Ch. 28 – The Sun-Earth-Moon System

1. Ch. 28 – The Sun-Earth-Moon System The cosmos radiation as electromagnetic waves are studied by scientists. Radio-Microwaves-Infrared-Visible-Ultraviolet-X-rays-Gamma. Optical Telescopes (2 types) 1. Refracting – 2 lenses (objective & eyepiece. Galileo invented this one. World’s larges is the Yerkes 2. Reflecting – objective, concave mirror, flat mirror, & eyepiece. Newton invented. World’s larges is the Hale Why are most telescopes on a mountain?

2. This is the study of radio waves from space… • Radio Astronomy • Radio waves travel through a vacuum. • Detected day or night with computers. • SETI • The larges single radio telescope is 300 meters in diameter. • Radio Telescope Arrays are radio telescopes arranged in groups, so they act as one telescope. • This creates an interferometry, which improves the radio image twice as much. • These are typically in a Y shape pattern.

3. The Hubble Space Telescope (HST) is the best-known telescope. It was launched in 1990 and will operate until 2010. • Other important probes and satellites include: • Chandra (X-rays), Spitzer Space Telescope (wavelengths blocked by the atmosphere), Sojourner-Spirit-Opportunity (all probes on Mars). • Space shuttle missions are used to study microgravity and its effects on plants, animals, the growth of crystals, and other phenomena. • The International Space Station (2000) is used to study long-term effects of space.

4. The Moon • The last 100 years has brought a lot of new discoveries about the Moon. • Sputnik I (1957) was the first satellite launched. • First human in space – Yuri Gagarin (1961). • First American in space – Alan Shepard Jr. (May 1961). • First on the Moon – Neil Armstrong and Buzz Aldrin (1969). • Most moons are much smaller than the planet they orbit. • The Earth’s moon is the only large moon among the inner planets. Mercury and Venus have no moons at all, and the moons of Mars are just 2 tiny chunks of rock.

5. The Moon’s albedo (light reflection) is about 7% compared to the Earth’s 31%. • Sunlight gets absorbed easily on the Moon’s surface, which is why the surface is as high as 127° C and without sunlight the surface temperature can drop to -173° C. • There is no erosion on the Moon. • There is no atmosphere or flowing water. • Regions : Highlands – mountainous and heavy with craters. Maria – smooth plains. • All the craters are impact craters formed from objects hitting the surface. • Ejecta is the fall back material from an impact and they form long trails called rays.

6. Why so many craters on the Moon and not the Earth? • No atmosphere • No erosion • The Earth had crater impacts, but with erosion only new impacts are visible. • The Moon has a lot of silicates, breccias, and basalts. • The Moon is most likely layered like Earth with a crust, upper mantle, lower mantle, and a core. • Fig. 28-10 (pg. 756) • The crust, upper mantle, and core are solid. The lower mantle is partially molten. • The Moon has no active volcanoes and very slight moonquakes that could rattle dishes on Earth once a year. • This causes scientists to theorize that the Moon has no tectonics.

7. The most supported theory of how the Moon formed is the impact theory. • It formed as a result of a gigantic collision between Earth and a Mars-sized object about 4.5 billion years ago. This occurred when the solar system was forming. • As a result, materials from the incoming body and from Earth’s outer layers were ejected into space, where they then merged together to form the Moon. • Fig. 28-11 (pg. 757)

8. The Sun-Earth-Moon System • It appears that the Moon, Sun, and stars are rotating around the Earth every day. • For years scientists believed this geocentric view point. • We now know that the Earth is rotating 15° per hour. • A pendulum can demonstrate the rotating Earth. • The direction of the pendulum swinging shifts direction with the rotation of the Earth. • We can also demonstrate the rotating Earth with the fact that flowing air and water on Earth are diverted from a a north-south direction to an east-west direction as a result of Earth’s rotation (Coriolis effect).

9. The length of day as we observe it is a little longer than the time it takes Earth to rotate once on its axis. • 365 days a year • Leap year to compensate for this. • Annual changes are the result of Earth’s orbital motion about the Sun. Earth’s orbit around the Sun is ecliptic. Fig.28-13 (pg. 759) • The Earth’s axis is tilted at 23.5°. • This is fixed throughout the year, so seasons occur. • This also causes the Sun to change it’s angle and altitude in the sky. Fig. 28-14 (pg. 759)

10. The position of the Earth and Sun. • Page 760  Draw and go over. • Summer solstice – Sun is directly over head in the sky (at Tropic of Cancer). Occurs on June 21. • The number of hours of daylight is maximum at this day in Northern Hemisphere. • Winter solstice – Sun is directly over head in the sky (at Tropic of Capricorn). Occurs on December 21. • The number of daylight hours is at a minimum in the Northern Hemisphere. • The Sun never rises in the region within the artic circle in the Winter and Summer solstices.

11. The Sun is directly overhead at the equator during the autumnal and vernal equinox. • The Northern and Southern Hemispheres have equal amounts of sunlight during this time. • Sun’s position in the Northern Hemisphere. • Fig. 28-17 (Pg. 762)

12. Phases of the Moon • Lunar Phases • Fig. 28-18 (Pg. 762) • When the Moon is between the Earth and the Sun we can’t see it because no light is reflected. This is called a new moon. • As the Moon moves along in its orbit the amount of light reflected increases. The increasing reflected sunlight is called waxing. • When less than half of the sunlit portion of the Moon is seen this is called a waxing crescent. • When more than half of the sunlit portion of the Moon is seen this is called waxing gibbous.

13. The first quarter of the Moon occurs when we see half of the sunlit side. • A full moon occurs next, in which the Earth is between the Sun and the Moon. • The sunlit side decreases after this. This is called waning. • As in the waxing phases, there is a period during the waning phases when we can see more than half of the sunlit portion of the Moon. • These phases are called waning gibbous and waning crescent. • The Moon reaches a point in the waning phases in which we can see half of the sunlit portion. This is called the third quarter. • Fig. 28-19 (pg. 763)

14. Synchronous rotation – the Moon rotation is equal to it’s orbital movement. • This is why we see the same side of the Moon. • From one full moon to the next is called a lunar month  29.5 days. • The Moon takes 27.3 days to orbit the Earth. • Why the difference? Fig. 28-20 (Pg. 764) • Because the Earth’s position (angle) with the Sun has changed, thus the Moon has to travel 2.2 more days to complete a lunar month. • The Moon’s gravity pulls on Earth’s surface and creates a bulge of ocean water on both the near and far side of Earth. The rotation of the Earth contributes to 2 high and low tides in a day’s time. • A high tide every 12 hours & low tide every 12 hours. Draw.

15. Solar eclipse occurs when the Moon passes directly between the Sun and Earth and blocks our view of the Sun. • The solar eclipse can vary from a partial to a full. • Fig. 28-21 (pg. 765) • Fig. 28-22 • A solar eclipse doesn’t happen every month with each new moon because the Moon’s orbit is tilted 5° relative to the ecliptic. • The closest point in the Moon’s orbit to Earth is called perigee. • The farthest point is called apogee.

16. A lunar eclipse occurs when the Moon passes through Earth’s shadow. • Fig. 28-24 (pg. 767) • A lunar eclipse can only occur during a full moon. • Like a solar eclipse, a lunar eclipse doesn’t occur every full moon because the Moon in its orbit usually passes above or below the Sun as seen from the Earth. • Solar and lunar eclipses occur is almost equal numbers, with slightly more lunar eclipses. The maximum number of eclipses (solar & lunar), that can be seen in a year is 7. • 1982 (last) & again in 2038.