1. Illustrating Desargues’s Theorem

2. Triangles ABC and A'B'C' are perspective from the point O
and perspective from the line o.

3. Desargues’s Theorem: If two triangles are perspective
from a point, they are perspective from a line.

5. How to Make an A in Art

6. Draw the shadow to Make an A!

20. Observe the connection with Desargues’s theorem.

21. Now suppose that instead of a streetlight…

22. Watch how the shadow changes as you click back
the point O is the moon.
Watch how the shadow changes as you click back
and forth between this slide and the previous one!

23. What’s the secret to drawing this new shadow?

24. Idealize: the earth as an infinite plane,
the moon as a giant streetlight…
thousands of miles high, and
thousands of miles away!

25. Then proceed as before!

26. Some great tips for drawing shadows can be found in
Perspective for Artists
By Rex Vicat Cole
Dover, New York, 1976