Inferior vs. Superior Planets
The five naked-eye planets can be divided into two groups based on
where they can be found in the night sky.
Inferior Planets -- Mercury and Venus
- The orbits of these planets lie INSIDE
the orbit of the Earth.
- From our perspective, they can never be seen separated very far from the Sun.
- The Earth can NEVER pass between one of these planets and the Sun.
- They will never be seen high in the sky at midnight.
- They show the full range of phases from new to full as they
(and the Earth) orbit the Sun.
- Visible against a dark sky only after dusk or before dawn
- They set shortly after the Sun if they are in the evening sky
- They rise shortly before the Sun if they are in the morning sky
- Superior planets -- Mars, Jupiter, and Saturn
- The orbits of these planets lie outside the orbit of the Earth.
- They can sometimes lie opposite the Sun from the Earth (that is, the Earth can be between them and the Sun).
- In this position, called opposition they will rise at
sunset, be high in the sky at midnight, and set at dawn.
- At this position they are at their closest point to the Earth.
- At other times superior planets can also be nearly in line with the Sun (conjunction) and
thus just as difficult to view as the Inferior planets.
- Because a superior planet never can pass between the Sun and the Earth,
superior planets are always seen at nearly full phase.
- They will never be seen as a crescent or new.
Revised September 28, 2009