Mapping the Solar System
Some notes on this exercise!
- 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
- 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.