Moon Phases Online

ASTRONOMY 112/130 MOON PHASES Moon Phases Objectives In this laboratory activity you will: ● Learn how the Moon's position in its orbit causes us to see the Moon's phases as well as the 8 names we use for those phases ● Learn to distinguish between the Moon's near side and its far side ● Learn to distinguish between the Moon’s lit side and dark side ● Learn the difference between the Moon's limb and terminator. ● Use on online lunar calendar to answer some questions about when and where you can see different phases Background Information The Moon’s Orbit: The Earth has one natural satellite called The Moon . The Moon orbits the Earth in about four weeks. The Moon's orbit is not a perfect circle, it is an oval shape called an ellipse . And the Earth is not at the center of the orbit. The Earth is closer to one end and farther from the other end. The spot on the Moon's orbit which is the closest to the Earth is called perigee (from "peri" which means "near", and "gee" which means "Earth") while the spot which is the farthest from the Earth is called apogee (from "apo" which means "away" and "gee"). The Moon takes 27.3 Earth days to go from perigee to perigee again (one full orbit). The Moon does appear larger in the sky at perigee than apogee, but you can’t tell the difference just with your eyes (you’d need to take a photo of it at the two times and compare them to notice the difference). Shadows Don’t Cause Moon Phases: As the Moon orbits the Earth, the Moon has sunlight shining on it. It is true that 2 to 5 times a year, the Moon goes into the Earth's shadow (which is called a lunar eclipse ), but we will not deal with these occurrences in this lab. It is a somewhat common misconception that the Earth’s shadow causes the Moon’s phases, but that’s not true. Lit and Dark Sides of the Moon: At any one time, one half of the Moon's surface is illuminated by the Sun while the other half is dark. These two hemispheres of the Moon are called the lit side or daytime side and the dark side or nighttime side , respectively, and the imaginary dividing line between them is called the terminator . The terminator is the dividing line between day and night on the Moon's surface (or any other celestial body). It is the border between the lit side and the dark side. The lit side and the dark side of the Moon are constantly changing as the Moon orbits the Earth. Near and Far Sides of the Moon: At the same time, one half of the Moon's surface is facing toward the Earth while the other half is facing away from the Earth. These two hemispheres of the Moon are called the near side and the far side , respectively, and the imaginary dividing line between them is called the limb . The limb is the horizon of the Moon that we see against the background sky. It is the border between the lit side and the background sky. The near side and 1

ASTRONOMY 112/130 MOON PHASES the far side of the Moon are unchanging. We always see the same side of the Moon from Earth, and didn’t see the far side until we sent the first spacecraft to orbit the Moon in the 1960s. 2

ASTRONOMY 112/130 MOON PHASES Moon's orbit around the Earth The outer circle of figures shows how the Moon phases appear in the sky (view from Earth) . The inner circle shows the positions of the Moon when the different phases appear (view from space) . 4 waxing gibbous full waning gibbous new waxing crescent first quarter Earth

ASTRONOMY 112/130 MOON PHASES A. Lunar Phase Timing and Terminology: Assume that the Moon takes four weeks to go through a full cycle of phases (it is actually 29.5 days, but four weeks is close enough). Also assume for these questions that we’re talking about the midpoint of the crescent and gibbous phases (in reality, for example, the Moon is a waxing crescent for almost a week, and the same for waxing gibbous, waning gibbous, and waning crescent). Circle/Underline/highlight the correct answer to each question. 1. How many phases are there (including the new phase)? a. four b. six c. eight d. ten 2. Assuming four weeks to go through all the phases, how many weeks elapse from one major phase to the next? a. half week b. one week c. one-and-a-half weeks d. two weeks 3. Which Moon phase comes right after a waxing crescent Moon? a. full b. new c. waxing gibbous d. first quarter 4. Which Moon phase comes right after a waxing gibbous Moon? a. waning gibbous b. third quarter c. first quarter d. full 5. Which Moon phase comes two weeks after a full Moon? a. waning gibbous b. waxing crescent c. waning crescent d. new 6. Which Moon phase comes two weeks after a waning gibbous Moon? a. first quarter b. waxing crescent c. third quarter d. full 7. Which Moon phase comes two-and-a-half weeks after a waning crescent Moon? a. new b. full c. first quarter d. third quarter 8. Which Moon phase comes three weeks after a new Moon? a. waning crescent b. waning gibbous c. third quarter d. first quarter 9. Which Moon phase comes three-and-a-half weeks after a third quarter Moon? a. full b. new c. waning crescent d. waning gibbous 10. Which Moon phase comes four weeks after a full Moon? 5 Sunlight third quarter waning crescent = Seen from space (i.e. from above) = Seen from Earth NOTE :

