Fig. 1 shows four positions of the Moon in its orbit, viewed from above the north pole of the Earth. Sun light travels from left to right. A science club us...
Question 1 Report
Fig. 1 shows four positions of the Moon in its orbit, viewed from above the north pole of the Earth. Sun light travels from left to right. A science club uses this model before planning an evening telescope session. The Moon does not make its own visible light. Different amounts of the illuminated half can be seen from the Earth during the month.
(a) State the position, P, Q, R or S, at which a full Moon is seen from the Earth. [1]
(b) Explain why the Moon is visible even though it is not a star. [2]
(c) State which position gives a new Moon. [1]
(d) Describe the change in the visible illuminated area between a new Moon and a full Moon. [2]
(e) Complete this statement: the Moon takes about ______ days to orbit the Earth relative to distant stars. [1]
(f) Explain why the Moon remains in orbit instead of moving in a straight line. [3]
Answer Details
(a) A full Moon is seen at position R, where the Earth is between the Sun and Moon, so the illuminated face is directed towards Earth. [1]
(b) The Sun provides light, and the Moon reflects this sunlight towards the Earth. The Moon is visible by reflected light, not because it produces its own visible light. [2]
(c) A new Moon occurs at position P. [1]
(d) From new Moon to full Moon, the visible illuminated area increases, from none or almost none to the whole visible face. [2]
(e) The Moon takes about \(27.3\) days, or about \(27\) days, to orbit Earth relative to distant stars. [1]
(f) The Moon has a forward velocity, but Earth's gravitational force pulls it towards Earth. This continually changes the direction of the Moon's motion, producing an orbit rather than straight-line motion. [3]
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