{"id":609,"date":"2022-03-02T17:51:59","date_gmt":"2022-03-02T17:51:59","guid":{"rendered":"https:\/\/pressbooks.ccconline.org\/astronomy\/?post_type=chapter&#038;p=609"},"modified":"2022-04-29T18:17:35","modified_gmt":"2022-04-29T18:17:35","slug":"20-1-the-interstellar-medium","status":"publish","type":"chapter","link":"https:\/\/pressbooks.ccconline.org\/astronomy\/chapter\/20-1-the-interstellar-medium\/","title":{"raw":"20.1 The Interstellar Medium","rendered":"20.1 The Interstellar Medium"},"content":{"raw":"<div class=\"textbox textbox--learning-objectives\"><header class=\"textbox__header\">\r\n<h3 class=\"textbox__title\">Learning Objectives<\/h3>\r\n<\/header>\r\n<div class=\"textbox__content\">\r\n<p id=\"fs-id1168583245848\">By the end of this section, you will be able to:<\/p>\r\n\r\n<ul id=\"fs-id1168048316626\">\r\n \t<li>Explain how much interstellar matter there is in the Milky Way, and what its typical density is<\/li>\r\n \t<li>Describe how the interstellar medium is divided into gaseous and solid components<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n<p id=\"fs-id1168048507175\">Astronomers refer to all the material between stars as\u00a0<em data-effect=\"italics\">interstellar<\/em>\u00a0matter; the entire collection of interstellar matter is called the\u00a0<span id=\"term1070\" data-type=\"term\">interstellar medium (ISM)<\/span>. Some interstellar material is concentrated into giant clouds, each of which is known as a\u00a0<span id=\"term1071\" data-type=\"term\">nebula<\/span>\u00a0(plural \u201cnebulae,\u201d Latin for \u201cclouds\u201d). The best-known nebulae are the ones that we can see glowing or reflecting visible light; there are many pictures of these in this chapter.<\/p>\r\n<p id=\"fs-id1168048343506\">Interstellar clouds do not last for the lifetime of the universe. Instead, they are like clouds on Earth, constantly shifting, merging with each other, growing, or dispersing. Some become dense and massive enough to collapse under their own gravity, forming new stars. When stars die, they, in turn, eject some of their material into interstellar space. This material can then form new clouds and begin the cycle over again.<\/p>\r\n<p id=\"fs-id1168048740700\">About 99% of the material between the stars is in the form of a\u00a0<em data-effect=\"italics\">gas<\/em>\u2014that is, it consists of individual atoms or molecules. The most abundant elements in this gas are hydrogen and helium (which we saw are also the most abundant elements in the stars), but the gas also includes other elements. Some of the gas is in the form of molecules\u2014combinations of atoms. The remaining 1% of the interstellar material is solid\u2014frozen particles consisting of many atoms and molecules that are called\u00a0<em data-effect=\"italics\">interstellar grains<\/em>\u00a0or\u00a0<span id=\"term1072\" data-type=\"term\">interstellar dust<\/span>\u00a0(Figure 20.2). A typical dust grain consists of a core of rocklike material (silicates) or graphite surrounded by a mantle of ices; water, methane, and ammonia are probably the most abundant ices.<\/p>\r\n\r\n<div id=\"OSC_Astro_20_01_Interster\" class=\"os-figure\">\r\n<figure data-id=\"OSC_Astro_20_01_Interster\">\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"487\"]<img id=\"2\" src=\"https:\/\/openstax.org\/apps\/archive\/20220118.185250\/resources\/48b3e2b2da901c5fda2993e10d43c200b0b73971\" alt=\"Various Types of Interstellar Matter. Antares, the brightest star in the constellation Scorpio, is at lower left in this wide-field image. It is surrounded by reddish nebulosity. To the right of Antares is the globular cluster M4. At center left a bright star is surrounded by the blue glow of a reflection nebula, and at center right another bright star is surrounded by red nebulosity. Above these two stars a dark nebula snakes its way across the image, blocking the light from behind. Finally, at top center, a bright star is surrounded by a large area of blue reflection nebulosity, criss-crossed by dark dust lanes.\" width=\"487\" height=\"613\" data-media-type=\"image\/jpeg\" \/> <strong>Figure\u00a020.2\u00a0<\/strong>Various Types of Interstellar Matter.