The transit of Venus

A transit of Venus is the passage of Venus in front of the solar disc, as seen from the Earth. It is one of the rarest predictable astronomical events there is — and the reason for its rarity is the same reason that makes it astrologically interesting.

Why it is so rare

Venus comes between the Earth and the Sun about every 584 days. Most of the time it passes above or below the solar disc, because its orbit is inclined a little over three degrees to the Earth's.

A transit requires the inferior conjunction to fall exactly when Venus is passing through one of the two nodes of its orbit. The result is a peculiar rhythm: two transits eight years apart, then a pause of 121.5 years, another pair eight years apart, then 105.5 years of pause. The full cycle lasts 243 years.

The most recent pairs fell in 1874/1882 and 2004/2012. The next transit takes place in 2117 — no one alive today will see it.

Why it mattered historically

For a reason that has nothing to do with astrology and belongs here all the same: the transits of the eighteenth century provided the first usable measurement of the distance between the Earth and the Sun. Observers travelled halfway around the world for them — one of the first international research ventures of any kind.

The scale of the solar system, in other words, was established from a transit of Venus.

And astrologically?

Restraint is in order here, and for a technical reason.

Classical astrology has no separate interpretation for a transit. What it does have is the inferior conjunction of Venus and the Sun — and that happens every eighteen months, whether Venus passes in front of the disc or beside it. Astrologically a transit is an inferior conjunction of unusually small latitude; reckoned in degrees of longitude, and that is how astrology reckons, it is no different from the rest.

Interpreting it as an “event of the century” therefore rests on a criterion — latitude — that plays no part in the rest of astrological practice. Anyone who wants to give the transit a special interpretation should say why latitude counts here and not elsewhere.

What can be defended

The inferior conjunction itself has a clear meaning in the tradition: Venus is combust, that is, overwhelmed in its effect, and at the same time it shifts from evening to morning visibility. A change of visibility phase is a recognised criterion — a good deal older and better founded than anything said about the transit as such.

See also: the planets and their condition, retrograde planets — Venus is retrograde during a transit.