A science museum displays Fig. 1 to compare the apparent movement of stars during one night. The camera was fixed on a tripod and its shutter was left open....
Question 1 Report
A science museum displays Fig. 1 to compare the apparent movement of stars during one night. The camera was fixed on a tripod and its shutter was left open. The curved trails are centred on a point close to the north celestial pole. Visitors ask why the stars appear to move although their positions change very little over one night.
(a) What motion of Earth causes the trails in Fig. 1? [1]
(b) When does Earth complete one rotation? [1]
(c) Describe the direction of Earth's rotation as seen from above the north pole. [1]
(d) Give two effects of Earth's rotation on people at one location. [2]
A group in the school observatory records the appearance of the Moon at sunset for several evenings. Fig. 1 shows three positions of the Moon in its orbit, viewed from above the north pole of Earth. Half of the Moon is always lit by the Sun. The students use the diagram to plan a public viewing session.
(a) Which position, A, B or C, gives a full Moon as seen from Earth? [1]
(b) What is the name of the phase at position A? [1]
(c) Describe how the Moon produces the light seen by the students. [1]
(d) Give two reasons why a Moon phase is not caused by Earth's shadow. [2]
Answer Details
Star trails
(a) The trails are caused by Earth’s rotation on its axis [1].
(b) Earth completes one rotation in 24 hours, or one day [1].
(c) Seen from above the north pole, Earth rotates anticlockwise [1].
(d) Two effects at one location are day and night [1] and the apparent daily movement of the Sun or stars [1]. Changing shadow direction is also accepted.
Moon phases
(a) A full Moon is at C [1]. At this position, Earth is between the Sun and Moon, so the illuminated side faces Earth.
(b) At A the phase is a new Moon [1].
(c) The Moon reflects light from the Sun [1]. It does not produce its own visible light.
(d) Earth’s shadow reaches the Moon only during a lunar eclipse [1], whereas phases occur every month. The changing angle from which Earth sees the Moon’s sunlit half causes the phases [1]. Half of the Moon is illuminated by the Sun at all times.
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