\u00a0The reddish nebulae in this spectacular photograph glow with light emitted by hydrogen atoms. The darkest areas are clouds of dust that block the light from stars behind them. The upper part of the picture is filled with the bluish glow of light reflected from hot stars embedded in the outskirts of a huge, cool cloud of dust and gas. The cool supergiant star Antares can be seen as a big, reddish patch in the lower-left part of the picture. The star is shedding some of its outer atmosphere and is surrounded by a cloud of its own making that reflects the red light of the star. The red nebula in the middle right partially surrounds the star Sigma Scorpii. (To the right of Antares, you can see M4, a much more distant cluster of extremely old stars.) (credit: modification of work by ESO\/Digitized Sky Survey 2)[\/caption]<\/figure>\r\n<\/div>\r\n<p id=\"fs-id1168046107944\">If all the interstellar gas within the Galaxy were spread out smoothly, there would be only about one atom of gas per [latex]{\\rm{c}}{{\\rm{m}}^3}[\/latex]\u00a0in interstellar space. (In contrast, the air in the room where you are reading this book has roughly [latex]{10^{19}}[\/latex]\u00a0atoms per [latex]{\\rm{c}}{{\\rm{m}}^3}[\/latex].) The dust grains are even scarcer. A [latex]{\\rm{k}}{{\\rm{m}}^3}[\/latex]\u00a0of space would contain only a few hundred to a few thousand tiny grains, each typically less than one ten-thousandth of a millimeter in diameter. These numbers are just averages, however, because the gas and dust are distributed in a patchy and irregular way, much as water vapor in Earth\u2019s atmosphere is often concentrated into clouds.<\/p>\r\n<p id=\"fs-id1168048515122\">In some interstellar clouds, the density of gas and dust may exceed the average by as much as a thousand times or more, but even this density is more nearly a vacuum than any we can make on Earth. To show what we mean, let\u2019s imagine a vertical tube of air reaching from the ground to the top of Earth\u2019s atmosphere with a cross-section of 1 square meter. Now let us extend the same-size tube from the top of the atmosphere all the way to the edge of the observable universe\u2014over 10 billion light-years away. Long though it is, the second tube would still contain fewer atoms than the one in our planet\u2019s atmosphere.<\/p>\r\n<p id=\"fs-id1168048488131\">While the\u00a0<em data-effect=\"italics\">density<\/em>\u00a0of interstellar matter is very low, the volume of space in which such matter is found is huge, and so its\u00a0<em data-effect=\"italics\">total<\/em>\u00a0<em data-effect=\"italics\">mass<\/em>\u00a0is substantial. To see why, we must bear in mind that stars occupy only a tiny fraction of the volume of the Milky Way Galaxy. For example, it takes light only about four seconds to travel a distance equal to the diameter of the Sun, but more than four\u00a0<em data-effect=\"italics\">years<\/em>\u00a0to travel from the Sun to the nearest star. Even though the spaces among the stars are sparsely populated, there\u2019s a lot of space out there!<\/p>\r\n<p id=\"fs-id1168048517727\">Astronomers estimate that the total mass of gas and dust in the\u00a0<span id=\"term1073\" class=\"no-emphasis\" data-type=\"term\">Milky Way Galaxy<\/span>\u00a0is equal to about 15% of the mass contained in stars. This means that the mass of the interstellar matter in our Galaxy amounts to about 10 billion times the mass of the Sun. There is plenty of raw material in the Galaxy to make generations of new stars and planets (and perhaps even astronomy students).<\/p>\r\n\r\n<div class=\"textbox textbox--key-takeaways\"><header class=\"textbox__header\">\r\n<h3 class=\"textbox__title\">Astronomy Basics<\/h3>\r\n<\/header>\r\n<div class=\"textbox__content\">\r\n<h4 id=\"4\" class=\"os-subtitle\" data-type=\"title\"><span class=\"os-subtitle-label\">Naming the Nebulae<\/span><\/h4>\r\n<p id=\"fs-id1168048402169\">As you look at the captions for some of the spectacular photographs in this chapter and\u00a0The Birth of Stars and the Discovery of Planets outside the Solar System, you will notice the variety of names given to the\u00a0<span id=\"term1076\" class=\"no-emphasis\" data-type=\"term\">nebula<\/span>e. A few, which in small telescopes look like something recognizable, are sometimes named after the creatures or objects they resemble. Examples include the Crab, Tarantula, and Keyhole Nebulae. But most have only numbers that are entries in a catalog of astronomical objects.