Ten Treatises on Astronomy (Book of Astronomy)

...tation of heat: and no other sign is so close to the nature of the sun as Leo: because although Aries and Sagittarius are fiery signs: nevertheless the strength of the sun's heat does not appear so clearly; nor is the light so bright or so subtle as it is in Leo. And Albumasar Abu Ma'shar (787–886), one of the most influential Persian astrologers in the Middle Ages. said that the sun and Leo agree in this, namely that the sun is in the middle of the planets: and Leo is in the middle of summer: because the heat of summer is at its ultimate and strongest when the sun is in Leo.

Why Cancer is the house of the Moon.

Cancer truly was assigned only to the Moon for a house, which is the nocturnal light-bearer original: "luminare nocturnum"; medieval astronomy called the Sun and Moon the two "lights.". This is because Cancer is the first moveable sign from the beginning of the signs which agrees with the moon in femininity, mobility, coldness, and humidity. And it is the house closest to the house of the light-bearer from which the moon receives light, more than any other moveable or cold or humid sign that agrees with the nature of the moon. And the moon is also called the "light" of the sun because she receives light from him: and those two houses Leo (Sun) and Cancer (Moon). are brighter and more splendid and more in agreement with the natures of the light-bearers than any of the other houses in all climates and in all regions of the world.

Why Capricorn and Aquarius are the houses of Saturn.

And just as the Sun and Moon are the brighter and more splendid and more luminous bodies than the other super-celestial bodies: and their light is perceived more clearly and more manifestly than the light of any of the others: and they are "fortunes" that increase: so the obscurity and darkness of Saturn is perceived beyond the other obscurities and darknesses of the other super-celestial bodies: and he is the worst of all misfortunes original: "infortuniis"; in astrology, Saturn was the "Greater Malefic," associated with hardship and decay. and is destructive. Hence, since light and splendor are directly contrary to obscurity and darkness, and vice versa: and the light-bearers signify splendors and light and clarity, and Saturn signifies obscurity and darkness: for this reason their houses were opposite in a direct line. And this was the reason why Capricorn and Aquarius were assigned to Saturn for his houses. And similarly Capricorn and Aquarius are dark houses so that when the sun is in them, the air is then more obscure and more removed from purity: and especially when it is in Aquarius because then is the peak and ultimate of winter's cold.

Why Sagittarius and Pisces are the houses of Jupiter.

Sagittarius and Pisces were assigned to Jupiter for his houses next to the houses of Saturn because Jupiter succeeds Saturn in the order of the circles The planetary spheres, ordered by distance from Earth. immediately and is a strong fortune so that he breaks the malice of Saturn: and those two signs behold the houses of the light-bearers from a trine aspect An angle of 120 degrees, considered the most harmonious relationship in astrology. which is the aspect of complete and perfect friendship, just as opposition is the aspect of ultimate enmity. And because he is a fortune beyond the other fortunes (except the light-bearers): it was necessary that his houses be designated in such places that they behold the houses of the light-bearers with an aspect of love beyond the other aspects. For Pisces beholds Cancer, which is the house of the nocturnal light-bearer, from a trine aspect and is of its own triplicity The grouping of three signs by element; both Pisces and Cancer are Water signs. which also increases the goodness of the aspect. And Sagittarius similarly beholds Leo, which is the house of the diurnal light-bearer, from a trine aspect and is of its own triplicity Both Sagittarius and Leo are Fire signs..

Why Aries and Scorpio are the houses of Mars.

Aries and Scorpio were assigned to Mars for his houses next to the houses of Jupiter: since Mars succeeds Jupiter in the order of the circles immediately and is evil and unfortunate—his misfortune and his evil are less than the misfortune and malice of Saturn. And those two signs behold the houses of the light-bearers from a square aspect original: "quarto aspectu"; a 90-degree angle, considered a relationship of tension or conflict. which is the aspect of moderate enmity. And because he is an evil beneath Saturn (who signifies ultimate malice): it was necessary

that his houses be designated in such places that they behold the houses of the light-bearers with an aspect of moderate enmity. For Aries beholds Cancer, which is the house of the nocturnal light-bearer, from a square aspect, nor is it of its own triplicity, which also makes the aspect worse. Scorpio similarly beholds Leo from a square aspect, which is the house of the diurnal light-bearer.

Why Taurus and Libra are the houses of Venus.

Taurus and Libra were assigned to Venus for her houses next to the houses of Mars because she follows the sun in the order of circles to which her own house is assigned. And for this reason, the houses of Venus follow the houses of Mars. And Venus is a good fortune: but she is not as perfect a fortune as Jupiter: because Jupiter is such a strong fortune that he breaks all the malice of the malicious, which Venus cannot do: yet although she cannot break the malices of others as Jupiter does, she nevertheless diminishes them as she can and by herself brings fortune and good. And her fortune and goodness is beneath the fortune and goodness of Jupiter. And those two signs behold the houses of the light-bearers from a sextile aspect A 60-degree angle, considered a friendly but less powerful relationship than a trine. which is the aspect of moderate friendship. And because she is a good fortune beneath Jupiter (who signifies perfect and ultimate goodness and friendship): it was necessary that her houses be designated in such places that they behold the houses of the light-bearers with an aspect of moderate friendship. For Taurus beholds Cancer, which is the house of the nocturnal light-bearer, with a sextile aspect, which is the aspect of moderate friendship, although it is not of its own triplicity. Libra beholds Leo from a sextile aspect, which is the house of the diurnal light-bearer.

Why Gemini and Virgo are the houses of Mercury.

Gemini and Virgo were assigned to Mercury for his houses next to the house of Venus: because he follows Venus in the order of the circles: and he is "mixed" Mercury was considered neutral, taking on the qualities of the planets it is near.: yet in his nature he is more fortune than misfortune: but he turns toward the nature of that to which he is joined. And this is the reason why he is called "mixed." Namely, that the houses do not behold the houses of the light-bearers by any aspect because they are similarly adjacent to them. And because Mercury is not so far removed from the sun that he can be in any aspect with it Mercury is always close to the Sun in the sky, so it cannot form major angles like 60, 90, or 120 degrees from it.. But you might say that Gemini beholds Leo and Virgo beholds Cancer: however, that does not have a place in such a case: because according to this consideration no sign is said to "behold" the house of any light-bearer from any aspect if the house of the other light-bearer falls within those boundaries. Hence, Gemini is not said to behold Leo because Cancer (the house of the moon) falls within those boundaries; nor is Virgo said to behold Cancer: because Leo (the house of the sun) falls within those boundaries. And understand the same regarding other signs: that Aries does not behold Leo in a trine aspect because of Cancer (the house of the moon) which falls within those boundaries which it [Aries] beholds in a square aspect. Scorpio does not behold Cancer in a trine aspect because of Leo (the house of the sun) which falls within other boundaries which it [Scorpio] beholds in a square aspect. Taurus does not behold Leo in a square aspect because of Cancer (the house of the moon) which falls within those boundaries which it [Taurus] beholds in a sextile aspect. Libra does not behold Cancer in a square aspect because of Leo (the house of the sun) which falls between those boundaries which it [Libra] beholds in a sextile aspect. All these things are considered under the reasoning of why the signs were assigned to the planets for houses. It is different, however, for planets existing in those signs, as is fully seen in the chapter on the aspects of the planets. Many other causes and opinions of philosophers could be assigned, but to avoid being too long-winded, let the above-mentioned reasoning suffice for you.