{"id":10929,"date":"2015-10-31T21:28:33","date_gmt":"2015-10-31T18:28:33","guid":{"rendered":"http:\/\/www.learning-mind.com\/?p=10929"},"modified":"2015-10-31T21:28:33","modified_gmt":"2015-10-31T18:28:33","slug":"motions-of-the-earth","status":"publish","type":"post","link":"https:\/\/www.learning-mind.com\/motions-of-the-earth\/","title":{"rendered":"5 Motions of the Earth You Didn&#8217;t Know Existed"},"content":{"rendered":"<p>We have learned from our early school time that <strong>the Earth has two motions<\/strong>: revolution around the Sun that takes 365 days 5 hours and 48 minutes (tropical year) and the Earth\u2019s rotation around its own axis that takes 23 hours 56 minutes and 4 seconds (sidereal day), 24 hours (solar day).<\/p>\n<p>However, <strong>Earth has other motions that are not well-known to the public<\/strong>. In this article, we intend to have a glimpse on some of these motions of the planet that we live on.<\/p>\n<h2>The motions of the Earth<\/h2>\n<p>Some of the additional motions of the Earth that have been discovered until now are the following:<\/p>\n<ul>\n<li>Precessional or wobbling motion of the Earth\u2019s axis<\/li>\n<li>Ellipticity change of the Earth\u2019s orbit around the Sun (change of eccentricity)<\/li>\n<li>Tilt change of the Earth\u2019s rotation axis<\/li>\n<li>Perihelion change of the Earth\u2019s orbit around the Sun<\/li>\n<li>Change in the orbital inclination of the Earth<\/li>\n<\/ul>\n<p>In this article, we are going to take a closer look at these motions in more detail.<\/p>\n<h3>1. The precessional motion of the Earth\u2019s axis<\/h3>\n<p><img decoding=\"async\" class=\"alignnone size-full wp-image-10938\" src=\"https:\/\/www.learning-mind.com\/wp-content\/uploads\/2015\/10\/motions-of-the-earth-precession.png\" alt=\"motions of the earth precession\" width=\"316\" height=\"140\" srcset=\"https:\/\/www.learning-mind.com\/wp-content\/uploads\/2015\/10\/motions-of-the-earth-precession.png 316w, https:\/\/www.learning-mind.com\/wp-content\/uploads\/2015\/10\/motions-of-the-earth-precession-300x133.png 300w\" sizes=\"(max-width: 316px) 100vw, 316px\" \/><\/p>\n<p>This motion is very similar to that of a spinning top in the <a href=\"https:\/\/www.learning-mind.com\/earths-magnetic-field-mystery\/\" target=\"_blank\" rel=\"noopener noreferrer\">Earth\u2019s gravitational field<\/a>. Besides its rotation around its own axis, the top\u2019s axis also has a rotation around the vertical axis with a fixed frequency. This is called the <strong>precessional or wobbling motion of the top.<\/strong><\/p>\n<p>The same rule applies to Earth. The Earth is not precisely a sphere and owing to its rotation and the fact that it is not completely rigid, its shape has become more <strong>an oblate ellipsoid<\/strong> instead of a complete sphere. Indeed, the equatorial diameter of the Earth is 42 kilometers larger than the polar diameter.<\/p>\n<p>As a result, due to the combined tidal forces of the Sun and the moon on the Earth\u2019s equatorial bulge, and its inclined axis of rotation relative to its orbital plane, there is a periodic motion of the Earth\u2019s axis with a period of about 23,000 years.<\/p>\n<p><strong>This has an interesting observable consequence.<\/strong> Although this motion is too slow to be discovered during our lifetime, yet, it is observable over long periods of time. About 5,000 years ago, the pole star was another star called <em><strong>Thuban (\u03b1 Draconis)<\/strong> <\/em>and not the present pole star (Polaris) that we see at nights.