<\/p>\r\n<p id=\"fs-id1168048515852\">Perhaps the best-known catalog of nebulae (as well as star clusters and galaxies) was compiled by the French astronomer Charles\u00a0<span id=\"term1077\" class=\"no-emphasis\" data-type=\"term\">Messier<\/span>\u00a0(1730\u20131817). Messier\u2019s passion was discovering\u00a0<span id=\"term1078\" class=\"no-emphasis\" data-type=\"term\">comets<\/span>, and his devotion to this cause earned him the nickname \u201cThe Comet Ferret\u201d from King Louis XV. When comets are first seen coming toward the Sun, they look like little fuzzy patches of light; in small telescopes, they are easy to confuse with nebulae or with groupings of many stars so far away that their light is all blended together. Time and again, Messier\u2019s heart leapt as he thought he had discovered one of his treasured comets, only to find that he had \u201cmerely\u201d observed a nebula or cluster.<\/p>\r\n<p id=\"fs-id1168048512167\">In frustration, Messier set out to catalog the position and appearance of over 100 objects that could be mistaken for comets. For him, this list was merely a tool in the far more important work of comet hunting. He would be very surprised if he returned today to discover that no one recalls his comets anymore, but his catalog of \u201cfuzzy things that are not comets\u201d is still widely used. When\u00a0Figure 20.2\u00a0refers to M4, it denotes the fourth entry in Messier\u2019s list. Visit\u00a0<a href=\"https:\/\/www.nasa.gov\/content\/goddard\/hubble-s-messier-catalog\" target=\"_blank\" rel=\"noopener nofollow noreferrer\">https:\/\/www.nasa.gov\/content\/goddard\/hubble-s-messier-catalog<\/a>\u00a0for a gallery of M objects as photographed with the Hubble Space Telescope.<\/p>\r\n<p id=\"fs-id1168048345820\">A far more extensive listing was compiled under the title of the\u00a0<em data-effect=\"italics\">New General Catalog<\/em>\u00a0(<em data-effect=\"italics\">NGC<\/em>)\u00a0<em data-effect=\"italics\">of Nebulae and Star Clusters<\/em>\u00a0in 1888 by John\u00a0<span id=\"term1079\" class=\"no-emphasis\" data-type=\"term\">Dreyer<\/span>, working at the observatory in Armagh, Ireland. He based his compilation on the work of William\u00a0<span id=\"term1080\" class=\"no-emphasis\" data-type=\"term\">Herschel<\/span>\u00a0and his son John, plus many other observers who followed them. With the addition of two further listings (called the\u00a0<em data-effect=\"italics\">Index Catalogs<\/em>), Dreyer\u2019s compilation eventually included 13,000 objects. Astronomers today still use his NGC numbers when referring to most nebulae and star groups.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n<div class=\"textbox\">This book was adapted from the following: Fraknoi, A., Morrison, D., &amp; Wolff, S. C. (2016). 20.1 The Interstellar Medium In <i>Astronomy<\/i>. OpenStax. https:\/\/openstax.org\/books\/astronomy\/pages\/20-1-the-interstellar-medium under a <a href=\"http:\/\/creativecommons.org\/licenses\/by\/4.0\/\" target=\"_blank\" rel=\"noopener noreferrer\">Creative Commons Attribution License 4.0<\/a><\/div>\r\n<div>Access the entire book for free at\u00a0<a href=\"https:\/\/openstax.org\/books\/astronomy\/pages\/1-introduction\">https:\/\/openstax.org\/books\/astronomy\/pages\/1-introduction<\/a><\/div>","rendered":"<div class=\"textbox textbox--learning-objectives\">\n<header class=\"textbox__header\">\n<h3 class=\"textbox__title\">Learning Objectives<\/h3>\n<\/header>\n<div class=\"textbox__content\">\n<p id=\"fs-id1168583245848\">By the end of this section, you will be able to:<\/p>\n<ul id=\"fs-id1168048316626\">\n<li>Explain how much interstellar matter there is in the Milky Way, and what its typical density is<\/li>\n<li>Describe how the interstellar medium is divided into gaseous and solid components<\/li>\n<\/ul>\n<\/div>\n<\/div>\n<p id=\"fs-id1168048507175\">Astronomers refer to all the material between stars as\u00a0<em data-effect=\"italics\">interstellar<\/em>\u00a0matter; the entire collection of interstellar matter is called the\u00a0<span id=\"term1070\" data-type=\"term\">interstellar medium (ISM)<\/span>. Some interstellar material is concentrated into giant clouds, each of which is known as a\u00a0<span id=\"term1071\" data-type=\"term\">nebula<\/span>\u00a0(plural \u201cnebulae,\u201d Latin for \u201cclouds\u201d). The best-known nebulae are the ones that we can see glowing or reflecting visible light; there are many pictures of these in this chapter.