{"id":14245,"date":"2025-06-03T16:21:59","date_gmt":"2025-06-03T10:51:59","guid":{"rendered":"https:\/\/ibexaviation.com\/pilot-training\/?p=14245"},"modified":"2026-07-26T10:18:03","modified_gmt":"2026-07-26T04:48:03","slug":"year-day-measurement","status":"publish","type":"post","link":"https:\/\/ibexaviation.com\/pilot-training\/year-day-measurement\/","title":{"rendered":"Year and Day Measurement"},"content":{"rendered":"<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/general-navigation\/g22-year-day-time-1.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<h2>Year &#8211; Day &#8211; Time<\/h2>\n<p>A year is calculated based on the Earth&#8217;s revolution around the Sun, which takes about 365.25 days. A day is based on Earth&#8217;s rotation on its axis, taking approximately 24 hours. Time is calculated using Earth&#8217;s rotation, divided into hours, minutes, and seconds for navigation purposes.<\/p>\n<h3>Sidereal Year<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/general-navigation\/g22-year-day-time-2.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>A sidereal year is one complete revolution of the Earth around the Sun.<\/li>\n<li>A distant star (effectively at infinity) is used as the reference datum.<\/li>\n<li>The duration of a sidereal year is approximately <strong>365 days, 6 hours, 9 minutes, and 10 seconds<\/strong>.<\/li>\n<\/ul>\n<h3>Tropical Year<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/general-navigation\/g22-year-day-time-3.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>A tropical year is one complete revolution of the Earth around the Sun.<\/li>\n<li>It is measured relative to the Sun and the vernal equinox.<\/li>\n<li>The changing inclination (precession) of the Earth&#8217;s axis is taken into consideration.<\/li>\n<li>The duration of a tropical year is <strong>365 days, 5 hours, 48 minutes, and 45 seconds<\/strong>.<\/li>\n<\/ul>\n<h3>Calendar Year<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/general-navigation\/g22-year-day-time-4.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>A calendar year is designed to contain a whole number of days.<\/li>\n<li>A normal calendar year has <strong>365 days<\/strong> instead of 365 days, 5 hours, 48 minutes, and 45 seconds.<\/li>\n<li>Leap years include <strong>29 days in February<\/strong> to compensate for the additional quarter day accumulated each year.<\/li>\n<li>The calendar adjustment follows three rules:\n<ul>\n<li>Every fourth year is a leap year.<\/li>\n<li>Century years are not leap years.<\/li>\n<li>Every fourth century (years divisible by 400) is a leap year.<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<h3>Sidereal Day<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/general-navigation\/g22-year-day-time-5.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>A day is the time taken for one rotation of the Earth about its axis.<\/li>\n<li>Any celestial body may be used as the reference datum.<\/li>\n<li>A sidereal day is the time between two successive meridian transits of a distant star.<\/li>\n<li>The reference star is considered to be at infinity.<\/li>\n<\/ul>\n<h3>Usability of Sidereal Day<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/general-navigation\/g22-year-day-time-6.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>The Earth&#8217;s revolution around the Sun does not affect the sidereal day.<\/li>\n<li>Meridian transits referenced to a distant star remain constant.<\/li>\n<li>A sidereal day is not related to daylight or darkness.<\/li>\n<li>Therefore, the sidereal day is not suitable for everyday civil use.<\/li>\n<\/ul>\n<h3>Apparent Solar Day<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/general-navigation\/g22-year-day-time-7.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>An apparent solar day is the time between two successive meridian transits of the real Sun.<\/li>\n<li>The actual (apparent) Sun is used as the reference datum.<\/li>\n<li>An apparent solar day is slightly longer than a sidereal day.<\/li>\n<li>The Earth both rotates and revolves counter-clockwise when viewed from the North Celestial Pole.<\/li>\n<li>Between successive meridian transits, the observer&#8217;s meridian changes position due to Earth&#8217;s revolution.<\/li>\n<li>As a result, the Earth must rotate a little farther to bring the Sun back to the meridian.