<\/p>\n<h3>2. Tilt change of the Earth\u2019s rotation axis<\/h3>\n<p><img fetchpriority=\"high\" decoding=\"async\" class=\"alignnone size-full wp-image-10939\" src=\"https:\/\/www.learning-mind.com\/wp-content\/uploads\/2015\/10\/motions-of-the-earth-rotation-axis.jpg\" alt=\"motions of the earth rotation axis\" width=\"650\" height=\"165\" srcset=\"https:\/\/www.learning-mind.com\/wp-content\/uploads\/2015\/10\/motions-of-the-earth-rotation-axis.jpg 650w, https:\/\/www.learning-mind.com\/wp-content\/uploads\/2015\/10\/motions-of-the-earth-rotation-axis-300x76.jpg 300w\" sizes=\"(max-width: 650px) 100vw, 650px\" \/><\/p>\n<p>The current angle of inclination that the Earth\u2019s axis of rotation has in relation to its plane of orbit around the Sun is 23.5\u2070. But careful observations by astronomers have made it clear that <strong>this angle is changing periodically with a period of 41,000 years<\/strong> from about 24.5\u2070 to 22.5\u2070.<\/p>\n<p>This motion is primarily due to the gravitational attraction of the Earth by the Sun and the deviances of the Earth\u2019s shape from a sphere. Interestingly, it has been found that this movement combined with the precessional movement of the Earth\u2019s axis of rotation has been <strong>the major cause of the Earth\u2019s periodic ice ages.<\/strong><strong>\u00a0<\/strong><\/p>\n<h3>3. Ellipticity (eccentricity) change of the Earth\u2019s orbit around the Sun (change of eccentricity or stretch)<\/h3>\n<p><img decoding=\"async\" class=\"alignnone wp-image-10940 size-full\" src=\"https:\/\/www.learning-mind.com\/wp-content\/uploads\/2015\/10\/motions-of-the-earth-eccentricity.jpg\" alt=\"motions of the earth eccentricity\" width=\"350\" height=\"311\" srcset=\"https:\/\/www.learning-mind.com\/wp-content\/uploads\/2015\/10\/motions-of-the-earth-eccentricity.jpg 350w, https:\/\/www.learning-mind.com\/wp-content\/uploads\/2015\/10\/motions-of-the-earth-eccentricity-300x267.jpg 300w\" sizes=\"(max-width: 350px) 100vw, 350px\" \/><\/p>\n<p>The Earth revolves around the Sun with a period of about 365 days. The shape of the Earth\u2019s orbit around the Sun is an ellipse with the Sun at its center. This shape indeed is not static and the ellipticity of this orbit changes over time from a complete circle to an ellipse and back. The period of this motion is not constant and it ranges from 100,000 to 120,000 years.<\/p>\n<h3>4. Perihelion change of the Earth\u2019s orbit around the Sun<\/h3>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-10941\" src=\"https:\/\/www.learning-mind.com\/wp-content\/uploads\/2015\/10\/motions-of-the-earth-perihelion.jpg\" alt=\"motions of the earth perihelion\" width=\"264\" height=\"232\" \/><\/p>\n<p>This motion is mainly due to the gravitational forces of other planets on the Earth. It leads to a regular change of the direction that the elliptical orbit of the Earth points to.<\/p>\n<h3>5. Change in the orbital inclination of the Earth<\/h3>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-10942\" src=\"https:\/\/www.learning-mind.com\/wp-content\/uploads\/2015\/10\/motions-of-the-earth-inclination.png\" alt=\"motions of the earth inclination\" width=\"225\" height=\"225\" srcset=\"https:\/\/www.learning-mind.com\/wp-content\/uploads\/2015\/10\/motions-of-the-earth-inclination.png 225w, https:\/\/www.learning-mind.com\/wp-content\/uploads\/2015\/10\/motions-of-the-earth-inclination-150x150.png 150w\" sizes=\"(max-width: 225px) 100vw, 225px\" \/><\/p>\n<p>It has been discovered that <strong>the Earth\u2019s plane of the orbit is not constant in time; rather, its inclination changes relative to the orbit or other planets<\/strong>. The average period of this motion is about 100,000 years. During this period, the angle of inclination changes from 2.5\u2070 to -2.5\u2070.