Longitude and latitude

Longitude and latitude are pretty plain concepts. They are used to locate places on the surface of the Earth. The reference for longitudes is Greenwich. A longitude measures how far East-West a place is from Greenwich. The maximum longitude is therefore 180 degrees.

The reference for latitudes is the equator. A latitude measures how far North/South a place is from the equator. The maximum latitude (that of the poles) is therefore 90 degrees.

Longitudes and latitudes are commonly expressed in degrees. However, longitudes can also be expressed in hours (dividing the Earth into 24 hours instead of 360 degrees). This is important to remember when reading astrology books, because when charts were calculated by hand instead of by computers, it was more convenient to use longitudes expressed in hours. You will therefore find a lot of longitudes in hours in the astrological literature. Nowadays, since these calculations are more or less obsolete, and since all atlases use degrees, not hours, we may as well forget about longitudes in hours, and use only degrees.

For example the coordinates 175E39' and 40S58', describe a place 175 degrees and 39 minutes east of Greenwich, and 40 degrees, 58 minutes south of the equator – on the opposite side of the globe and in the southern hemisphere.

Celestial longitude and latitude

There is, however, another use of the words longitude and latitude in astrology and astronomy, which refers not to the Earth but to the celestial sphere. This is not used to locate places on Earth, but planets or stars in the sky. In this different context, the longitude measures how far a planet is from 0° Aries (tropical), and the latitude measures how far the planet is from the ecliptic. So do not get confused! Sometimes the words longitude and latitude refer to a city, and sometimes they refer to a position in the heavenly sphere.

Midheaven

The Midheaven is also called the MC.

Suppose, on a particular day, the Sun rises at 5:30 AM, and sets at 7:30 PM. Just halfway between the two, at 12:30 PM, the Sun reaches its highest point. At that particular time, the Sun is exactly on the Midheaven.

Hence the term 'Mid-heaven', meaning half way along the visible part of the ecliptic.

Midheaven (MC) and local meridian

A meridian is simply a line that goes from the North Pole to the South Pole. Imagine the Earth as a pumpkin – the lines are the meridians. On a map, the meridians are the vertical lines. One could also call the meridians 'longitude lines', because all places on a meridian have the same longitude.

From there, can you guess what the local meridian is? The line that goes from the North Pole the South Pole via yourself.

Now let us make a leap and understand what the Midheaven (also called MC, or cusp of the 10th house) is. Let us suppose you are standing somewhere in Auckland. There are certain stars above your head. Suppose, at the same moment, another person is standing somewhere in Milan. There are other stars above their head. Similarly, each local meridian can be projected onto the celestial sphere, and will intersect different stars. The Midheaven measures where the point on top of your head projects onto the zodiac.

Said in more elegant terms, the Midheaven, or MC, is the projection of the local meridian on the zodiac. (You could also say, the projection of the local meridian on the ecliptic, since the ecliptic is the line in the middle of the zodiacal band.)

In other words, the Midheaven is a local vertical line projected onto the zodiac.

So this is the way to remember what the Midheaven is. Think of the meridian (a line going from the South Pole to the North Pole) passing just on top of your head. Project this high in the sky, into the celestial sphere.

The intersection of this meridian with the line of the zodiac is the Midheaven.

You can immediately make a deduction: all the points which stand at the same longitude must have the same Midheaven, since they are all located on the same local meridian. This is true. Verify it for yourself. Take any chart in Clairvision Virtual Astrologer, make a listing, and note the MC. Then edit the chart: change the latitude. For instance, if it was a southern latitude, make it a northern one. Now you have the chart of a place with the same longitude, but a different latitude. Press OK, make another listing – same MC. Edit the chart again, this time making the latitude = 0. Try another listing – same MC!

(If this is not too clear, go through the chapter on the celestial sphere first, and then come back here for another go.)

Midheaven versus zenith

Zenith is an astronomical term which is not used in astrology. Let us introduce it here, however, so as to better understand the concept of Midheaven.

The zenith is the point where a local vertical line intersects the celestial sphere.

