{"id":16801,"date":"2017-01-04T14:55:47","date_gmt":"2017-01-04T19:55:47","guid":{"rendered":"http:\/\/mjtsai.com\/blog\/?p=16801"},"modified":"2017-01-04T14:55:47","modified_gmt":"2017-01-04T19:55:47","slug":"the-leap-second","status":"publish","type":"post","link":"https:\/\/mjtsai.com\/blog\/2017\/01\/04\/the-leap-second\/","title":{"rendered":"The Leap Second"},"content":{"rendered":"

Jack Forster<\/a>:<\/p>\n

UTC used to be based on the rotation of the Earth around its axis, as observed at Greenwich. Once upon a time – a simpler, happier time – the second was exactly 1\/86,400 of a day. By the mid-1950s, however, clocks had gotten accurate enough that we’d figured out that the Earth’s rotation on its own axis was irregular, so in 1952, the International Union Of Astronomers decided to define the second as a fraction of one orbit of the Earth around the Sun: a second would now be 1\/31,556,925.9747 of a tropical year.<\/p>

However, the year turned out to have the same basic problem as the day; it’s irregular, changing slightly in length from one year to the next. (This is different, by the way, from the problem that requires the insertion of an extra day in a Leap Year; the Leap Year is inserted to keep the Gregorian Calendar in sync with the seasons, but the reason for the Leap Year, is that there isn’t a whole number of days in a year, not that an astronomical year varies slightly in length from one year to the next.)<\/p>

[…]<\/p>

As it turns out, atomic clocks are much more stable than the Earth’s rotation around its axis, or its orbit around the Sun, and it soon became clear that while an atomic clock-based time standard (UTC) was great to have, it meant that there was going to be a cumulative difference between UTC, and observed mean solar time. While both the astronomical day, and year, are irregular, the day overall has been getting slightly longer for at least the last few centuries. To keep UTC and mean solar time in sync, a Leap Second is occasionally added to UTC.<\/p><\/blockquote>\n

Via Nick Heer<\/a>:<\/p>\n

\n

Accurate time is also essential for things like HTTPS certificates and, apparently, Cloudfare’s CDN services<\/a>.<\/p>\n<\/blockquote>\n

Previously: Intercalation<\/a>.<\/p>","protected":false},"excerpt":{"rendered":"

Jack Forster: UTC used to be based on the rotation of the Earth around its axis, as observed at Greenwich. Once upon a time – a simpler, happier time – the second was exactly 1\/86,400 of a day. By the mid-1950s, however, clocks had gotten accurate enough that we’d figured out that the Earth’s rotation […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"apple_news_api_created_at":"","apple_news_api_id":"","apple_news_api_modified_at":"","apple_news_api_revision":"","apple_news_api_share_url":"","apple_news_coverimage":0,"apple_news_coverimage_caption":"","apple_news_is_hidden":false,"apple_news_is_paid":false,"apple_news_is_preview":false,"apple_news_is_sponsored":false,"apple_news_maturity_rating":"","apple_news_metadata":"\"\"","apple_news_pullquote":"","apple_news_pullquote_position":"","apple_news_slug":"","apple_news_sections":"\"\"","apple_news_suppress_video_url":false,"apple_news_use_image_component":false,"footnotes":""},"categories":[2],"tags":[432,364],"class_list":["post-16801","post","type-post","status-publish","format-standard","hentry","category-technology","tag-gps","tag-time"],"apple_news_notices":[],"_links":{"self":[{"href":"https:\/\/mjtsai.com\/blog\/wp-json\/wp\/v2\/posts\/16801","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/mjtsai.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/mjtsai.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/mjtsai.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/mjtsai.com\/blog\/wp-json\/wp\/v2\/comments?post=16801"}],"version-history":[{"count":1,"href":"https:\/\/mjtsai.com\/blog\/wp-json\/wp\/v2\/posts\/16801\/revisions"}],"predecessor-version":[{"id":16802,"href":"https:\/\/mjtsai.com\/blog\/wp-json\/wp\/v2\/posts\/16801\/revisions\/16802"}],"wp:attachment":[{"href":"https:\/\/mjtsai.com\/blog\/wp-json\/wp\/v2\/media?parent=16801"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/mjtsai.com\/blog\/wp-json\/wp\/v2\/categories?post=16801"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/mjtsai.com\/blog\/wp-json\/wp\/v2\/tags?post=16801"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}