Divide by 12, C= 1.180285268 E10 Inches per second. Ten digit accuracy.
23 Mar 06
Originally posted by sonhouseSonhouse, I'm curious now, what work did you do with the atomic clocks at NASA?
That makes it 1,609,344 millimeters per mile. Divide by 63360 (# of inches per mile) and you arrive at the well known 25.4 mm/inch which makes that one self consistent anyway.
Using those numbers then, C=299,792,458,000 MM/sec. Divide by 1609344 gives C in MPS as 186282.3971 MPS.
Divide by 12, C= 1.180285268 E10 Inches per second. Ten digit accuracy.
31 Mar 06
Originally posted by sonhouseyes, 3155846400 milliseconds in a year.
The seconds in a year are usually this: 86,400 (seconds in one day)
times 365.26 and that gives 31558464 seconds in a year. But is that the actual #? Can you get it down to milli or microseconds? I think it has been proven the earth speeds down and slows up a bit but how many days in a year? I can't believe its known only to 5 digit accuracy.
31 Mar 06
Originally posted by leisurelyslothSorry, I missed your post. I was on the Apollo project, at Goddard Space Flight Center in the years 70 and 71 working on Apollo timing and tracking, the timing part was the successful attempt to co-ordinate the timing of the reception of apollo (and subsequent space program projects) data to within 100 nanoseconds. That is to say, when a deep space probe of any kind is way out there and being tracked, say first by Goldstone, the time Goldstone gets to aquire the signal is limited to the time the probe is actually in line of sight. Once it goes over the horizon, another dish had better be ready to take up the slack and that slack window established by NASA was one hundred nanoseconds or one tenth of a microsecond. By now, it might be down to ten nanoseconds, not sure, but in order to do that NASA and all the downrange tracking stations needed to have all the timing co-ordinated to well under that one hundred nanosecond window. Thats where the timing part comes in. We had three kind of clocks, well four counting the mighty hydrogen clock, but at our humble tracking station we had three: a master whoopdidoo cesium beam atomic clock accurate to within (ATT) one second in 6,000 years and a Rhrubidium
Sonhouse, I'm curious now, what work did you do with the atomic clocks at NASA?
atomic clock accurate to within one second in a few hundred years as the primary BACKUP and a back up back up, a quartz clock accurate to within one second in a couple three years. I never saw anything but the cesium beam clock run myself, it never crapped out. Anyway thats what the timing part was. My job was called timing and TRACKING.
the tracking part was, on the apollo (of course Skeeter denies all this), how do you figure out exactly how far away the lunar craft is on a line going away from earth? So they had this transponder, a signal, a very special signal, was transmitted to the craft and the transponers job was simply to sling the same signal back to earth like a mirror reflection. So a complicated code was embedded in the signal, I mean, REAL complicated!, and when the signal got back to Goddard, the exact timing of the signals, the transmitted one and the reflected one, was compared. Due to the complicated nature of the signal, there was only one distance that a particular signal/reflection would match so that was the distance to the apollo, kind of like extending a long arse ruler into space and bringing the end back to earth, you then knew by comparing the ends, what distance the ship had to be.
Sorry to be so long winded about it, its not easy to condense into a few hundred words.
31 Mar 06
Originally posted by SchumiActually in this case, they modified the definition of the 'meter'
Exactly? Nothing is exact.
so the speed of light, considered a constant by many, so they sync together now. You just define the meter as being a number that
measures out 299, 792,458 meters is how far light goes in one second and the second is known to something like 10E-18: 1 or so,
and thats only the beginning. In about 5 years or so, the second will be defined within 10E-21:1, enough to time the whole expansion of the universe to within the width of your finger. Now THATS accurate.
So yep, the speed of light is DEFINED as 299,792,458 meters per second. Now you have a good standard for time and distance. Thats what its all about. Don.