ASTR 151 1nd Edition Lecture 2 Outline of Last Lecture I Introduction to class II Hypothesis defined III Model defined IV Scientific Law defined V Beginning Chapter 1 and 1 1 Outline of Current Lecture II 1 4 Earth s Orbital Motion III 1 5 Motion of the Moon IV 1 6 Measurement of Distance Current Lecture o Angular Measure Example The distance from the naked eye to the Moon Theta 31 arc minutes 1 Degree 60 arc minutes 1 arc minutes 60 arc minutes II 1 4 Earth s Orbital Motion a Solar Day Daily cycle is diurnal motion b Sidereal Day stars aren t always in the same place after one Earth rotation c Earth moves around 12 constellations during the year known as the zodiac the path is ecliptic d Ecliptic plane of Earth s path around Sun its tilted 23 5 degrees to the celestial equator e Summer Solstice Northern point of path f Winter Solstice Southern most point of path Both Summer and Winter Solstices points where path crosses celestial equator g A combination between a day length and sunlight makes a season h Precession rotation of Earth s axis Earth makes a complete rotation in about 26 000 years III 1 5 Motion of the Moon a Synodic Month The moon takes 29 5 days to go through a cycle These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute i Moon phases are created by different amounts of sunlit portions that are visible from Earth b Sidereal month time for a full 360 degree rotation around the Earth its two days shorter than Synodic Month i Phases 1 Waxing Crescent 2 3rd Quarter 3 Waning Gibbons 4 Full Moon 5 Waxing Gibbons 6 1st Quarter 7 Waxing Crescent c Eclipses happen when the Earth Moon and Sun form a perfectly straight line i Lunar Eclipses 1 Earth between Moon and Sun light reflected from the Earth ii Solar Eclipses 1 Moon between Earth and Sun 2 Partial when part of Sun is blocked 3 Annular when Moon is too far from Earth for total d Eclipses don t occur monthly because Earth s and Moon s orbit aren t in the same plane IV 1 6 Measurement of Distance a Triangulation i Measure the baseline and then angles This calculates distance ii Use a right triangle for easier use b Parallax i Similar to triangulation but parallax looks at apparent motion of an object against distant background from two vantage points ii Another way to explain how far apart in angular distance an object seems to be c To Measure Earth s Radius i Eratosthenes a Greek mathematician noticed that when the Sun was above in one city it was at an angle to another 2 300 years ago ii Measuring angle and distance between two cities gives us the radius
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