Celestial bodies can stand in the sky in different ways to each other. This relationship is considered on the basis of their relationship to the earth and the sun. In that case, we distinct between conjunction and opposition.
What is the conjunction?
The conjunction can also be described as an encounter of two planets or a planet with the sun or the moon. Seen from Earth, the other two celestial bodies seem to be in almost the same position. A planet stands in conjunction if it is located in the same ecliptic length as the sun, the elongation is then 0°. In the conjunction, it seems that a planet seen from Earth is directly behind or in front of the Sun.
What is the opposition?
Talking about the opposition, we include those planets that are further away from the Sun than the Earth. This relationship refers to the event when the sun, earth and corresponding planet are in one single row, but the earth appears to be in the middle of the other two celestial bodies. As a result, the planet in the sky is exactly opposite the Earth. Thus it sets down when the sun rises and vice versa. The opposition is therefore the opposite of the conjunction.
Upper and lower conjunction
With the inner planets (Mercury and Venus) no opposition can occur, instead we speak of upper and lower conjunction. If they are behind the Sun when seen from Earth, they are in the upper conjunction, if they are between the Sun and Earth, they are in the lower conjunction.