Astronomy Science Lesson
Phases of the Moon
Unlike the sun, the moon does not give off its own light; instead it reflects the sun’s light. Because of the orbit of the moon, we don’t always see the whole moon illuminated. How much of the moon we see depends on the phase it is in. Over the course of a month, you can observe all the different phases. A great way to teach your children about this is to observe the moon every few nights and discuss which phase it is in. If you have binoculars or a telescope, be sure to use them in your observation! During the month, what other changes do you notice? Does the moon always appear to have the same color and size? Your kids might enjoy keeping a journal with sketches and observations of each stage.
There are eight main phases in the moon’s monthly cycle:
|New Moon– the sun, moon, and earth are lined up, with the sun’s light reflecting off the side of the moon facing it. To the earth on the other side of it, the moon appears to be very dark at this stage.|
|Waxing Crescent– the stage between the new moon and first quarter; a sliver of brightness is visible on the right. The dark part of the moon is still what is most visible to Earth at this point.|
|First Quarter – the moon is to the left of the earth and sun (moving counter-clockwise); the sun’s rays shine on the half of the moon facing it, half of which is visible to Earth. Thus, it appears to be a ‘half moon,’ half bright and half dark.|
|Waxing Gibbous – the stage between the first quarter and full moon, when most of the bright side is visible.|
|Full– the sun, earth, and moon are lined up, with the side of the moon facing the earth illuminated.|
|Waning Gibbous – occurs after the full moon; the right edge appears to be dark or invisible. The moon is in the position opposite where it is during its waxing gibbous stage.|
|Last (Third) Quarter – the moon is to the right of the earth and sun; because the sun’s light only falls on the side of the moon facing it, there also appears to be a ‘half moon’ in this phase. The side that is bright is now opposite where it was during the first quarter, since the moon is on the other side of Earth.|
|Waning Crescent – occurs between the last quarter and the new moon; only a crescent of the bright side shows, on the left edge closest to the sun. The rest of the moon facing us is the ‘dark’ side.|
If you look at a star chart, you’ll see that stars are often shown in groups or patterns called constellations. To help keep track of where stars and locate constellations, astronomers have created something called the celestial sphere, which is an imaginary clear ball surrounding the Earth. You can think of it like this: all of the stars and groups of stars that form constellations are attached to a clear sphere surrounding the Earth. Even while Earth rotates, the sphere stays still, causing it to seem like the stars are moving across the sky! In reality, the stars are not on a sphere and are not even moving. They are simply located in outer space and Earth is simply rotating on its axis and orbiting the sun. Because the imaginary sphere stays still, astronomers are able to use it to keep track of where objects are located in the night sky even as the Earth moves. Observing the stars can be a fascinating and rewarding occupation.
Some useful tools for your observations are a star chart, compass, and binoculars. If your star chart does not glow in the dark, you will probably need a flashlight, as well. If possible, cover the flashlight with red cellophane, since red light is not so distracting to your nighttime vision. To enhance your view of the stars, try getting as far away from bright lights as possible-if you live in the city, a park might make a good observation point.
Constellations change with the seasons because of the earth’s rotation around the sun, so the stars that are visible to us vary from month to month. A good introduction to the study of the stars would be to observe the following constellations, which should be visible during November and early winter. You can download a good quality star chart at www.skymaps.com/downloads.html
Andromeda – ‘The Princess’, ‘The Chained Maiden’. The mythical Andromeda was an African princess, who was to be sacrificed to a sea monster in order to pacify the angry gods. She was rescued by Perseus and became his wife.
Cassiopeia – ‘The Queen’. The mythical character whom this constellation derives its name from was the mother of Andromeda. She aroused the anger of the gods by boasting of her beauty.
Pegasus – ‘The Winged Horse’. The Pegasus supposedly sprang up from the blood of the many-headed Medusa, who was killed by Perseus.
Pisces – ‘The Fish’. The ancient Babylonians, Greeks, and Persians all called this constellation by their name for ‘fish’.
Pleiades – ‘The Seven Sisters’, located in the constellation Taurus. Ancient Greek sailors would not set sail unless this cluster of stars was visible; if they could not see it, it meant bad weather was forthcoming.
Aquila – ‘The Eagle.’ This constellations figures in Greek, Hindi, Japanese, Korean, and Chinese mythology.