<\/p>\n<h3>Conclusion<\/h3>\n<p>Although the above-mentioned motions of the Earth seem to be slight as compared to its two major motions; nevertheless, studies have proven that these periodic motions have significant long-term effects. Some examples of these efffects include the periodic <a href=\"https:\/\/www.learning-mind.com\/history-of-civilization-climate-change\/\" target=\"_blank\" rel=\"noopener noreferrer\">climate changes<\/a> on the Earth.<\/p>\n<p>In 1941, Serbian astronomer <strong>Milutin Milankovitch<\/strong> managed to prove that <strong>the tilt change of the Earth\u2019s axis of rotation, combined with its precessional movement, has led to many ice ages on the Earth<\/strong>.<\/p>\n<p>Later studies confirmed his findings and now it is believed that from three to one million years ago, the period of ice ages was 40,000 years with an abrupt change from 20,000 years prior to that.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-10943\" src=\"https:\/\/www.learning-mind.com\/wp-content\/uploads\/2015\/10\/motions-of-the-earth-milaknkovitch-cycles.png\" alt=\"motions of the earth milaknkovitch cycles\" width=\"394\" height=\"151\" srcset=\"https:\/\/www.learning-mind.com\/wp-content\/uploads\/2015\/10\/motions-of-the-earth-milaknkovitch-cycles.png 394w, https:\/\/www.learning-mind.com\/wp-content\/uploads\/2015\/10\/motions-of-the-earth-milaknkovitch-cycles-300x115.png 300w\" sizes=\"(max-width: 394px) 100vw, 394px\" \/><\/p>\n<p>We do not feel the motions of the Earth because we move with it and their effect cannot be sensed in our normal life. But they are real, just not fully understood yet.<\/p>\n<p><strong>References:<\/strong><\/p>\n<ul>\n<li><a href=\"https:\/\/spaceplace.nasa.gov\/seasons\/en\/\" target=\"_blank\" rel=\"noopener noreferrer nofollow\">What causes the seasons<\/a><\/li>\n<li>Principles of Astronomy by Dr. Jamie Love<\/li>\n<li><a href=\"http:\/\/www.eso.org\/public\/outreach\/eduoff\/aol\/\" target=\"_blank\" rel=\"noopener noreferrer nofollow\">Three motions of the Earth<\/a><\/li>\n<\/ul>\n","protected":false},"excerpt":{"rendered":"<p>We have learned from our early school time that the Earth has two motions: revolution around the Sun that takes 365 days 5 hours and 48 minutes (tropical year) and the Earth\u2019s rotation around its own axis that takes 23 hours 56 minutes and 4 seconds (sidereal day), 24 hours (solar day). However, Earth has [&hellip;]<\/p>\n","protected":false},"author":18,"featured_media":10937,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"ocean_post_layout":"","ocean_both_sidebars_style":"","ocean_both_sidebars_content_width":0,"ocean_both_sidebars_sidebars_width":0,"ocean_sidebar":"","ocean_second_sidebar":"","ocean_disable_margins":"enable","ocean_add_body_class":"","ocean_shortcode_before_top_bar":"","ocean_shortcode_after_top_bar":"","ocean_shortcode_before_header":"","ocean_shortcode_after_header":"","ocean_has_shortcode":"","ocean_shortcode_after_title":"","ocean_shortcode_before_footer_widgets":"","ocean_shortcode_after_footer_widgets":"","ocean_shortcode_before_footer_bottom":"","ocean_shortcode_after_footer_bottom":"","ocean_display_top_bar":"default","ocean_display_header":"default","