apparent brightness apparent motion size location
I am hesitating between 4 options to answer the following question, which option should I choose?
Question: In the 17th century, to estimate the distance to other planets, scientists first used the technique of viewing the planet from two different locations on Earth's surface. Which characteristic of the planet were the scientists using to calculate the distance from Earth?
Possibilities:
- apparent brightness
- apparent motion
- size
- location

location