<\/p>\n<p id=\"fs-id1168048343506\">Interstellar clouds do not last for the lifetime of the universe. Instead, they are like clouds on Earth, constantly shifting, merging with each other, growing, or dispersing. Some become dense and massive enough to collapse under their own gravity, forming new stars. When stars die, they, in turn, eject some of their material into interstellar space. This material can then form new clouds and begin the cycle over again.<\/p>\n<p id=\"fs-id1168048740700\">About 99% of the material between the stars is in the form of a\u00a0<em data-effect=\"italics\">gas<\/em>\u2014that is, it consists of individual atoms or molecules. The most abundant elements in this gas are hydrogen and helium (which we saw are also the most abundant elements in the stars), but the gas also includes other elements. Some of the gas is in the form of molecules\u2014combinations of atoms. The remaining 1% of the interstellar material is solid\u2014frozen particles consisting of many atoms and molecules that are called\u00a0<em data-effect=\"italics\">interstellar grains<\/em>\u00a0or\u00a0<span id=\"term1072\" data-type=\"term\">interstellar dust<\/span>\u00a0(Figure 20.2). A typical dust grain consists of a core of rocklike material (silicates) or graphite surrounded by a mantle of ices; water, methane, and ammonia are probably the most abundant ices.<\/p>\n<div id=\"OSC_Astro_20_01_Interster\" class=\"os-figure\">\n<figure data-id=\"OSC_Astro_20_01_Interster\">\n<figure style=\"width: 487px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" id=\"2\" src=\"https:\/\/openstax.org\/apps\/archive\/20220118.185250\/resources\/48b3e2b2da901c5fda2993e10d43c200b0b73971\" alt=\"Various Types of Interstellar Matter. Antares, the brightest star in the constellation Scorpio, is at lower left in this wide-field image. It is surrounded by reddish nebulosity. To the right of Antares is the globular cluster M4. At center left a bright star is surrounded by the blue glow of a reflection nebula, and at center right another bright star is surrounded by red nebulosity. Above these two stars a dark nebula snakes its way across the image, blocking the light from behind. Finally, at top center, a bright star is surrounded by a large area of blue reflection nebulosity, criss-crossed by dark dust lanes.\" width=\"487\" height=\"613\" data-media-type=\"image\/jpeg\" \/><figcaption class=\"wp-caption-text\"><strong>Figure\u00a020.2\u00a0<\/strong>Various Types of Interstellar Matter.\u00a0The reddish nebulae in this spectacular photograph glow with light emitted by hydrogen atoms. The darkest areas are clouds of dust that block the light from stars behind them. The upper part of the picture is filled with the bluish glow of light reflected from hot stars embedded in the outskirts of a huge, cool cloud of dust and gas. The cool supergiant star Antares can be seen as a big, reddish patch in the lower-left part of the picture. The star is shedding some of its outer atmosphere and is surrounded by a cloud of its own making that reflects the red light of the star. The red nebula in the middle right partially surrounds the star Sigma Scorpii. (To the right of Antares, you can see M4, a much more distant cluster of extremely old stars.) (credit: modification of work by ESO\/Digitized Sky Survey 2)<\/figcaption><\/figure>\n<\/figure>\n<\/div>\n<p id=\"fs-id1168046107944\">If all the interstellar gas within the Galaxy were spread out smoothly, there would be only about one atom of gas per [latex]{\\rm{c}}{{\\rm{m}}^3}[\/latex]\u00a0in interstellar space. (In contrast, the air in the room where you are reading this book has roughly [latex]{10^{19}}[\/latex]\u00a0atoms per [latex]{\\rm{c}}{{\\rm{m}}^3}[\/latex].) The dust grains are even scarcer. A [latex]{\\rm{k}}{{\\rm{m}}^3}[\/latex]\u00a0of space would contain only a few hundred to a few thousand tiny grains, each typically less than one ten-thousandth of a millimeter in diameter. These numbers are just averages, however, because the gas and dust are distributed in a patchy and irregular way, much as water vapor in Earth\u2019s atmosphere is often concentrated into clouds.