Mapping the Solar System

• Note that in this exercise, the words heliocentric and geocentric refer to viewpoints rather than the specific models discussed (later) in the text. The geocentric perspective is the view from Earth looking up into the southern sky, while the heliocentric perspective is the view of the Solar System looking down from above. Don't get confused!
• Note that in every diagram, the filled circles/dots represent objects (like the Sun, planets, or the moon). The line circles represent the orbits of the planets. The Sun is always the filled dot in the middle of all of the circles. In every case, when there is a small filled dot on a small line circle which lies on a larger line circle, that represents the moon and its orbit around the Earth (the larger filled dot). (I hope that's clear! Easier to draw than say, so look at the labelled examples!)
• I always started every question by figuring out where the observer would have to be sitting on the Earth in order to be at noon, and worked from there. Anything on the opposite side of the Earth from that point will be high overhead at midnight.
• Remember that the Earth rotates counterclockwise when viewed from above the North Pole!
• If you're having trouble following this exercise, I suggest you take a ball-point pen with a clip. Insert a piece of paper between the pen and the clip (cash register receipts sometimes work well). Now place the pen on the dot representing the Earth. Imagine your observer is at the location of the clip. The piece of paper is his horizon - he can't see behind it! This may help you find the location of the observer for various times, and clarify what will be where in the sky.

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