The orbits of both of these planets are inside the earth's own orbit which is why they are often referred to as inner planets. All other planets in our solar system have orbits outside the earth's because they are farther away from the sun. When they form a conjunction with the sun (i.e. are located at the same degree of the zodiac) they can be located either between the sun and the earth, which is known as an inferior conjunction; or behind the sun, which is known as a superior conjunction.
From a horoscope it is possible to tell which is the case. An inferior conjunction can only be formed when either Mercury or Venus are retrograde at the time of the conjunction with the sun, otherwise the conjunction will be a superior one.
- Visualizing Retrograde Motion of Planets (Video David Cochrane, 2015; 20 min)
- The Four Faces of Mercury (Michael R. Meyer, 2000; khaldea.com)
Notes and References
- Illustration from Michael Erlewine