{"id":336,"date":"2020-10-22T11:47:23","date_gmt":"2020-10-22T11:47:23","guid":{"rendered":"https:\/\/maritimesa.org\/nautical-science-grade-11\/?p=336"},"modified":"2020-10-22T11:47:23","modified_gmt":"2020-10-22T11:47:23","slug":"correction-for-semi-diameter","status":"publish","type":"post","link":"https:\/\/maritimesa.org\/nautical-science-grade-11\/2020\/10\/22\/correction-for-semi-diameter\/","title":{"rendered":"Correction for semi-diameter"},"content":{"rendered":"<p>Because of their relative sizes and nearness to the earth, the sun and moon are not merely seen as points of light but as spheres with sizeable diameters.\u00a0 Therefore, in order to take a sextant altitude, the observer needs to measure the angle between the horizon and their upper or lower rims.<\/p>\n<p>This angle then needs to be corrected by either adding or subtracting their semi-diameters.\u00a0 The point on the rim of the sun closest to the horizon is referred to as the sun\u2019s <strong>lower limb <\/strong>and is denoted by either <strong>LL<\/strong> or <strong>O.<\/strong>The point on the rim furtherest from the horizon is referred to as the sun\u2019s upper limb and is denoted by either UL or O.\u00a0 If the sun\u2019s lower limb is used then the semi-diameter correction is added to the apparent altitude.\u00a0 If the upper limb is taken then it is subtracted.<\/p>\n<div id=\"attachment_91\" style=\"width: 910px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-91\" class=\"size-full wp-image-91\" src=\"https:\/\/maritimesa.org\/nautical-science-grade-11\/wp-content\/uploads\/sites\/6\/2020\/10\/11.1.5.9_fig_1.jpg\" alt=\"\" width=\"900\" height=\"720\" srcset=\"https:\/\/maritimesa.org\/nautical-science-grade-11\/wp-content\/uploads\/sites\/6\/2020\/10\/11.1.5.9_fig_1.jpg 900w, https:\/\/maritimesa.org\/nautical-science-grade-11\/wp-content\/uploads\/sites\/6\/2020\/10\/11.1.5.9_fig_1-300x240.jpg 300w, https:\/\/maritimesa.org\/nautical-science-grade-11\/wp-content\/uploads\/sites\/6\/2020\/10\/11.1.5.9_fig_1-768x614.jpg 768w, https:\/\/maritimesa.org\/nautical-science-grade-11\/wp-content\/uploads\/sites\/6\/2020\/10\/11.1.5.9_fig_1-183x146.jpg 183w, https:\/\/maritimesa.org\/nautical-science-grade-11\/wp-content\/uploads\/sites\/6\/2020\/10\/11.1.5.9_fig_1-50x40.jpg 50w, https:\/\/maritimesa.org\/nautical-science-grade-11\/wp-content\/uploads\/sites\/6\/2020\/10\/11.1.5.9_fig_1-94x75.jpg 94w\" sizes=\"(max-width: 900px) 100vw, 900px\" \/><p id=\"caption-attachment-91\" class=\"wp-caption-text\">Semi-diameter correction.<\/p><\/div>\n<p>&nbsp;<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Because of their relative sizes and nearness to the earth, the sun and moon are not merely seen as points of light but as spheres with sizeable diameters.\u00a0 Therefore, in order to take a sextant altitude, the observer needs to measure the angle between the horizon and their upper or [&hellip;]<\/p>\n","protected":false},"author":6,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[4,41,50],"tags":[],"class_list":["post-336","post","type-post","status-publish","format-standard","hentry","category-11-1-navigation","category-11-1-5-altitude-correction","category-11-1-5-9-correction-for-sem-diameter"],"_links":{"self":[{"href":"https:\/\/maritimesa.org\/nautical-science-grade-11\/wp-json\/wp\/v2\/posts\/336"}],"collection":[{"href":"https:\/\/maritimesa.org\/nautical-science-grade-11\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/maritimesa.org\/nautical-science-grade-11\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/maritimesa.org\/nautical-science-grade-11\/wp-json\/wp\/v2\/users\/6"}],"replies":[{"embeddable":true,"href":"https:\/\/maritimesa.org\/nautical-science-grade-11\/wp-json\/wp\/v2\/comments?post=336"}],"version-history":[{"count":1,"href":"https:\/\/maritimesa.org\/nautical-science-grade-11\/wp-json\/wp\/v2\/posts\/336\/revisions"}],"predecessor-version":[{"id":337,"href":"https:\/\/maritimesa.org\/nautical-science-grade-11\/wp-json\/wp\/v2\/posts\/336\/revisions\/337"}],"wp:attachment":[{"href":"https:\/\/maritimesa.org\/nautical-science-grade-11\/wp-json\/wp\/v2\/media?parent=336"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/maritimesa.org\/nautical-science-grade-11\/wp-json\/wp\/v2\/categories?post=336"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/maritimesa.org\/nautical-science-grade-11\/wp-json\/wp\/v2\/tags?post=336"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}