The changing phases of the Moon originally inspired the concept of the month Moon Properties The Moon is in orbit around the Earth, outside the atmosphere. The Moon shines by reflected light (12%) - mostly from the Sun, but some comes from the Earth = Earthshine, which is why you can still faintly see the dark parts of the Moon. 1
Full Moon Because the orbital period of the Moon and the rotation period are the same, the Moon always keeps the same side facing us. 2
The Moon always keeps one face towards us because it rotates at the same rate it orbits Earth Let s use the example of a Porsche on a circular race track. The driver s side always faces towards the inside, where the flag is located. Put the Moon in the place of the race car, and the Earth in the place of the flag. The Far Side of the Moon 3
The Moon goes through changes in its appearance, called Phases. It goes from absent (or New), all the way through completely lit (Full), and back again. The Hebrew, Islamic, Hindu, Chinese, and Japanese cultures all use the lunar phases to build a calendar, instead of the Sun s location throughout the year. 1. New Moon 2. Waxing Crescent 3. First Quarter Moon Phase Names 4. Waxing Gibbous (Gibbous means hunchbacked or bulging) 5. Full Moon 6. Waning Gibbous 7. Third Quarter 8. Waning Crescent 4
New Moon How long does it take to complete the full cycle of Moon phases? A. About a day B. About a week C. About a month D. About a year 5
The Lunar cycle repeats every 29.5 days A Common Misconception: The shadow of the Earth causes the phases of the Moon. There are two observable problems with this model. What are they? 1. As the diagram shows, this model can explain new moon, full moon, and the crescent phases, but not the gibbous phases. 2. The Moon would be full most of the time, except for the short periods that it crossed the Earth s shadow. 6
An important clue: The Moon can be seen during the day! What phase is the Moon in these pictures? If the shadow of the Earth causes the phases, can these pictures be possible? Not only does the Moon go through phases, it rises at different times, depending on the phase 7
Not only does the Moon go through phases, it sets at different times, depending on the phase We need to explain: 1. Why the Moon has phases and why it rises and sets at different times. 2. Be able to predict the phase and the rising and setting times of the Moon before it happens. Then, we can check whether we are right! 8
Although the Moon is always half lit by the Sun, we see different amounts of the lit portion from Earth depending on where the Moon is located in its month-long orbit. Although the phase of the Moon changes, the same side of the Moon still faces the Earth Animations similar to the one shown in class can be found at: https://en.wikipedia.org/wiki/libration https://www.youtube.com/watch? v=vc7odtqhopc Moon Wobble https://apod.nasa.gov/apod/ ap120205.html The wobbling of the Moon you see, called libration, is interesting, but we won t be covering it in this class. 9
We will use this diagram to understand Moon phases. This diagram is exaggerated the Moon and the Sun are much further away from the Earth than this diagram shows. We will also assume that sunrise is at 6am and sunset is at 6pm this is not generally true, but we will assume it here for simplicity. How can we understand the phases of the Moon? Left Lights Last! Left Leaves Last! So, as a month progresses, the Moon 1) changes phases, and 2) rises 50 minutes later each day. 10
What time is it when the waxing crescent moon is highest in the sky? When does it first rise? When does it set? What time is it when the waxing crescent moon is highest in the sky? When does it first rise? When does it set? Use the Moon phase diagram or the rule of six both work equally well. 11
What time is it when the waxing crescent moon is highest in the sky? When does it first rise? When does it set? Use the Moon phase diagram or the rule of six both work equally well. What moon phase would be rising in the East at 3pm? What Moon phase would be setting in the West at 3pm? 12
Lecture Tutorials (2): The Cause of Moon Phases and Predicting Moon Phases p. 81 87 Work with a partner. Say Hi and learn their names. Read the instructions and questions carefully. Discuss the concepts and your answers with one another. Take time to understand it now!!!! Come to a consensus answer you both agree on. If you get stuck or are not sure of your answer, ask another group. If you get really stuck or don t understand what the Lecture Tutorial is asking, ask for help by raising your hand. What phase of the Moon rises in the east as the Sun rises in the east? A. first quarter B. gibbous C. full D. third quarter E. new (use the white side of your sheet) 13