In other words, whenever you are standing somewhere, the zenith is that point of the celestial sphere which is right above your head.

The zenith is not the Midheaven. The zenith can be located in any part of the celestial sphere, while the Midheaven can only be on the ecliptic (the ecliptic being the line in the middle of the band of the zodiac). Roughly speaking, the Midheaven is a projection of the zenith onto the zodiac.

The only case where the zenith and the Midheaven would be identical would be if you were located somewhere not far from the equator, with the ecliptic right above your head.

Conversely, the closer you are from the North or South Pole, the greater the difference between the zenith and the Midheaven. Close to one of the poles, the ecliptic (and therefore the Midheaven, which is a point on the ecliptic) is not far from the horizon.

Note: the point which is exactly opposite the zenith, that is, the point of the celestial sphere right under your feet, is called the Nadir.

Imum Coeli

Having understood the Midheaven (MC), it is easy to figure out what the IC is: exactly the opposite. The Midheaven measures where the point above your head intersects the zodiac. The IC measures where the point right below your feet (going through the Earth) intersects the zodiac.

Expectedly, on the zodiac, there are 180 degrees between the MC and the IC.

Just as the MC is the cusp (beginning) of the 10th house, so the IC is the cusp of the 4th house.

Ascendant and Descendant

Before reading this section, make sure you have understood Midheaven and local meridian (MC).

Imagine you are watching the sunrise. As we saw before, the Midheaven is related to the point just above your head. The Ascendant is the projection onto the zodiac of the point where you see the Sun rise.

Imagine you are watching the sunset. The Descendant is the projection of the point where you see the Sun set onto the zodiac.

So the Ascendant is on the eastern side of the horizon, and the Descendant is on the western side of the horizon.

At any time of the day or night, some stars are rising, others are setting. The projection onto the zodiac of the point where stars are rising is the Ascendant. That of the point where stars are setting is the Descendant.

In astrology, the Ascendant marks the beginning of the 1st house. The Descendant marks the beginning of the 7th house.

Astrology fundamentals – sky movements in a day

When designing Clairvision Virtual Astrologer, one major purpose was to help astrologers understand the movements of the zodiac – how it turns!

In Clairvision Virtual Astrologer you can use the Animation feature to view planet movements with various time increments. Keep moving the chart forward by one hour and you will see how the house cusps and the planets move during a 24 hour period. Keep moving until you see the Sun setting, then midnight (when the Sun is close to the Imum Coeli), then sunrise.

Ponder on these movements. Try to relate them to your observation of the sky, of the Sun, Moon and planets. The more you can see how celestial movements translate into the chart, the more you will become a knower of the art.

Vertex

The vertex was introduced by modern astrologers.

Astronomically, at any given moment, the vertex is the point of the ecliptic which is due west. (In more technical terms, the vertex is the intersection of the prime vertical and the ecliptic.)

Astrologically, the vertex is said to tell about the way an individual relates to others.

Note: vertex and Descendant. As the Sun sets in the west, you may wonder what difference there is between vertex and Descendant. As you know, the Sun's course changes during the year. In winter, the arc described by the path of the Sun is shorter than in summer; and so the points of sunrise and sunset move a little bit every day. Therefore, saying that the Sun rises in the east and sets in the west is only approximately true. The Descendant is roughly due west, but not exactly.

The vertex, on the other hand, is that point of the ecliptic which corresponds exactly to the west.

In Clairvision Virtual Astrologer, the longitude of the Vertex can be found in the 'Detailed Listings' under the 'View' menu.

East point, or equatorial Ascendant

In Clairvision Virtual Astrologer, Vertex and East Point can be found in the 'Detailed Listings'.

Like the vertex, the east point is an invention of 20th century astrologers.

Astronomically, it is the point of the ecliptic that would be the Ascendant if the chart was calculated for the same time and longitude, but for latitude = 0 (that is, on the equator). Hence the name 'equatorial Ascendant', also given to the east point.

In Clairvision Virtual Astrologer, the East Point position is in 'Detailed Listings' (click on 'View', 'Listing', 'Detailed').