Ursa Minor – (Little Dipper). The North Star (Polaris) is at the tip of the ‘handle’.
Perseus – ‘The Hero’. The mythical character Perseus was a Greek who rescued the Princess Andromeda from the sea monster, Cetus. This constellation is most clearly visible in December.
Orion – ‘The Hunter’. This constellation was mentioned in The Odyssey. It is most visible in the winter (January).
Betelgeuse – A star in the Orion constellation. Its name, which comes from the Arabic for ‘house of twins’, is pronounced like ‘BET-el-jooze’.
Ursa Major – (Big Dipper). It probably is not highly visible during the fall or winter.
Astronomy Science Project
Showing Moon Phases
What You Need:
- An orange (or a Styrofoam ball of a size similar to an orange)
- A pencil
- A desk lamp (or any lamp with a removable shade)
- A room that can easily be made dark
- An adult’s help
What You Do:
- Get an adult to help you push the sharp end of a pencil halfway through the orange; push it far enough to keep it stable when you hold the unsharpened end.
- Find a room that you can make dark by turning off the lights and closing shades. If you can’t make it dark enough, do the experiment when it is dark outside or use blankets to cover windows.
- Set the lamp on a table or dresser so it is about the same level as your head when you’re standing. Turn the lamp on and remove the shade or turn the lamp so that the bulb is facing toward you (if you’re using a desk lamp).
- Stand about 3 feet in front of the lamp and hold the pencil with the orange attached to it out at arm’s length. The orange should be between you and the lamp. For this activity, you represent Earth, the lamp is the sun, and the orange is the moon.
- To see the moon’s phases, slowly turn your whole body to the left, keeping your arm straight out in front of you with the orange at eye level. This is how the moon orbits the Earth. Keep turning in the same direction until you have gone in a full circle and are facing the lamp again. Keep your eyes on the orange and watch the shadows on it very carefully to see the phases of the moon as we see them from Earth.
It takes around 29 days for the moon to orbit the Earth once and the same amount of time for the moon to spin around one complete time on its axis. That means that we always see the same side of the Moon! However, we do see the moon changing as it goes through its phases.
While facing the lamp (sun), the surface of the orange (moon) facing you (Earth) was dark, even though the other half of the orange, facing toward the lamp was bright. This is the first phase of the moon, called new moon. We can’t see the moon at all during this phase!
As you began to turn away from the lamp, a shadow still covered most of the orange, but you probably saw a small crescent shape of light on the right side of the orange. This phase is called waxing crescent.
The next phase is called the first quarter: the light (sun) shone on the half of the orange (moon) facing it. From Earth, we see half of the light side and half of the dark side during this phase so sometimes it is called a “half moon.”
As you continued to turn to the left, the light shone on more of the side of the orange you could see, lighting up all of the orange except for a small crescent. This is the waxing gibbous phase.
Once you had turned halfway around so that the lamp was directly behind you, the light (sun) shone directly on the orange (moon) making the whole side facing you bright. This is a full moon. During a full moon, the side facing away from Earth is dark. This phase is the exact opposite of new moon.
(Note: if the orange isn’t fully illuminated, try moving your head or shoulders so you aren’t blocking the lamp. If you are blocking it, you’ve created a lunar eclipse – which happens when the Earth blocks the sun’s light from hitting the moon. Normally, the moon is just above or just below Earth so an eclipse doesn’t happen every time there is a full moon.)
At this point, the amount of the light side of the moon that we can see begins to decrease, or wane. The next phase is called waning gibbous. Most of the moon is still light during this phase.
Next is the last quarter (also called third quarter) where only half of the illuminated side of the moon is visible. This phase is opposite of first quarter. Notice that your back is facing toward the direction you were facing when you saw the first quarter phase!
The last visible phase is the waning crescent, where only a sliver of light is visible. This phase is opposite the waxing crescent. After this, you will be facing toward the lamp (sun) again, and the orange (moon) will be back to the new moon phase!
If you’re having difficulty remembering the difference between waxing and waning moon phases, these rhymes might help:
Waxing: “Moon on the right, getting bigger every night.” (Leading to a full moon.)
Waning: “When the moon is waning, it is fading to the left until there’s no moon remaining.” (Leading to a new moon.)