C11 : The Sun – Earth – Moon System

Project Choose a planet, moon, star, asteroid, galaxy to research. Describe : size (how many times bigger or smaller than earth) distance (from Earth) composition physical characteristics who discovered it when was it discovered

Typed Point form Pictures Work in pairs HW grade

Section 1 : Earth

List some of the physical properties of Earth 1.Spherical (not a perfect sphere) Shadow on moon by Earth

Q: From Table 1 p.307, how do we know that Earth is not a perfect sphere ? Due to Earth’s rotation. Demo: balloon

2. Earth is rotating about its own axis →day and night 3. Earth is revolving (orbiting) → a year

Q: Imagine what would happen if Earth’s rotation is slowed by 2x → 48 hours a day Warmer in the day Colder at night Different daily habits → may take nap in the day and work longer at night

Earth’s orbit around the Sun is an ellipse. The Sun is not at the center of the ellipse.

Earth nearest to Sun – Jan 3 rd Earth farthest from Sun – July 4 th Q: Does this elliptical orbit cause seasonal temperatures on Earth? A: No. If it did, you would expect the warmest days to be in Jan. This is not true in the northern hemisphere.

4. Earth has magnetic field. due to rotation of Earth and the movement of material inside Earth’s core. Earth’s magnetic field protects us from harmful solar radiation (charged ptles). Note: Pic on p. 308 is wrong!

The angle between magnetic axis and rotational axis is 11.5°. Demo: Create a compass (p. 308)

5. Gravity

Earth’s axis is tilted 23.5° from the vertical line. Earth’s tilted axis and its revolution around the Sun cause the seasons.

The hemisphere that is tilted toward the Sun receives more hours of sunlight each day than the hemisphere that is tilted away from the Sun. Demo : place a globe in front of a flashlight, tilt the globe. Rotate the globe to see how light affects the hemisphere.

In Summer, north pole → 24 hrs daylight south pole → 24 hrs darkness In conclusion, summer occurs in the hemisphere tilted towards the Sun when its radiation strikes Earth at a higher angle and for longer periods of time. Light strikes the Earth at a lower angle during winter and for shorter periods of time.

Solstices Solstice occurs twice in a year. Winter solstice : 12/21 or 12/22 Summer solstice : 6/21 or 6/22 (referring to northern hemisphere) Summer solstice – when the sun appears to be at its greatest and the day is at its longest. Winter solstice – least amount of Sun.

During the summer solstice in the northern hemisphere, the Sun is directly over the tropic of Cancer. During the winter solstice, the Sun is directly over the tropic of Capricorn.

Equinoxes Occurs when the Sun is directly above Earth’s equator. Occurs 2 times in a year. Spring Equinox and Fall (Autumn) Equinox. At equinox, the Sun strikes the equator at 90°. During an equinox, the number of daylight hours and night-time hours is nearly equal all over the world. → 12 hours each. At this time, neither the northern nor the southern hemisphere is tilted towards the Sun. Northern hemispher : spring equinox → 3/20 or 3/21 fall equinox → 9/22 or 9/23

Section 2: The Moon The moon’s revolution around the Earth is responsible for the changes in its appearance. Q: Do we always see the same side of the moon from the Earth? A: Yes. The rotational speed of the Moon and the revolving speed of the Moon are the same. ~27.3 days Demo: lab equipment

Moon Phases Different forms that the Moon takes in its appearance from Earth. The phase depends on the relative positions of the Moon, Earth, and the Sun. New Moon – Moon between Sun and Earth.

1 lunar cycle → 29.5 days. The discrepency between 27.3 days and 29.5 days is due to Earth’s revolution. The extra 2 days are what it takes for the Sun, Earth and Moon to return to their same relative positions.

The moon takes 29.5 days to complete one synodic cycle. This cycle is what we observe from earth, and it is the cycle we would measure from, say, one full moon to the next. However, by the time a synodic cycle ends, the moon has rotated a little more than 360 degrees. This is hard to grasp and takes some time and thought. The rotation of bodies that are orbiting other bodies always presents a need to distinguish between synodic and sidereal rotation. The true, 360 degree sidereal rotation of the moon takes earth days. See links on the moon, and on synodic and sidereal periods.

Q: what causes solar eclipse ? Q: During which phase do you think a total solar eclipse could happen? Q: What causes lunar eclipse ? Q: During which phase do you think a total lunar eclipse could happen?

An eclipse can only occur when the Sun, the Moon, and the Earth are lined up perfectly.

Partial solar eclipse

Lunar eclipse

Q: Is it possible to see a solar eclipse at night? A: No. If we look at the solar eclipse geometry, the side of the Earth observing the solar eclipse is the daytime.

During a total lunar eclipse, we will observe a full moon, less bright and a bit reddish due to diffraction and absorption of other colors as light passes through the atmosphere. Q: Why do less people see total solar eclipse? A: solar eclipse has smaller umbra region.

The Moon’s surface Maria – craters (impact basin) filled with ancient lava. It is dark, dry and flat.

The Moon’s Origin Impact theory

What will you use to survive on the Moon? You have crash-landed on the Moon. It will take one day to reach a moon colony on foot. The side of the Moon that you are on will be facing away from the Sun during your entire trip. You manage to salvage the following items from your wrecked ship: food,rope, solar-powered heating unit, battery-operated heating unit, oxygen tanks, map of the constellations, compass, matches, water, solar-powered radio transmitter, three flashlights, signal mirror, and binoculars.

Hints: 1.Which items will be of no use to you? 2.Which items will you take with you? 3.Describe why each of the salvaged items is useful or not useful.