Ch08 - Chapter 8 8.1 Lunar phases, tides and eclipses The...

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Chapter 8 Lunar phases, tides and eclipses 8.1 The moon s orbit The moon’s orbit is almost circular. Sidereal period ( 恆星周期 ): The time to orbit around the earth once relative to distant stars = 27.3 days. (This will be made clear when we introduce the synodic period.) The orbit inclines by only 5 ° to the earth’s. the moon always appears near the ecliptic The self-rotation period of the moon is about the same as the sidereal period we always see the same half of the moon from the earth 8.2 Phase cycle ( 月相循環 ) Fig. 8-1 The moon’s motion around the earth produces phases.
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UGB 240M Astronomy The moon 8-2 Phase cycle: New moon Waxing crescent First quarter Waxing gibbous Full moon Waning gibbous Third quarter Waning crescent New moon (Fig. 8-1). New moon ( 新月 ): The moon is between the sun and the earth. It does not reflect sunlight towards us, and so we cannot see the moon at night. Waxing crescent ( 漸滿蛾眉月 ): A thin slide of the moon is lit (crescent). The moon sets shortly after sunset, appearing above the western horizon. First quarter ( 上弦月 ): The moon is half-lit. It is at the highest position at sunset, and it sets at midnight. Waxing gibbous ( 凸月 ): A large portion of the moon is lit (gibbous). It rises shortly before sunset. Full moon ( 滿月 ): The moon is opposite to the sun and is full-lit. It rises in the East at sunset, and it sets at sunrise. Waning gibbous ( 殘月 ): The phase is gibbous. It rises shortly after sunset. Third quarter ( 下弦月 ): The moon is half-lit. It rises at midnight. Waning crescent ( 漸暗蛾眉月 ): The phase is crescent. The moon rises shortly before sunrise, appearing above the eastern horizon. A simple way to determine when the moon rises/sets (Fig. 8-2). Fig. 8-2 In this figure, the age of the moon in a phase cycle is about 4 days. The observer’s time is about 9 pm (determined from the position of his zenith). Now the moon is setting. 1. Draw a circle to represent the moon’s orbit and several arrows to represent sunlight. 2. Write down 0 day, 7 days, 14 days and 22 days, which are ages of the moon, as shown in Fig. 8-2. 3. Also write down 6 am, 12 pm, 6 pm and 12 am. 4. Read the age of the moon from the calendar and put the moon at the appropriate position in its orbit.
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UGB 240M Astronomy The moon 8-3 5. Then we can rotate the earth, the observer and the line representing the ground together to see when the moon will rise and set. The observer’s time can be determined from his zenith.
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This note was uploaded on 04/03/2011 for the course PHYSICS 101 taught by Professor Tiu during the Spring '11 term at HKU.

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Ch08 - Chapter 8 8.1 Lunar phases, tides and eclipses The...

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