<\/p>\n<p id=\"fs-id1168048515122\">In some interstellar clouds, the density of gas and dust may exceed the average by as much as a thousand times or more, but even this density is more nearly a vacuum than any we can make on Earth. To show what we mean, let\u2019s imagine a vertical tube of air reaching from the ground to the top of Earth\u2019s atmosphere with a cross-section of 1 square meter. Now let us extend the same-size tube from the top of the atmosphere all the way to the edge of the observable universe\u2014over 10 billion light-years away. Long though it is, the second tube would still contain fewer atoms than the one in our planet\u2019s atmosphere.<\/p>\n<p id=\"fs-id1168048488131\">While the\u00a0<em data-effect=\"italics\">density<\/em>\u00a0of interstellar matter is very low, the volume of space in which such matter is found is huge, and so its\u00a0<em data-effect=\"italics\">total<\/em>\u00a0<em data-effect=\"italics\">mass<\/em>\u00a0is substantial. To see why, we must bear in mind that stars occupy only a tiny fraction of the volume of the Milky Way Galaxy. For example, it takes light only about four seconds to travel a distance equal to the diameter of the Sun, but more than four\u00a0<em data-effect=\"italics\">years<\/em>\u00a0to travel from the Sun to the nearest star. Even though the spaces among the stars are sparsely populated, there\u2019s a lot of space out there!<\/p>\n<p id=\"fs-id1168048517727\">Astronomers estimate that the total mass of gas and dust in the\u00a0<span id=\"term1073\" class=\"no-emphasis\" data-type=\"term\">Milky Way Galaxy<\/span>\u00a0is equal to about 15% of the mass contained in stars. This means that the mass of the interstellar matter in our Galaxy amounts to about 10 billion times the mass of the Sun. There is plenty of raw material in the Galaxy to make generations of new stars and planets (and perhaps even astronomy students).<\/p>\n<div class=\"textbox textbox--key-takeaways\">\n<header class=\"textbox__header\">\n<h3 class=\"textbox__title\">Astronomy Basics<\/h3>\n<\/header>\n<div class=\"textbox__content\">\n<h4 id=\"4\" class=\"os-subtitle\" data-type=\"title\"><span class=\"os-subtitle-label\">Naming the Nebulae<\/span><\/h4>\n<p id=\"fs-id1168048402169\">As you look at the captions for some of the spectacular photographs in this chapter and\u00a0The Birth of Stars and the Discovery of Planets outside the Solar System, you will notice the variety of names given to the\u00a0<span id=\"term1076\" class=\"no-emphasis\" data-type=\"term\">nebula<\/span>e. A few, which in small telescopes look like something recognizable, are sometimes named after the creatures or objects they resemble. Examples include the Crab, Tarantula, and Keyhole Nebulae. But most have only numbers that are entries in a catalog of astronomical objects.<\/p>\n<p id=\"fs-id1168048515852\">Perhaps the best-known catalog of nebulae (as well as star clusters and galaxies) was compiled by the French astronomer Charles\u00a0<span id=\"term1077\" class=\"no-emphasis\" data-type=\"term\">Messier<\/span>\u00a0(1730\u20131817). Messier\u2019s passion was discovering\u00a0<span id=\"term1078\" class=\"no-emphasis\" data-type=\"term\">comets<\/span>, and his devotion to this cause earned him the nickname \u201cThe Comet Ferret\u201d from King Louis XV. When comets are first seen coming toward the Sun, they look like little fuzzy patches of light; in small telescopes, they are easy to confuse with nebulae or with groupings of many stars so far away that their light is all blended together. Time and again, Messier\u2019s heart leapt as he thought he had discovered one of his treasured comets, only to find that he had \u201cmerely\u201d observed a nebula or cluster.