Heliocentric
Heliocentric measures every direction from the centre of the Sun.
This is not an adjustment to the Earth-based settings but a different vantage point altogether, and the first thing it changes is not a position. It changes which bodies there are to position at all.
The chart's contents change
In the heliocentric frame the list of available bodies is rebuilt, because three of the usual ones stop making sense and one new one appears.
| Body | Geocentric | Heliocentric |
|---|---|---|
| The Sun | yes | no |
| The Earth | no | yes |
| The Moon | yes | no |
| The lunar nodes and apogee | yes | no |
| Mercury to Pluto | yes | yes |
The Sun goes. The origin is now at its centre, and a body has no direction from its own centre, so a heliocentric solar position is not a number that exists.
The Earth arrives. From the Sun, the Earth is the third planet out, and it has a position like any other. It is always exactly opposite where the Sun appears from here: the same line, read from the other end.
The Moon goes, and the nodes with it. The Moon orbits the Earth, not the Sun. Its heliocentric position would be the Earth's position with a small monthly wobble on it, which adds nothing to the Earth's own. The lunar nodes and apogee are features of the Moon's orbit around the Earth and are meaningless without it.
This is why changing the origin can empty a selection of bodies. The choices are not being discarded; the bodies chosen do not exist in the frame the origin has moved to.
What the positions mean
A heliocentric position is a planet's actual place in its orbit.
That is a stronger statement than it sounds. Geocentric positions are compounded of two motions — the planet's own orbit and the Earth's — mixed together by the fact that the observer is riding on one of them. Heliocentric positions have the Earth's motion removed, because the Earth is no longer where you are standing.
The consequences show at once:
- Motion is smooth and steady. Each planet moves round its orbit at a rate that varies only gently. There are no stops, no reversals, no loops.
- Speeds are simply orbital periods. Mercury goes round in 88 days and Neptune in 165 years.
- The bodies stay much closer to the ecliptic. Seen from the Sun, a planet's distance from the ecliptic plane is just its orbital inclination — small and slowly varying — rather than the larger swings that the Earth's own motion introduces.
Nothing is retrograde here
The clearest consequence has its own page next, but it belongs here as well: no planet is ever retrograde in a heliocentric frame.
Retrograde motion is not rare or small in this frame; it does not occur. That is why a calculation whose subject is retrograde motion has nothing to work with here: what it looks for is a geocentric phenomenon.
What it is for
Heliocentric work is a minority practice and this site takes no view on its interpretation. What can be said is what it shows:
Real orbital relationships. When two planets are on the same side of the Sun, or on opposite sides of it, the heliocentric frame shows it directly and the geocentric frame does not.
Cycles without the Earth's interference. A heliocentric aspect between two outer planets is a clean statement about their orbits. The geocentric version of the same aspect is smeared by the Earth's annual motion and the retrograde loops that come with it.
A check on what is real. If a pattern appears geocentrically and vanishes heliocentrically, it reflects the vantage point rather than the planets, which is useful to know either way.
What comes next
The next page takes up retrograde motion, the clearest example of a geocentric appearance that is not a fact about the planet itself.