Lesson 13: Measuring Objects in the Solar System Indirectly Objective: Learn how angular diameter can be used to measure the true diameter of the Moon

Indirect Measurements Objects in the solar system are difficult to measure because of their distance. We can use indirect ways of measuring an object Example - measuring angular diameter Diameter measured in degrees of an arc rather than in centimeters or kilometers

Moon’s Diameter Between 310 and 230 B.C. (2,200 years ago) Aristarchus published the diameter of the Moon. Used geometry and measurements during lunar eclipses and first and last quarter moons.

Angular Diameter Used to calculate diameters of objects in the solar system. Depends on the distance to the object and object’s diameter The closer the object, the larger its angular diameter

Two objects with different TRUE diameters can have the same ANGULAR diameter. Example - pencil and electrical pole

Similar Triangles Same angular diameter? Use similar triangles to determine true diameter Need to know true diameter of one object and the distance between the two objects

Corresponding angles are equal even if corresponding sides may not be Sides may not be equal but their ratios are!

Method you are going to use today we can use to measure the moon!! Save the materials because we will be doing this next week :)