Chapter 4: Phases of the Moon & Planets © BRIEF 20141

2 Phases of the Moon & Planets Overview: Phases of the Moon Lunar Cycle Elements Libration Apogee vs. Perigee Sidereal vs. Solar Time

© BRIEF Phases of the Moon & Planets Phases of the Moon: Tidal Locking Moon is tidally “locked” to the earth: One side of the moon always faces the Earth

© BRIEF Phases of the Moon & Planets Lunar Phases: Another View Caused by rotation of the moon around the Earth Sunlit portions of the moon determine the phases Interval containing all phases = 29 ½ Earth days= 1 rotation Note the green arc at the end…..Sidereal Gibbous: Convex at both edges

© BRIEF Phases of the Moon & Planets Lunar Phases: Earth Shine

© BRIEF Phases of the Moon & Planets Lunar Phases: Earth Shine

© BRIEF Phases of the Moon & Planets Lunar Cycle Elements: Moon orbit inclined 5° to the Earth’s (cause for variations in eclipse cycle) Each day the moon rises about 50 minutes later than then last day

© BRIEF Phases of the Moon & Planets Lunar Cycle Elements: Apogee and Perigee Apogee: Derived from Aphelion-Greatest distance away in an orbit Farthest point from the Earth Perigee: Derived from Perihelion- Closest point in an orbit to the other body Closest point to the Earth For the Moon, hardest to detect unless observing photographs

© BRIEF Phases of the Moon & Planets Perihelion & Aphelion: Orbital Comparison

© BRIEF Phases of the Moon & Planets Perihelion & Aphelion: Orbital Comparison

© BRIEF Phases of the Moon & Planets Lunar Phases: Libration Animation of the Lunar Cycle as seen from Earth. Exhibits Libration. Libration: The apparent oscillating motion of orbiting bodies related to each other. Best seen in the Moon-Earth combination, but existent in other orbits too.

© BRIEF Phases of the Moon & Planets Planetary Phases: Overview Planets undergo phases like the moon although not as pronounced Venus and Mercury are the most pronounced

© BRIEF Phases of the Moon & Planets Planetary Phases: Venus

© BRIEF Phases of the Moon & Planets Planetary Phases: Mars

© BRIEF Phases of the Moon & Planets Planetary Phases: Mars

© BRIEF Phases of the Moon & Planets Planetary Phases: Mars

© BRIEF Phases of the Moon & Planets Planetary Phases: Jupiter

© BRIEF Phases of the Moon & Planets Planetary Phases: Saturn

© BRIEF Phases of the Moon & Planets Sidereal Time vs. Solar Time: Earth’s Orbit Sidereal Time: Derived from Latin sidus meaning Star Time scale based on the Earth’s rate of rotation measured relative to fixed stars 23h 56 min 4 sec Sidereal time follows the stars Solar Time: Time scale based on Sun’s position in the sky Solar time follows the sun 24 h Give or take a few seconds depending on time of year, thus referred to as: “Mean Solar Time” Due to ellipticity of the Earth’s orbit DEMONSTRATION:

© BRIEF Phases of the Moon & Planets Sidereal Time vs. Solar Time: Moon’s Orbit “Sidereal Month” Revolution around the Earth with respect to the Stars 27 1/3 days “Synodic Month” Revolution around the Earth as measured with respect to the Sun 29 ½ days Pasachoff_Fig. 4.5 © Cambridge University Press 2013 DEMO:

Application: Practical Example a 1.We start both our Sidereal Clock and our Solar Clock at 6:36p, December 1, Image a. 2.The next night the Earth completes 1 rotation at 6:32p per the Sidereal clock (~4 mins shorter than the 24-hour Solar Clock) b 1.Look at the position of Rigel, Mintaka, and Betelgeuse in image b. a 2.How do they differ from image a? 3.Now, we wait until our Solar clock reaches 24hrs. c 1.Look at the image c on the right. What is different? b 2.How do the positions of Rigel, Mintaka, and Betelgeuse differ from image b? a bc Phases of the Moon & Planets

3 Day example: Betelgeuse & Rigel rise 4 mins early each day Phases of the Moon & Planets

1 Month example: Betelgeuse & Rigel rise 4 mins early each day 1 Month apart Phases of the Moon & Planets

© BRIEF Phases of the Moon & Planets Demonstrations: Lunar Phases Simulator: Lunar Phase Vocabulary: Planet Phase Positions Indicator: Lunar Phase Quizzer: Phases of Venus:

© BRIEF Phases of the Moon & Planets Questions?

