The Phases of the Moon, Eclipses, and Tides

1. The Phases of the Moon, Eclipses, and Tides

2. The Moon • The moon is earth’s only natural satellite • The moon orbits/revolves around the earth • It is believed that the Moon and the Earth were formed at the same time from the same nebulae that created the planets. The moon, being smaller, was probably captured by the earth’s gravity. • The moon’s rotation is equal to its revolution around the earth, and therefore we only see one side of the moon at all times. The only people who have seen the other side (the dark side) have been the astronauts.

3. The earth has other objects orbiting around it, we call these artificial satellites. • In 1957, USSR put up the first satellite (Sputnik I) • 14,000+ artificial satellites have been launched since then. • USA, Russia, Japan, Canada, India, China, Australia, Europe. • some are communication satellites, military satellites, remote sensing satellites, weather satellites, GPS satellites etc.

4. The moon has no atmosphere • The moon is 376, 275 km away from the earth • The moon has no light of its own, it is all reflected light from the sun • The moon was visited by humans in 1969. Twelve men have visited the moon • The moon has two basic features: The flat lands called Seas and the uneven land made up of impact craters. • Because the moon is so small its gravity is weak. A human would weight 1/6 of his/her weight on the moon.

6. The Phases of the Moon • The moon’s orbit takes it around the earth in approximately 30 days. • Phases of the moon are the apparent changes in shape due to the changing illumination of the moon by the Sun, as seen from Earth. Moonlight is just reflected sunlight. • Please refer to the next slide for a wonderful diagram. Also on the web page there is an excellent animated GIF illustrating the phases of the moon. • A ‘New Moon’ is when you cannot see the moon at all. The night side faces the earth. • A ‘Full Moon’ is when you see the entire day half of the moon.

8. A “waxing” moon is when you see more and more of the moon each night. • A “waning” moon is when you see less and less of the moon each night. • it takes 29 and half days to go from new moon to new moon (this is called a lunar month) • it takes 27 and half days for the moon to go once around the earth (this is called a sidereal month) • it takes about two extra days for the moon to go from new moon to new moon because as the moon rotates around the earth, the earth is revolving around the sun, the two extra days is for the moon to catch up to this new position.

9. New Moon - to observer on earth. Sun Earth Moon

10. Sun Moon Earth 27.5 days later (a sidereal month), the moon has moved 3600 in its revolution about the earth. But to an observer on the Earth directly under the sun, the moon will NOT appear “new” Why? Because during this period the earth-moon system has also moved in it’s orbit about the sun, and therefore sun, moon and earth are not lined

11. Sun Moon Earth To have the three objects in line (for a new moon to be observed on earth) takes about another 2.5 days. So a true lunar month, from new moon to new moon, is 29.5 days.

12. Another way of looking at the same thing.

13. It was the moon’s position in the sky that established one moonth= one month • However, 12 periods of 29.5 days equal 354 days • Hence, the problem of eleven (11) extra days and the awkward attempt to solve it by varying the lengths of the months

14. Eclipses: Solar and Lunar • Both the earth and the moon cast long shadows into space • When either the earth or the moon pass through these shadows, it is known as an eclipse • There are two kinds of eclipses

15. Solar Eclipse • When the moon passes directly between the sun and the earth, the moon “blocks out”or eclipses the sun • Occurs during the day, in the phase of the new moon • A solar eclipse can be total, if the entire sun is eclipsed, or partial, if only a section of the sun is hidden from view. If we see the moon inside the Sun it is called an Annular Eclipse • The maximum duration is 7 min and 30 seconds • It is during this time that we can see the Corona of the Sun.

16. There are two types of shadows created. A ‘penumbra’: outer shadow/partial eclipse/not total black out and an ‘umbra’: inner shadow/total eclipse/total black out This is called a ‘Diamond Ring’ We can see the Sun’s Corona

17. Total Solar Eclipse and the Path of Totality http://www.mreclipse.com/Special/SEprimer.html

18. Orbit of the Moon around Earth “Side” view of the orbits of the earth and moon and sun Plane of moon’s orbit about the earth 50 Plane of earth’s orbit (ecliptic) about the sun This difference between the plane of the earth’s orbit about the sun and the moon’s orbit about the earth accounts for the fact that we don’t have an eclipse each time the moon passes between the sun and earth.

19. Another image of the inclination of the moon’s orbit vis-a-vis the earth’ orbit.

20. Lunar Eclipse • During the night, in the phase of the full moon, the earth may come between the moon and the sun. People on earth will see the shadow of the earth on the moon, causing a lunar eclipse. In other words the moon passes through the earth’s shadow and we get to see it. A lunar eclipse does not happen every full moon because the moons orbital plane is tilted from that of the earth’s. • When the moon is being eclipsed by the earth, it is not completely blacked out in the way the sun is during a total solar eclipse instead, the moon appears as a dull red ball, lit by a small amount of sunlight refracted to it through the earth’s atmosphere. It may last up to 2 hours.

21. http://www.mreclipse.com/Special/LEprimer.html

22. The Moon and Tides • Tide is the name given to the periodic rise and fall of the sea. • Tides are caused mainly by the gravitational pull of the moon and the sun pulling on the waters of the earth, thus causing them to bulge. The moon has a greater effect on tides because it is closer to earth. • The gravitational pull of the moon causes two bulges in the earth’s oceans. One occurs on the side facing the moon and the other on the opposite side, this is a compensatory bulge due to the earth’s centre of gravity and its rotation. These bulges are called high tide. The other two areas on the earth are said to be in low tide. The diagram on the next few slides will explain.

23. Since the earth makes one complete rotation every 24 hours, every place on earth should receive two high tides and two low tides. The tides are approximately 12.5 hours apart. • The difference in water level between high and low tide is known as the ‘tidal range’. On most coasts it is commonly 2 - 4 meters. In enclosed seas like the Caribbean it is usually less than a meter and in the Mediterranean it is almost zero. Certain places experience a very great tidal range owing to the funnel like nature of the bay. The Bay of Fundy in Nova Scotia has a tidal range of about 12 - 15 meters. • When the moon and the sun are aligned with the earth the high tides are higher and the low tides are lower, these are called ‘Spring Tides’. Spring tides occur twice a month. When the moon, earth and sun form a right angle with each other the high tides are a bit lower and the low tides are a bit higher. This situation is called a ‘Neap Tide’.

25. Tides are important for a number of reasons: • They have a great impact on navigation in coastal waters and harbours and are a factor to be taken into account in the design of harbour installations. • In bays and lagoons, they are partly responsible for landforms called tidal or mud flats that can occur at spring tides. • High tides can provide hydroelectric power. • Problems: expensive, engineering difficulties environmental concerns (Bay of Fundy)