Online Astronomy eText: Orbital Motions
Planetary Orbits
Diagram showing the orbits of the inner planets relative to each other, the Sun, and the orbit of Jupiter
The orbits of the inner planets. From the center out we have the Sun, Mercury, Venus and the Earth, then Mars and Jupiter. All the planets are orbiting in a counter-clockwise direction, as seen in this view from the North Ecliptic Polar direction. Note that Jupiter, Venus and the Earth have orbits which are nearly centered on the Sun, while Mercury and Mars' orbits are not centered on the Sun. Also, the inner planets' orbits are fairly evenly spaced, but there is a gigantic step outward from Mars to Jupiter.

Diagram showing the orbits of the outer planets relative to each other and the Sun
The "curtate" orbits of the outer planets (that is, as projected onto the Earth's orbital plane by looking southward from the direction of the North Ecliptic Pole). This projection makes the perihelion distance of Pluto look smaller than it is, because of the large tilt of its orbit; but it does still cross inside the orbit of Neptune near perihelion. The orbit of Comet Halley (P/1) is also shown. All the planets are orbiting the Sun in a counter-clockwise manner as viewed here, but Comet Halley is orbiting in the opposite direction, with retrograde revolution.

Diagram showing the orbits of Neptune and Pluto, showing Pluto's position in various years
The orbits of Neptune and Pluto, showing Pluto's position in various years. The orbit of Pluto has been rotated so that it lies in the same plane as Neptune's orbit. Where it appears to cross Neptune's orbit, it is actually hundreds of millions of miles above it.

Diagram comparing the orbit of Pluto to a circle of about the same size, offset from the Sun
A comparison of Pluto's orbit to a circle offset from the Sun. Even with an eccentricity of 25% the orbit of Pluto has a major axis less than 1.6% larger, and a minor axis less than 1.6% smaller, than a circle of the same overall size. Only very eccentric orbits such as those of comets are noticeably elongated.

Diagram of the orbits of Pluto and Neptune, showing how they are tilted relative to the orbit of the Earth
Relative to the Earth's orbit, both Pluto and Neptune's orbits are tilted upward on the right side of this diagram. For each planet the line of nodes (the line through the Sun where the planet's orbit intersects our orbit) is shown. Both ascending nodes (where the planet moves upwards through the orbital plane of the Earth) are at the bottom, but Pluto's orbit is tilted 17 degrees upward, and Neptune's less than 2 degrees. As a result Pluto's orbit is tilted upward by just over 15 degrees relative to Neptune's, along a line that would be nearly vertical in this diagram, putting Pluto nearly at its highest point relative to Neptune's orbit in the early 1980's.

Diagram showing the orbits of Pluto as seen from the 'side' of Neptune's orbit, so that orbit is shown as a horizontal line, and Pluto's orbit is shown as a tilted line
A side view of the orbits of Pluto and Neptune, showing the angle made by Pluto relative to Neptune's orbit (and the general plane of the Solar System), and how it places Pluto well above Neptune at perihelion and well below it at aphelion. See below for a similar view, but rotated 90 degrees clockwise about a vertical axis.

Diagram showing the orbit of Pluto relative to Neptune, as seen along the line of apsides (the line between its perihelion and aphelion points)
A side view of the orbit of Neptune along Pluto's line of apsides, showing Pluto's orbit extending above Neptune's at perihelion, below it at aphelion, and well to the side of it even where near the plane of Neptune's orbit. Dots represent the position of Pluto and Neptune in mid-2005. The vertical line represents the approximate position of the line of apsides, or the major axis of Pluto's orbit. Neptune can never run into Pluto, not only because the orbit of Pluto does not actually come close to intersecting that of Neptune, but also because Neptune's gravitational effects on Pluto's orbit have locked Pluto into a 3:2 resonance with Neptune, causing Neptune to always lap Pluto when it is on the aphelion side of its orbit, at least 1.5 billion miles beyond Neptune.

A view of the inner solar system on April 1, 2007, as seen from the North Ecliptic Pole (that is, looking southward towards the plane of the Solar System. Aside from the planets, the positions of asteroids on that date are also shown
Above, the inner solar system on April 1, 2007, as seen from the North Ecliptic Pole
Below, the inner solar system on that date as seen from the plane of the Ecliptic
Note that the asteroids are mostly relatively near the plane of the Ecliptic
A view of the inner solar system on April 1, 2007, as seen from outside the Solar System, looking toward the Sun in the plane of the Ecliptic. Aside from the planets, the positions of asteroids on that date are also shown.

A view of the outer solar system on April 1, 2007, as seen from above the plane of the Ecliptic. The positions of Kuiper Belt objects and comets are also shown.
Above, the outer solar system on April 1, 2007, as seen from the North Ecliptic Pole
Below, the outer solar system on that date as seen from the plane of the Ecliptic
A view of the outer solar system on April 1, 2007, as seen from outside the solar system, but in the plane of the Ecliptic. The positions of Kuiper Belt objects and comets are also shown.
In the "side" diagram of the outer solar system, note that Kuiper Belt objects lie mostly in or near the plane of the planetary system, as though they are an outer extension of that system; but comets are scattered all over the diagram, as if randomly scattered in space. For that reason, the comets are thought to be located in an extremely large, roughly spherical region referred to as the Oort Cloud, which has its origin in the early solar system, but has been filled with cometary bodies in an essentially random way due to gravitational interactions with passing stars (which were much closer to us when the solar system was young, and still in the cluster of stars in which it must have formed).

Diagram showing the outer solar system on April 1, 2007, as seen looking southward from the North Ecliptic Pole, including the orbits of some then-recently discovered Kuiper Belt objects, and comets Halley and Hale-Bopp
Above, the outermost solar system on April 1, 2007, as seen from the North Ecliptic Pole
Below, the outermost solar system on that date as seen from the plane of the Ecliptic
The diagrams include the orbits of a few Kuiper Belt objects, and two comets
Diagram showing the outer solar system on April 1, 2007, as seen in the plane of the Ecliptic, including the orbits of some then-recently discovered Kuiper Belt objects, and comets Halley and Hale-Bopp