<\/p>\n<p id=\"fs-id1168048512167\">In frustration, Messier set out to catalog the position and appearance of over 100 objects that could be mistaken for comets. For him, this list was merely a tool in the far more important work of comet hunting. He would be very surprised if he returned today to discover that no one recalls his comets anymore, but his catalog of \u201cfuzzy things that are not comets\u201d is still widely used. When\u00a0Figure 20.2\u00a0refers to M4, it denotes the fourth entry in Messier\u2019s list. Visit\u00a0<a href=\"https:\/\/www.nasa.gov\/content\/goddard\/hubble-s-messier-catalog\" target=\"_blank\" rel=\"noopener nofollow noreferrer\">https:\/\/www.nasa.gov\/content\/goddard\/hubble-s-messier-catalog<\/a>\u00a0for a gallery of M objects as photographed with the Hubble Space Telescope.<\/p>\n<p id=\"fs-id1168048345820\">A far more extensive listing was compiled under the title of the\u00a0<em data-effect=\"italics\">New General Catalog<\/em>\u00a0(<em data-effect=\"italics\">NGC<\/em>)\u00a0<em data-effect=\"italics\">of Nebulae and Star Clusters<\/em>\u00a0in 1888 by John\u00a0<span id=\"term1079\" class=\"no-emphasis\" data-type=\"term\">Dreyer<\/span>, working at the observatory in Armagh, Ireland. He based his compilation on the work of William\u00a0<span id=\"term1080\" class=\"no-emphasis\" data-type=\"term\">Herschel<\/span>\u00a0and his son John, plus many other observers who followed them. With the addition of two further listings (called the\u00a0<em data-effect=\"italics\">Index Catalogs<\/em>), Dreyer\u2019s compilation eventually included 13,000 objects. Astronomers today still use his NGC numbers when referring to most nebulae and star groups.<\/p>\n<\/div>\n<\/div>\n<div class=\"textbox\">This book was adapted from the following: Fraknoi, A., Morrison, D., &amp; Wolff, S. C. (2016). 20.1 The Interstellar Medium In <i>Astronomy<\/i>. OpenStax. https:\/\/openstax.org\/books\/astronomy\/pages\/20-1-the-interstellar-medium under a <a href=\"http:\/\/creativecommons.org\/licenses\/by\/4.0\/\" target=\"_blank\" rel=\"noopener noreferrer\">Creative Commons Attribution License 4.0<\/a><\/div>\n<div>Access the entire book for free at\u00a0<a href=\"https:\/\/openstax.org\/books\/astronomy\/pages\/1-introduction\">https:\/\/openstax.org\/books\/astronomy\/pages\/1-introduction<\/a><\/div>\n","protected":false},"author":33,"menu_order":11,"template":"","meta":{"pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[48],"contributor":[],"license":[],"class_list":["post-609","chapter","type-chapter","status-publish","hentry","chapter-type-numberless"],"part":607,"_links":{"self":[{"href":"https:\/\/pressbooks.ccconline.org\/astronomy\/wp-json\/pressbooks\/v2\/chapters\/609","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/pressbooks.ccconline.org\/astronomy\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/pressbooks.ccconline.org\/astronomy\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/pressbooks.ccconline.org\/astronomy\/wp-json\/wp\/v2\/users\/33"}],"version-history":[{"count":5,"href":"https:\/\/pressbooks.ccconline.org\/astronomy\/wp-json\/pressbooks\/v2\/chapters\/609\/revisions"}],"predecessor-version":[{"id":1060,"href":"https:\/\/pressbooks.ccconline.org\/astronomy\/wp-json\/pressbooks\/v2\/chapters\/609\/revisions\/1060"}],"part":[{"href":"https:\/\/pressbooks.ccconline.org\/astronomy\/wp-json\/pressbooks\/v2\/parts\/607"}],"metadata":[{"href":"https:\/\/pressbooks.ccconline.org\/astronomy\/wp-json\/pressbooks\/v2\/chapters\/609\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/pressbooks.ccconline.org\/astronomy\/wp-json\/wp\/v2\/media?parent=609"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/pressbooks.ccconline.org\/astronomy\/wp-json\/pressbooks\/v2\/chapter-type?post=609"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/pressbooks.ccconline.org\/astronomy\/wp-json\/wp\/v2\/contributor?post=609"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/pressbooks.ccconline.org\/astronomy\/wp-json\/wp\/v2\/license?post=609"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}