DUT UT1

Finally stabilizing...

Just got my AA 2022 today.?ÿ

@john-hamilton?ÿ

So we are traveling about 18.5 miles/second around the sun. When we need to add a leap second, does that mean our orbit around the sun is slowing and it is taking us longer? Can they really use the stars to triangulate our position in space within 18 miles?

@lurker Oh no. Earthƒ??s rotation has minor variations. And the SI second doesnƒ??t quite match earthƒ??s rotation. When leap seconds are added yearly, the LOD (length of day) is farther out from SI second. Conversely, when leap seconds are not added itƒ??s because earthƒ??s period of rotation more closely matches SI second. The length of the tropical year is far more constant.?ÿ

Larry you got me to educate myself on the tropical year vs sidereal year vs earth's rotation and precession of the equinoxes and the cesium atom definition of a second. Cool stuff.

@lurker This what blogs are for.

btw, I had the same question about leap second and length of year a while back. I emailed NIST with the question and got a nice long response.?ÿ

@lurker And sidereal day. Sidereal time. Right ascension. GHA LHA. Yeah, itƒ??s not hard, but itƒ??s easy yo forget?ÿ

So does that mean there is only one double click on WWV after the top of the minute? It's been a while since I listened to it.

@shawn-billings I assume so.?ÿ

@shawn-billings I just listened. The tick for second 9 is doubled.

One double on the 9th agrees with the description. (I mistakenly thought it was (+) for 1-7 secs, and (-) for 8-15 seconds. So I learned something.)

ƒ??If you need UT1 with an uncertainty of 0.1 s, you can apply a correction to UTC. UT1 corrections are encoded into the broadcasts by using doubled ticks during the first 16 s of each minute. You can determine the amount of the correction (in units of 0.1 s) by counting the number of doubled ticks. The sign of the correction depends on whether the doubled ticks occur in the first 8 s of the minute or in the second 8 s. If the doubled ticks are in the first 8 s (1-8) the sign is positive. If the doubled ticks are in the second 8 s (9-16) the sign is negative. For example, if ticks 1, 2, and 3 are doubled, the correction is +0.3 s. This means that UT1 equals UTC plus 0.3 s. If UTC is 8:45:17, then UT1 is 8:45:17.3. If ticks 9, 10, 11, and 12 are doubled, the correction is -0.4 s. If UTC is 8:45:17, then UT1 is 8:45:16.6. If none of the ticks are doubled, then the current correction is 0.ƒ?

Thank you for adding that. It's been a long time since I've listened. Good memories.

Here is a book review I wrote awhile back.?ÿ I've forgotten a bunch in 13 years.

Larry Scott;?ÿ In the latest bulletin there will be NO leap second added at the end of June 2022 also.

?ÿ

JOHN NOLTON