ocean_header_style":"","ocean_center_header_left_menu":"","ocean_custom_header_template":"","ocean_custom_logo":0,"ocean_custom_retina_logo":0,"ocean_custom_logo_max_width":0,"ocean_custom_logo_tablet_max_width":0,"ocean_custom_logo_mobile_max_width":0,"ocean_custom_logo_max_height":0,"ocean_custom_logo_tablet_max_height":0,"ocean_custom_logo_mobile_max_height":0,"ocean_header_custom_menu":"","ocean_menu_typo_font_family":"","ocean_menu_typo_font_subset":"","ocean_menu_typo_font_size":0,"ocean_menu_typo_font_size_tablet":0,"ocean_menu_typo_font_size_mobile":0,"ocean_menu_typo_font_size_unit":"px","ocean_menu_typo_font_weight":"","ocean_menu_typo_font_weight_tablet":"","ocean_menu_typo_font_weight_mobile":"","ocean_menu_typo_transform":"","ocean_menu_typo_transform_tablet":"","ocean_menu_typo_transform_mobile":"","ocean_menu_typo_line_height":0,"ocean_menu_typo_line_height_tablet":0,"ocean_menu_typo_line_height_mobile":0,"ocean_menu_typo_line_height_unit":"","ocean_menu_typo_spacing":0,"ocean_menu_typo_spacing_tablet":0,"ocean_menu_typo_spacing_mobile":0,"ocean_menu_typo_spacing_unit":"","ocean_menu_link_color":"","ocean_menu_link_color_hover":"","ocean_menu_link_color_active":"","ocean_menu_link_background":"","ocean_menu_link_hover_background":"","ocean_menu_link_active_background":"","ocean_menu_social_links_bg":"","ocean_menu_social_hover_links_bg":"","ocean_menu_social_links_color":"","ocean_menu_social_hover_links_color":"","ocean_disable_title":"default","ocean_disable_heading":"default","ocean_post_title":"","ocean_post_subheading":"","ocean_post_title_style":"","ocean_post_title_background_color":"","ocean_post_title_background":0,"ocean_post_title_bg_image_position":"","ocean_post_title_bg_image_attachment":"","ocean_post_title_bg_image_repeat":"","ocean_post_title_bg_image_size":"","ocean_post_title_height":0,"ocean_post_title_bg_overlay":0.5,"ocean_post_title_bg_overlay_color":"","ocean_disable_breadcrumbs":"default","ocean_breadcrumbs_color":"","ocean_breadcrumbs_separator_color":"","ocean_breadcrumbs_links_color":"","ocean_breadcrumbs_links_hover_color":"","ocean_display_footer_widgets":"default","ocean_display_footer_bottom":"default","ocean_custom_footer_template":"","ocean_post_oembed":"","ocean_post_self_hosted_media":"","ocean_post_video_embed":"","ocean_link_format":"","ocean_link_format_target":"self","ocean_quote_format":"","ocean_quote_format_link":"post","ocean_gallery_link_images":"on","ocean_gallery_id":[],"footnotes":""},"categories":[31,22],"tags":[140,153],"_links":{"self":[{"href":"https:\/\/www.learning-mind.com\/wp-json\/wp\/v2\/posts\/10929"}],"collection":[{"href":"https:\/\/www.learning-mind.com\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.learning-mind.com\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.learning-mind.com\/wp-json\/wp\/v2\/users\/18"}],"replies":[{"embeddable":true,"href":"https:\/\/www.learning-mind.com\/wp-json\/wp\/v2\/comments?post=10929"}],"version-history":[{"count":0,"href":"https:\/\/www.learning-mind.com\/wp-json\/wp\/v2\/posts\/10929\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.learning-mind.com\/wp-json\/wp\/v2\/media\/10937"}],"wp:attachment":[{"href":"https:\/\/www.learning-mind.com\/wp-json\/wp\/v2\/media?parent=10929"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.learning-mind.com\/wp-json\/wp\/v2\/categories?post=10929"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.learning-mind.com\/wp-json\/wp\/v2\/tags?post=10929"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}