Answer: Look at or examine the Sun.
Explanation: Helioscope is a device that is used to observe the sun. The term "heliocentrism" refers to the idea that the sun is at the center of the solar system. The Greek god Helios is the personification of the sun in ancient Greek mythology. So, it is likely that a helioscope was used to look at or examine the sun, rather than measure the distance between planets, search the surface of the Moon or plot out a planet's orbital path.