The image below shows retrograde motion, or when a planet travels backwards relative to the fixed stars. (Picture down below)
• prograde, sideways
• prograde, backwards
• retrograde, forwards
• retrograde, backwards
2. Why was stellar parallax NOT observed by ancient astronomers?
• ancient astronomers were more interested in observing planets and stars
• ancient astronomers were looking at the wrong stars
• stellar parallax is too small to observe without powerful telescopes
• they cannot tell the difference between the stars and the planets
The image below shows fixed stars.
Motion, or when a planet travels
Relative to the
Planet's orbit
Earth's orbit
Sun