{"id":247,"date":"2022-02-11T16:29:42","date_gmt":"2022-02-11T16:29:42","guid":{"rendered":"https:\/\/pressbooks.ccconline.org\/astronomy\/?post_type=chapter&p=247"},"modified":"2022-04-22T17:03:54","modified_gmt":"2022-04-22T17:03:54","slug":"summary-2","status":"publish","type":"chapter","link":"https:\/\/pressbooks.ccconline.org\/astronomy\/chapter\/summary-2\/","title":{"raw":"Summary","rendered":"Summary"},"content":{"raw":"
\r\n

4.1<\/span>\u00a0<\/span>Earth and Sky<\/span><\/h3>\r\n

The terrestrial system of latitude and longitude makes use of the great circles called meridians. Longitude is arbitrarily set to 0\u00b0 at the Royal Observatory at Greenwich, England. An analogous celestial coordinate system is called right ascension (RA) and declination, with 0\u00b0 of declination starting at the vernal equinox. These coordinate systems help us locate any object on the celestial sphere. The Foucault pendulum is a way to demonstrate that Earth is turning.<\/p>\r\n\r\n<\/section>

\r\n

4.2<\/span>\u00a0<\/span>The Seasons<\/span><\/h3>\r\n

The familiar cycle of the seasons results from the 23.5\u00b0 tilt of Earth\u2019s axis of rotation. At the summer solstice, the Sun is higher in the sky and its rays strike Earth more directly. The Sun is in the sky for more than half of the day and can heat Earth longer. At the winter solstice, the Sun is low in the sky and its rays come in at more of an angle; in addition, it is up for fewer than 12 hours, so those rays have less time to heat. At the vernal and autumnal equinoxes, the Sun is on the celestial equator and we get about 12 hours of day and night. The seasons are different at different latitudes.<\/p>\r\n\r\n<\/section>

\r\n

4.3<\/span>\u00a0<\/span>Keeping Time<\/span><\/h3>\r\n

The basic unit of astronomical time is the day\u2014either the solar day (reckoned by the Sun) or the sidereal day (reckoned by the stars). Apparent solar time is based on the position of the Sun in the sky, and mean solar time is based on the average value of a solar day during the year. By international agreement, we define 24 time zones around the world, each with its own standard time. The convention of the International Date Line is necessary to reconcile times on different parts of Earth.<\/p>\r\n\r\n<\/section>

\r\n

4.4<\/span>\u00a0<\/span>The Calendar<\/span><\/h3>\r\n

The fundamental problem of the calendar is to reconcile the incommensurable lengths of the day, month, and year. Most modern calendars, beginning with the Roman (Julian) calendar of the first century BCE, neglect the problem of the month and concentrate on achieving the correct number of days in a year by using such conventions as the leap year. Today, most of the world has adopted the Gregorian calendar established in 1582 while finding ways to coexist with the older lunar calendars\u2019 system of months.<\/p>\r\n\r\n<\/section>

\r\n

4.5<\/span>\u00a0<\/span>Phases and Motions of the Moon<\/span><\/h3>\r\n

The Moon\u2019s monthly cycle of phases results from the changing angle of its illumination by the Sun. The full moon is visible in the sky only during the night; other phases are visible during the day as well. Because its period of revolution is the same as its period of rotation, the Moon always keeps the same face toward Earth.<\/p>\r\n\r\n<\/section>

\r\n

4.6<\/span>\u00a0<\/span>Ocean Tides and the Moon<\/span><\/h3>\r\n

The twice-daily ocean tides are primarily the result of the Moon\u2019s differential force on the material of Earth\u2019s crust and ocean. These tidal forces cause ocean water to flow into two tidal bulges on opposite sides of Earth; each day, Earth rotates through these bulges. Actual ocean tides are complicated by the additional effects of the Sun and by the shape of the coasts and ocean basins.<\/p>\r\n\r\n<\/section>

\r\n

4.7<\/span>\u00a0<\/span>Eclipses of the Sun and Moon<\/span><\/h3>\r\n

The Sun and Moon have nearly the same angular size (about [latex]1\/2^\\circ [\/latex]). A solar eclipse occurs when the Moon moves between the Sun and Earth, casting its shadow on a part of Earth\u2019s surface. If the eclipse is total, the light from the bright disk of the Sun is completely blocked, and the solar atmosphere (the corona) comes into view. Solar eclipses take place rarely in any one location, but they are among the most spectacular sights in nature. A lunar eclipse takes place when the Moon moves into Earth\u2019s shadow; it is visible (weather permitting) from the entire night hemisphere of Earth.<\/p>\r\n\r\n<\/section>\r\n

This book was adapted from the following: Fraknoi, A., Morrison, D., & Wolff, S. C. (2016). Summary. In Astronomy<\/i>. OpenStax. https:\/\/openstax.org\/books\/astronomy\/pages\/4-summary under a Creative Commons Attribution License 4.0<\/a><\/div>\r\n
Access the entire book for free at https:\/\/openstax.org\/books\/astronomy\/pages\/1-introduction<\/a><\/div>","rendered":"
\n

4.1<\/span>\u00a0<\/span>Earth and Sky<\/span><\/h3>\n

The terrestrial system of latitude and longitude makes use of the great circles called meridians. Longitude is arbitrarily set to 0\u00b0 at the Royal Observatory at Greenwich, England. An analogous celestial coordinate system is called right ascension (RA) and declination, with 0\u00b0 of declination starting at the vernal equinox. These coordinate systems help us locate any object on the celestial sphere. The Foucault pendulum is a way to demonstrate that Earth is turning.<\/p>\n<\/section>\n