© BRIEF Phases of the Moon & Planets Phases of the Moon: Caused by rotation of the moon around the Earth Sunlit portions of the moon determine the phases Interval containing all phases = 29 ½ Earth days= 1 rotation Phases: Waxing Crescent First Quarter Waxing Gibbous Waxing: Moving Toward Gibbous: Convex at both edges Full Moon Waning Gibbous Waning: Moving away Last Quarter Waning Crescent

© BRIEF Phases of the Moon & Planets Lunar Cycle Elements: Apogee and Perigee Apogee: Derived from Aphelion-Greatest distance away in an orbit Farthest point from the Earth Perigee: Derived from Perihelion- Closest point in an orbit to the other body Closest point to the Earth For the Moon, hardest to detect unless observing photographs

© BRIEF Phases of the Moon & Planets Lunar Cycle Elements: Apogee and Perigee Lunar and Earth Orbit comparison Source: NOAA

© BRIEF Phases of the Moon & Planets Planetary Phases: Overview

© BRIEF Phases of the Moon & Planets Planetary Phases: Overview Planets with orbits outside of the Earth’s always appear near, to fully, lit. The angular diameter of their disk will grow and shrink as the distance from Earth changes Overhead at midnight is closest, largest and brightest DEMONSTRATION: TheSky Center Saturn Select Celestial Sphere Advance time one Lunar Month at a time Watch the shadow change behind the planet

© BRIEF Phases of the Moon & Planets Planetary Phases: Mars

© BRIEF Phases of the Moon & Planets Planetary Phases: Jupiter

© BRIEF Phases of the Moon & Planets Planetary Phases: Saturn DEMONSTRATION: TheSky Center Saturn Select Celestial Sphere Advance time one Lunar Month at a time Watch the shadow change behind the planet

Sidereal Time: Practical Example Question: What does the earth do once a day? Rotates once on its axis – Sidereal Day = 23h 56m 4s Question: What else happens during this time? The Earth moves about the Sun – Solar Day Solar time is also known as “local” time. Question: What are our clocks based on: Sidereal or Solar Time? Solar – 24 hrs Through these two motions, the sun and stars seem to move about the heavens each day. Based on the solar day, stars rise 4 mins earlier each day. Why? Due to the difference in Sidereal and Solar days Remember: Sidereal day = 23h 56m 4s, & Solar day= 24 hours Starting PointSidereal DaySolar Day Phases of the Moon & Planets

Apply what you know: You know, stars rise 4 mins earlier each day due to the difference in Sidereal & Solar Time You know, There are 31 days between December 1 st and January 1 st. Therefore, at what time will Rigel rise on January 1 st in order to be in the same position as it was, relative to you at Duffield Sports center, when the date was December 1 st ? 1 Month apart Phases of the Moon & Planets

© BRIEF Phases of the Moon & Planets Lunar Phases: Sidereal vs. Diurnal (Another View) Daily cycle, noon to noon, is diurnal motion: solar day Stars aren’t in quite the same place 24 hours later, though, due to Earth’s rotation around Sun; when they are once again in the same place, one sidereal day has passed A sidereal day is Earth’s true rotation period—the time taken for our planet to return to the same orientation in space relative to the distant stars. A solar day is the time from one noon to the next. The difference in length between the two is easily explained once we understand that Earth revolves around the Sun at the same time as it rotates on its axis.

© BRIEF Phases of the Moon & Planets Lunar Phases: Sidereal vs. Diurnal (Another View) Frames (a) and (b) are one sidereal day apart. During that time, Earth rotates exactly once on its axis and also moves a little in its solar orbit—approximately 1°. Consequently, between noon at point A on one day and noon at the same point the next day, Earth actually rotates through about 361° (frame c), and the solar day exceeds the sidereal day by about 4 minutes. Note that the diagrams are not drawn to scale; the true 1° angle is in reality much smaller than shown here.