<\/li>\n<\/ul>\n<h3>Usability of Apparent Solar Day<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/general-navigation\/g22-year-day-time-8.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>The length of an apparent solar day varies from day to day.<\/li>\n<li>This variation occurs because the Earth&#8217;s orbital speed changes with its distance from the Sun.<\/li>\n<li>Consequently, the apparent solar day is unsuitable for practical timekeeping.<\/li>\n<\/ul>\n<h3>Mean Solar Day<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/general-navigation\/g22-year-day-time-9.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>A mean solar day is the average length of all apparent solar days.<\/li>\n<li>It is also known as the <strong>civil day<\/strong>.<\/li>\n<li>It is the time between successive meridian transits of the <strong>mean Sun<\/strong>.<\/li>\n<li>The mean Sun is an imaginary Sun assumed to move uniformly around the Earth, completing one revolution every 24 hours.<\/li>\n<\/ul>\n<h3>Mean Solar Day Calculations<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/general-navigation\/g22-year-day-time-10.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>The mean solar day is obtained by dividing the total length of a year by approximately <strong>365\u00bc days<\/strong>.<\/li>\n<li><strong>360\u00b0<\/strong> of Earth&#8217;s rotation = <strong>24 hours<\/strong>.<\/li>\n<li><strong>15\u00b0<\/strong> of rotation = <strong>1 hour<\/strong>.<\/li>\n<li><strong>1\u00b0<\/strong> of rotation = <strong>4 minutes<\/strong>.<\/li>\n<li><strong>15\u2032 (minutes of arc)<\/strong> of rotation = <strong>1 minute<\/strong> of time.<\/li>\n<\/ul>\n<h3>Equation of Time<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/general-navigation\/g22-year-day-time-11.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>The Equation of Time is the difference between apparent solar time and mean solar time.<\/li>\n<li>Mean solar day is the basis for measuring mean time.<\/li>\n<li>Mean time may refer to <strong>Local Mean Time (LMT)<\/strong> or <strong>Greenwich Mean Time (GMT)<\/strong>.<\/li>\n<li>The difference between mean time and apparent time varies with the Earth&#8217;s position in its orbit.<\/li>\n<\/ul>\n<h3>Mean Time and Equation of Time<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/general-navigation\/g22-year-day-time-12.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>When mean time shows <strong>12:00 noon<\/strong>, the real Sun is not always exactly on the local meridian.<\/li>\n<li>The maximum difference is about <strong>16 minutes<\/strong> in mid-November.<\/li>\n<li>At that time, the real Sun is approximately <strong>16 minutes behind<\/strong> the mean Sun.<\/li>\n<li>A second maximum difference of about <strong>14 minutes<\/strong> occurs in mid-February.<\/li>\n<li>At that time, the real Sun is approximately <strong>14 minutes ahead<\/strong> of the mean Sun.<\/li>\n<\/ul>\n","protected":false},"excerpt":{"rendered":"<p>Year &#8211; Day &#8211; Time A year is calculated based on the Earth&#8217;s revolution around the Sun, which takes about 365.25 days. A day is based on Earth&#8217;s rotation on its axis, taking approximately 24 hours. Time is calculated using Earth&#8217;s rotation, divided into hours, minutes, and seconds for navigation purposes. Sidereal Year A sidereal year is one complete revolution of the Earth around the Sun. A distant star (effectively at infinity) is used as the reference datum. The duration of a sidereal year is approximately 365 days, 6 hours,&hellip;<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"disable_featured_image":false,"footnotes":""},"categories":[324],"tags":[],"class_list":["post-14245","post","type-post","status-publish","format-standard","hentry","category-cpl-atpl-general-navigation"],"_links":{"self":[{"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/posts\/14245","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/comments?post=14245"}],"version-history":[{"count":1,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/posts\/14245\/revisions"}],"predecessor-version":[{"id":16640,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/posts\/14245\/revisions\/16640"}],"wp:attachment":[{"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/media?parent=14245"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/categories?post=14245"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/tags?post=14245"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}