\n

4.2<\/span>\u00a0<\/span>The Seasons<\/span><\/h3>\n

The familiar cycle of the seasons results from the 23.5\u00b0 tilt of Earth\u2019s axis of rotation. At the summer solstice, the Sun is higher in the sky and its rays strike Earth more directly. The Sun is in the sky for more than half of the day and can heat Earth longer. At the winter solstice, the Sun is low in the sky and its rays come in at more of an angle; in addition, it is up for fewer than 12 hours, so those rays have less time to heat. At the vernal and autumnal equinoxes, the Sun is on the celestial equator and we get about 12 hours of day and night. The seasons are different at different latitudes.<\/p>\n<\/section>\n

\n

4.3<\/span>\u00a0<\/span>Keeping Time<\/span><\/h3>\n

The basic unit of astronomical time is the day\u2014either the solar day (reckoned by the Sun) or the sidereal day (reckoned by the stars). Apparent solar time is based on the position of the Sun in the sky, and mean solar time is based on the average value of a solar day during the year. By international agreement, we define 24 time zones around the world, each with its own standard time. The convention of the International Date Line is necessary to reconcile times on different parts of Earth.<\/p>\n<\/section>\n

\n

4.4<\/span>\u00a0<\/span>The Calendar<\/span><\/h3>\n

The fundamental problem of the calendar is to reconcile the incommensurable lengths of the day, month, and year. Most modern calendars, beginning with the Roman (Julian) calendar of the first century BCE, neglect the problem of the month and concentrate on achieving the correct number of days in a year by using such conventions as the leap year. Today, most of the world has adopted the Gregorian calendar established in 1582 while finding ways to coexist with the older lunar calendars\u2019 system of months.<\/p>\n<\/section>\n

\n

4.5<\/span>\u00a0<\/span>Phases and Motions of the Moon<\/span><\/h3>\n

The Moon\u2019s monthly cycle of phases results from the changing angle of its illumination by the Sun. The full moon is visible in the sky only during the night; other phases are visible during the day as well. Because its period of revolution is the same as its period of rotation, the Moon always keeps the same face toward Earth.<\/p>\n<\/section>\n

\n

4.6<\/span>\u00a0<\/span>Ocean Tides and the Moon<\/span><\/h3>\n

The twice-daily ocean tides are primarily the result of the Moon\u2019s differential force on the material of Earth\u2019s crust and ocean. These tidal forces cause ocean water to flow into two tidal bulges on opposite sides of Earth; each day, Earth rotates through these bulges. Actual ocean tides are complicated by the additional effects of the Sun and by the shape of the coasts and ocean basins.<\/p>\n<\/section>\n

\n

4.7<\/span>\u00a0<\/span>Eclipses of the Sun and Moon<\/span><\/h3>\n

The Sun and Moon have nearly the same angular size (about [latex]1\/2^\\circ[\/latex]). A solar eclipse occurs when the Moon moves between the Sun and Earth, casting its shadow on a part of Earth\u2019s surface. If the eclipse is total, the light from the bright disk of the Sun is completely blocked, and the solar atmosphere (the corona) comes into view. Solar eclipses take place rarely in any one location, but they are among the most spectacular sights in nature. A lunar eclipse takes place when the Moon moves into Earth\u2019s shadow; it is visible (weather permitting) from the entire night hemisphere of Earth.<\/p>\n<\/section>\n

This book was adapted from the following: Fraknoi, A., Morrison, D., & Wolff, S. C. (2016). Summary. In Astronomy<\/i>. OpenStax. https:\/\/openstax.org\/books\/astronomy\/pages\/4-summary under a Creative Commons Attribution License 4.0<\/a><\/div>\n
Access the entire book for free at https:\/\/openstax.org\/books\/astronomy\/pages\/1-introduction<\/a><\/div>\n","protected":false},"author":33,"menu_order":9,"template":"","meta":{"pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[48],"contributor":[],"license":[],"class_list":["post-247","chapter","type-chapter","status-publish","hentry","chapter-type-numberless"],"part":222,"_links":{"self":[{"href":"https:\/\/pressbooks.ccconline.org\/astronomy\/wp-json\/pressbooks\/v2\/chapters\/247","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":4,"href":"https:\/\/pressbooks.ccconline.org\/astronomy\/wp-json\/pressbooks\/v2\/chapters\/247\/revisions"}],"predecessor-version":[{"id":795,"href":"https:\/\/pressbooks.ccconline.org\/astronomy\/wp-json\/pressbooks\/v2\/chapters\/247\/revisions\/795"}],"part":[{"href":"https:\/\/pressbooks.ccconline.org\/astronomy\/wp-json\/pressbooks\/v2\/parts\/222"}],"metadata":[{"href":"https:\/\/pressbooks.ccconline.org\/astronomy\/wp-json\/pressbooks\/v2\/chapters\/247\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/pressbooks.ccconline.org\/astronomy\/wp-json\/wp\/v2\/media?parent=247"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/pressbooks.ccconline.org\/astronomy\/wp-json\/pressbooks\/v2\/chapter-type?post=247"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/pressbooks.ccconline.org\/astronomy\/wp-json\/wp\/v2\/contributor?post=247"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/pressbooks.ccconline.org\/astronomy\/wp-json\/wp\/v2\/license?post=247"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}