5. The Moon and Its Phases.pdf

Lesson 5 The Moon and It’s Orbit The Moon’s Orbit ▪ The orbit of the Moon around the Earth moves from east to west along a path oriented at about 5.2 degrees to the Earth’s orbital plane. ▪ We always see the same face of the moon because as the Moon moves along its orbit around the Earth, the Moon...

Lesson 5 The Moon and It’s Orbit The Moon’s Orbit ▪ The orbit of the Moon around the Earth moves from east to west along a path oriented at about 5.2 degrees to the Earth’s orbital plane. ▪ We always see the same face of the moon because as the Moon moves along its orbit around the Earth, the Moon spins on its axis at just the right rate to keep the same side visible ▪ This synchrony developed over geologic time because the tug of the Earth’s gravity generates a small tidal bulge on the Moon’s surface, friction does not allow this bulge to move as fast as the Moon spins, so the Earth pulls on one side slightly more than on the other, slowing the Moon’s spin until it locked into a rate that keeps one side facing the Earth. This is called tidal locking or sysnchronous rotation ▪ The tidal forces are caused by the gravitational pull of the two bodies. The gravitational pull of the two bodies is also a result of the masses of the two bodies. The smaller the mass of one body with respect to the other, the quicker it will get tidally locked. ▪ This synchrony of this tidal locking is not perfect, though so we actually see 59% of the Moon’s surface over the course of the month Figure 21.17c Movement of the Moon The Moon’s Orbit ▪ The Moon does have a real physical impact on our lives, for instance through its gravity pull (tidal cycles) and, especially on a full Moon, its reflected nocturnal illumination. ▪ Some aspects of animal life are also governed by the monthly lunar cycle, such as when eggs hatch in many species including tortoises and butterflies, or guiding bird migrations. Figure 21.17c The Tides ▪ Tides caused by pull of Moon’s gravity on Earth ▪ High tide – • Side facing Moon and side away from Moon • Every 12 hours, 25 ½ minutes ▪ Low tide – • On other sides of Earth Phases of the Moon ▪ The Moon is 384 000 km away, the Moon moves in its orbit at 1 km/s (3600 km/h) ▪ The Moon is visible because of reflected sunlight. (nonluminous) ▪ As the Moon orbits the Earth, different amounts of it are visible as the angle between the Sun-Earth-Moon changes. ▪ This produces the visible cycle called phases. ▪ This cycle takes 29.5 days (synodic month) ▪ Lunar months were once the basis of calendars, but they don’t work well because they get out of synchrony with the seasons ▪ At a full Moon the whole Moon is visible and at a new Moon none is visible. Figure 21.18 It’s Just a Phase ▪ Moonlight is reflected sunlight ▪ Half the moon’s surface is always reflecting light ▪ From Earth we see different amounts of the Moon’s lit surface ▪ The amount seen is called a “phase” Waxing and Waning ▪ New moon ▪ Waxing Crescent moon ▪ First Quarter moon ▪ Waxing Gibbous moon ▪ Full moon ▪ Waning Gibbous moon ▪ Third Quarter moon ▪ Waning Crescent moon ▪ New moon last (third)quarter waning Moon moon orbit`s earth SUN gibbous moon crescent earth full moon new moon gibbous moon crescent waxing Moon first quarter FOUR MAIN SHAPES FULL QUARTER CRESCENT GIBBOUS Phases of the Moon ▪ ▪ ▪ ▪ ▪ A new moon occurs as the moon rises at approximately the same time as the Sun, so the Sun is behind the Moon, and the side of the Moon facing us is shaded Every night after the new moon, the visible part of the Moon waxes, or grows, as sunlight illuminates a progressively larger part of the Moon’s surface Moon passes sequentially through phases knows as the crescent Moon, quarter Moon, and gibbous Moon, half way through a lunar month, the Moon rises as the Sun sets, and the entire face of the Moon that we see from the Earth is lit, producing a Full Moon On subsequent days, the Moon rises progressively later than the Sun sets so the lit portion seen from the Earth wanes, or shrinks, through gibbous, quarter, and crescent phases The cycle comes to completion when the Moon is once again in its new phase Figure 21.18 Eclipses Plane of earth’s orbit Moon Earth Moon Plane of lunar orbit Lunar Eclipses ▪Moon moves into Earth’s shadow – this shadow darkens the Moon • Umbra- complete darkness • Penumbra- some light ▪About 2-3 per year at different locations ▪Last up to 4 hours Nature of Eclipses ▪ The Moon has a radius of 1737 km which is much smaller than the radius of the Sun’s which is 695 800 km but because of the closeness of the Moon as viewed from the Earth, the moon and the Sun appear to be almost identical in size ▪ An eclipse occurs when the Moon or the Earth passes through the other’s shadow. ▪ Normally the Moon’s orbit is tilted compared to the Earth, so it does not cross the Earth-Sun line. ▪ An eclipse can occur when the Moon crosses the Earth or the Sun during a new Moon (solar eclipse) or a full Moon (lunar eclipse). Figure 21.19 Lunar Eclipse ▪ A lunar eclipse happens when the Moon passes behind the Earth, blocking the light of the Sun during a full Moon. • Here, the Moon looks red because sunlight that passes through the Earth’s atmosphere is bent toward the Moon, and is reflected off the surface of the Moon • About 35% of all lunar eclipses in a calendar year are total lunar eclipses. On average, a total lunar eclipse can be seen from any given location every 2.5 years. Figure 21.20c Solar Eclipse ▪ A solar eclipse occurs when the Moon passes directly between the Earth and the Sun at a new Moon. • The distance between the Earth and the Moon determines the type of eclipse seen. • T is the area of total eclipse, and P is the area of partial eclipse. • Annular eclipses occur when the Moon is too far from the Earth to completely block the Sun. • Shadows that occur when objects obscure light from a nonpoint source of light (a source with significant width) consists of two parts, umbra (complete darkness) and penumbra (partial darkness) • Solar eclipses are fairly numerous, about 2 to 4 per year, but the area on the ground covered by totality is only about 50 miles wide. In any given location on Earth, a total eclipse happens only once every hundred years or so, though for selected locations they can occur as little as a few years apart. Figure 21.20a Lunar Eclipse Figure 21.20c Exploring the Moon ▪1950s to 1960s – probes (see above ▪Neil Armstrong -First man on the Moon – July 20, 1969 ▪Six Apollo missions (1969-1972) • 382 kg (842 lbs) rocks ▪12 Americans have walked on the moon When will we return? Artemis II, is scheduled to take place in November 2024 with the four-person crew circling the Moon but not landing on it. As part of the Artemis program, NASA aims to send astronauts to the Moon in 2025 Moon base of the future? ▪What would you need to live there? Name this phase! What time does this phase rise and set? Does this image show us the near side or far side of the moon? How can you tell? Compare illumination of the near and far sides? Homework Moon Assignment