ASTRONOMY 112/130 MOON PHASES C. Gibbous Moon Labeling: Below is a picture of a waning gibbous Moon in the sky. Five points on the diagram are labelled. Look at the diagram and answer the following five questions. Circle/underline/highlight your answers. *The little dots on the picture are background stars. 1. Which point is on the Moon's terminator? A B C D E 2. Which point is on the background sky? A B C D E 3. Which point is on the Moon's limb? A B C D E 4. Which point is on the Moon's dark side? A B C D E 5. Which point is on the Moon's lit side? A B C D E 7 B A C D E

ASTRONOMY 112/130 MOON PHASES D. Crescent Moon Labeling: Below is a picture of a waxing crescent Moon in the sky. Five points on the diagram are labelled. Look at the diagram and answer the following five questions. Circle/underline/highlight your answers. *The little dots on the picture are background stars. 1. Which point is on the Moon's terminator? ` A B C D E 2. Which point is on the background sky? A B C D E 3. Which point is on the Moon's limb? A B C D E 4. Which point is on the Moon's dark side? A B C D E 5. Which point is on the Moon's lit side? A B C D E 8

ASTRONOMY 112/130 MOON PHASES F. Appearance of Waxing Crescent Moon: Below are two pictures of a waxing crescent Moon, seen through a telescope. The black dots are background stars behind the Moon and much further away. Which picture would be impossible to see? (circle/underline/highlight) Picture 1 Picture 2 Explain your answer: Picture two would be impossible to see because you would not be able to see stars on the dark side of the moon. G. Moon Phases f or the Current Month : Go to the website: Moon Phase Table in Concord, CA (https://www.timeanddate.com/moon/usa/concord-ca) . In the upper right, type in Concord, CA (the closest location to DVC’s campus). Shown near the top of the page will be a sketch of the current Moon phase and your current date/time. The “percent” number under the Moon sketch tells you how much of the Moon’s lit side you can see from Earth. Remember that half of the Moon is always illuminated, but how much of that illumination we see from Earth depends on our viewing angle. The Moon Phase Table: Below the information and sketch for the current Moon phase is a table that lists the Date (and a tiny picture of the Moon phase for full, third quarter, new and first quarter), Moonrise time, Moonset time, Moonrise time, Meridian crossing time (when the Moon crosses the meridian and is therefore highest in the sky in the south for us), the Moon’s distance from Earth, and finally What Percent of the Lit Side we can see from Earth. For all the times in the table, the Moon’s azimuth is also given. The azimuth tells you where to look along the horizon (recall the horizon coordinates). Use the online calendar given in the link above to answer these questions . Make sure the calendar month matches the current month. 1. On the Moon Phase page, click on the Sunrise & Sunset tab. Write down the sunrise and sunset time for the current day. Date: Sunrise time: Sunset time: 2. Return to the Moonrise and Moonset tab. Which day this month would you be able to see the Moon at its highest point in the sky (meridian) as the Sun is setting ? What is the Moon’s phase? Date: Moon’s Phase: 10 Earth Sunlight

ASTRONOMY 112/130 MOON PHASES 3. Which day this month would you be able to see the Moon at its highest point in the sky (meridian) as the Sun is rising ? What is the Moon’s phase? Date: March 28th Moon’s Phase: Full Moon 4. Find the Full Moon phase for the current month. There may be two Full Moons in a month, but it’s not very common; when it does occur, the second Full Moon is called a “blue moon” (but it’s not actually blue!). Describe where the Sun is when the Full Moon is above the horizon. (You should check the sunrise/sunset times for the specific Full Moon day(s) in the Sunrise & Sunset tab.) The sun and moon are on opposite sides of the earth. H. Moon Phase Photo : There is a separate submission link for this part of the assignment. This part of the lab is worth 20 out of the 100 points for the lab assignment. A full set of instructions is included in the Lab Submission: Lunar Phase Photos link in Canvas. Please see the assignment page for further instructions. 11