MC in Polar Regions

Historically, astrology has been developed mainly in temperate latitudes, and therefore the mathematical problems that occur in polar regions have not received much attention in astrological texts. As a result, many modern astrology programs have failed to deal with these issues in a consistent manner.

The crux of the problem is that the normal (temperate latitude) way of defining chart angles and houses breaks down in polar regions. In these latitudes, it becomes possible for the Ascendant to retrograde, and for certain portions of the zodiac never to rise at all.

Generally, except in some very specific polar locations, it is always possible to identify the Ascendant as that part of the zodiac that is rising across the horizon (even though it may in fact be retrograding), and this happens to occur always in the Eastern horizon.

However, there are two different ways of determining the Midheaven (MC), which sometimes give diametrically opposed answers for its position in the zodiac.

•Always towards equator – In this case the MC is defined as the intersection of the prime meridian with the ecliptic, towards the equator (or more precisely the ecliptic). This means that the MC is always due south in northern polar regions (and conversely is due north in southern polar regions), even though, on those days when the Sun does not rise, the MC also remains below the horizon. Another consequence of this definition is that the MC is the same for any location along a line of longitude, right from one pole to the other.

•Always above horizon – In this case the MC is defined as the intersection of the prime meridian with the ecliptic, above the horizon. This means that the MC is always above the horizon (even when the Sun does not rise during the day), but as a consequence, the position of the MC in the zodiac jumps by 180 degrees (i.e. has a discontinuity) as you move along a line of longitude from the equator to the winter pole.

When this option is changed in the "Preferences" dialog, "Calculations" tab, any charts that are subsequently opened or calculated will use the newly selected calculation method, but charts that have already been calculated retain the option that was in effect when they were calculated.