What time is it when the moon phase shown at right first begins to rise above the horizon? A. at midnight B. 7:00AM C. 7:00PM D. at noon E. 3:00AM (use the white side of your sheet) What time is it when the moon phase shown at right first begins to set above the horizon? A. at midnight B. 7:00AM C. 7:00PM D. at noon E. 3:00AM (use the white side of your sheet) 14
If the moon is highest in the sky this morning at 6:00 am, what phase will the moon be in one week from now? A. Full B. Waxing Crescent C. Waning Crescent D. Waning Gibbous E. New (use the white side of your sheet) What is wrong with this picture? Image downloaded from YSU s home page, Spring 2007 15
Eclipses Eclipses The apparent sizes of the Moon and the Sun are both about the same, as viewed from the Earth. The Sun is actually much larger than the Moon, but it is much further away. As a result, occasionally the Moon will pass directly in front of the Sun Solar Eclipse Similarly, the Moon will sometimes pass directly behind the Earth, in the Earth s shadow Lunar Eclipse 16
Solar Eclipse Types Annular Eclipse Partial Eclipse Total Eclipse Types of Solar Eclipses: Total Solar Eclipse: Moon completely covers Solar disk totality only lasts up to 7.5 minutes can view Solar corona Annular Solar Eclipse: (Annular means ring) Moon almost covers Sun due to Moon s elliptical orbit (sometimes the Moon is further away from the Earth) Partial Solar Eclipse Moon only covers part of Sun 17
Moon s shadow during total eclipse from Mir space station An image of a solar eclipse over Turkey, taken by the International Space Station. 18
As the Moon s shadow is actually quite small, only people in a small area of the Earth can see a total solar eclipse along the eclipse path. However, people in a larger area will be able to see a partial solar eclipse. Solar Eclipse Path : August 21, 2017 Youngstown saw 83% of the moon blocked a partial solar eclipse 19
Solar Eclipse Path : April 8, 2024 The phase of the Moon at a solar eclipse: A. is always full. B. is always new. C. is always waning crescent. D. is always waxing gibbous. E. may be anything depending on the geometry. (use the white side of your sheet) 20
When the Earth s shadow blocks the Sun from lighting up the full moon, it s called a Lunar Eclipse Lunar Eclipse When the Earth blocks most of the sunlight from illuminating the Moon s surface for several hours when in the full moon phase. 21
Types of Lunar Eclipses Total eclipse Partial eclipse Penumbral eclipse 22
Most of the time, the Moon does not entirely disappear, due to refracted (bent) sunlight through Earth s atmosphere Lunar Eclipses The Moon gets a reddish color! Lunar Eclipses are visible over a much larger area than solar eclipses! Eclipses (solar/lunar) do not occur every (New/Full) moon, because the Moon s orbit is not exactly lined up with the Earth s orbit. (The diagram below is exaggerated so you can see the misalignment.) Eclipses happen when the Moon is on the ecliptic. 23
Eclipses occur ONLY when the Moon crosses the plane of Earth s orbit around the Sun (the ecliptic) AND ONLY during the NEW or FULL phases. Which positions cause which eclipses? When the Moon is in the Full phase and is directly in line with the Earth and the Sun, you get a lunar eclipse. When the Moon is in the New phase and is directly in line with the Earth and the Sun, you get a solar eclipse? 24
The Moon s orbit gets slightly larger each year. What effect, if any, would this have on solar eclipses, after a long amount of time? A. There would be more total solar eclipses. B. There would be no effect on eclipses. C. There would be fewer solar eclipses. D. There would be no total solar eclipses, only annular and partial eclipses. E. It may be anything depending on the geometry. (Use the white side of your sheet) The motions of the Sun, Moon and Earth and their effects on the sky 1. The rotation of the Earth causes the day and makes objects in the sky appear to move across the sky and rise and set. 2. The orbit of the Earth around the Sun makes the constellations visible at night change over the year. 3. The tilt of the Earth s axis to its path around the Sun, changes the observed path of the Sun, makes the day longer or shorter and causes the seasons. 4. The relative positions of the Earth, Sun, and Moon cause the Lunar phases and cause Eclipses. 25