I believe there will be several years between the the last leap second and the next, as there was between December 31, 1998 and December 31, 2005. The IERS publishes a long-term prediction of the average rotation rate of the Earth, which they update in their Bulletin A each week. The August 6, 2020, issue of Bulletin A contains this line:
UT1-UTC = -0.2147 - 0.00010 (MJD - 59075) - (UT2-UT1)
UT2 captures the seasonal change in the length of day, so it can be
ignored for long-term estimates. The important number, therefore, is
-0.00010, which I will call the UT1 slope.
The June 9, 2016, issue of Bulletin A contains this line:
UT1-UTC = -0.1734 - 0.00147 (MJD - 57556) - (UT2-UT1)
Which has UT1 slope equal to -0.00147. Since then the value of UT1
slope has increased steadily to its present value. It is larger now
than it has been at any time since January 6, 2005, which is the oldest
issue of Bulletin A that I have been able to locate. Based on the
current value of -0.00010 I estimate that the next leap second will be
on December 31, 2025, an interval of 9 years, which is longer than the
previous long interval of 7 years.
I attach a chart of UT1 slope since January 2005.
John Sauter (john_sau...@systemeyescomputerstore.com)
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PGP fingerprint E24A D25B E5FE 4914 A603 49EC 7030 3EA1 9A0B 511E
UT1_slope.ods
Description: application/vnd.oasis.opendocument.spreadsheet
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