Void-of-course Moon, August 1984

Where the void-of-course idea comes from

The phrase "void of course" belongs to traditional horary astrology. William Lilly, writing in 1647, described the Moon as void when she has separated from one planet and will not reach another aspect while she remains in her sign, and he warned that matters then "go hardly on". He also noted exceptions: the Moon was thought to perform somewhat better when void in Taurus, Cancer, Sagittarius or Pisces. Earlier Hellenistic authors used a related term, kenodromia, "running in the void", which was usually judged by whether the Moon would complete an aspect within the next 30 degrees, regardless of sign boundaries.

The sign-based version became the standard in the twentieth century, and modern astrologers extended it to Uranus, Neptune and Pluto. Today two definitions sit side by side: the modern one, which counts aspects to all planets from the Sun to Pluto, and the traditional one, which counts only the seven visible bodies up to Saturn. Because fewer planets are available, the traditional definition tends to start the void earlier and so produces longer periods.

How the void periods are calculated

The Moon changes sign about every 2.25 to 2.5 days, so there are roughly a dozen void periods a month. For each stay in a sign the site finds the moment of the Moon's last exact conjunction, sextile, square, trine or opposition to a planet, and then the moment it enters the next sign. The time between the two is the void period, listed with its start, end, duration and the planet and the aspect that started it (the Moon's last aspect in the sign). Periods can last a few minutes or well over a day; a long one usually means the Moon's last aspect came early in the sign. Occasionally the Moon makes no aspect at all in a sign, and the page notes that instead of a last aspect.

The page also offers a choice between geocentric and topocentric mode. Geocentric positions are measured from Earth's centre, which is the default. Topocentric mode measures from your reference location. The Moon is so close that its position as seen from the surface can differ by up to about a degree, and since it moves roughly half a degree an hour, the start or end of a void period can move by as much as two hours. If you use topocentric mode, make sure the reference location is the place where the action will actually happen.

Using void-of-course times in practice

Look at the month view before scheduling something you want to go somewhere: a launch, a signature, an application, a first meeting. If it falls inside a void period, moving it by a few hours is often enough. The list can be added to a digital calendar, a single period or a whole month at a time, so the warning appears where you plan. If you want a date that also weighs the Ascendant, Mercury and the house of the matter, not just the Moon, the AI electional astrology advisor Bonatti scans your chosen range for you.

Void periods are well suited to routine, follow-up work, reflection, rest and finishing what is already underway. Many astrologers also note that decisions made during a void Moon tend to be revisited later, which is not always a bad thing. Treat the void Moon as a timing preference, not a ban: the world keeps working during those hours, and a void period in the middle of the night rarely matters to anyone.