Earth will complete a full rotation in slightly less time than usual on Tuesday, July 22, making it one of the shortest days ever recorded.<\/p>\n
The difference will be just 1.34 milliseconds less than the standard 24 hours \u2014 not something you\u2019ll notice \u2014 but it\u2019s part of a puzzling trend in Earth\u2019s rotational behavior that has been unfolding in recent years. If it continues, a second may need to be subtracted from atomic clocks around 2029 \u2014 a so-called negative leap second, which has never been done before.<\/p>\n
The speed of Earth\u2019s rotation isn\u2019t fixed. Long ago, a day was much shorter than the 24 hours \u2014 or 86,400 seconds \u2014 we\u2019re now accustomed to. According to a 2023 study, a day on Earth was approximately 19 hours for a significant part of Earth\u2019s early history, due to a balance between solar atmospheric tides and lunar ocean tides.<\/p>\n
However, over deep time, a day on Earth has become consistently longer. The primary culprit has been tidal friction from the moon, which has caused it to gradually move farther away from Earth. As it moves away, the moon saps Earth\u2019s rotational energy, causing Earth\u2019s rotation to slow and days to lengthen.<\/p>\n
From when records began (with the invention of the atomic clock) in 1973 until 2020, the shortest day ever recorded was 1.05 milliseconds less than 24 hours, according to Timeanddate.com. But since 2020, Earth has repeatedly broken its own speed records. The shortest day ever measured occurred on July 5, 2024, when Earth\u2019s rotation was completed 1.66 milliseconds faster than usual.<\/p>\n
Looking ahead to 2025, scientists predicted that July 9, July 22, and Aug. 5 could be the shortest days of the year. However, new data suggests that July 10 took the lead as the shortest day so far in 2025, clocking in at 1.36 milliseconds less than 24 hours. On July 22, Earth is expected to complete its spin 1.34 milliseconds early, making it a close runner-up. If current predictions hold, Aug. 5 will be about 1.25 milliseconds shorter than usual, leaving July 22 as the second-shortest day of the year.<\/p>\n
There are signs the acceleration may be easing. The rate of decrease in day length appears to be slowing, but the underlying cause of the recent rotational changes remains elusive.<\/p>\n
One 2024 study suggested that the melting polar ice and rising sea levels may be influencing Earth\u2019s spin. However, rather than driving the acceleration, this redistribution of mass might be moderating it. A more likely culprit is deep below our feet \u2014 the slowing of Earth\u2019s liquid core, which could be redistributing angular momentum in a way that makes the mantle and crust spin slightly faster.<\/p>\n
\u201cThe cause of this acceleration is not explained,\u201d Leonid Zotov, a leading authority on Earth rotation at Moscow State University, told Timeanddate.com. \u201cMost scientists believe it is something inside the Earth. Ocean and atmospheric models don\u2019t explain this huge acceleration.\u201d<\/p>\n
Zotov predicts Earth\u2019s rotation may soon decelerate once again. If he\u2019s right, this sudden speeding-up could prove to be just a temporary anomaly in the planet\u2019s long-term trend toward slower rotation and longer days.<\/p>\n","protected":false},"excerpt":{"rendered":"
Earth will complete a full rotation in slightly less time than usual on Tuesday, July 22, making it one of the shortest days ever recorded. The difference will be just 1.34 milliseconds less than the standard 24 hours \u2014 not something you\u2019ll notice \u2014 but it\u2019s part of a puzzling trend in Earth\u2019s rotational behavior […]<\/p>\n","protected":false},"author":1,"featured_media":1343,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[54],"tags":[],"class_list":{"0":"post-1342","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-technology"},"_links":{"self":[{"href":"https:\/\/vanninet.com\/index.php?rest_route=\/wp\/v2\/posts\/1342","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/vanninet.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/vanninet.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/vanninet.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/vanninet.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=1342"}],"version-history":[{"count":1,"href":"https:\/\/vanninet.com\/index.php?rest_route=\/wp\/v2\/posts\/1342\/revisions"}],"predecessor-version":[{"id":1344,"href":"https:\/\/vanninet.com\/index.php?rest_route=\/wp\/v2\/posts\/1342\/revisions\/1344"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/vanninet.com\/index.php?rest_route=\/wp\/v2\/media\/1343"}],"wp:attachment":[{"href":"https:\/\/vanninet.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=1342"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/vanninet.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=1342"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/vanninet.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=1342"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}