When you project the Earth’s equator into space (the “ecliptic”), you will find that the Sun, and all the planets orbiting the Sun, are at a 23 some-odd degree incline to it. The Sun exactly crosses the equator twice a year, once on about March 21st (the Vernal Equinox, when spring begins), and once again on about September 21st (The Autumnal Equinox, when autumn begins). Additionally, the Sun is the most north of the equator on about June 21st (the Summer Solstice, when summer begins) and is the most south of the equator on about December 21st (the Winter Solstice, when winter begins).
Remember the basics: The Sun and all the planets move through a narrow band of stars called the Zodiac. That zodiac is at a roughly 23º incline to the Earth’s equator. Half of the zodiac signs are north of the equator. The other half are south of it.
Which ones?
It is hard to say exactly because the 23º tilt of the earth is not stable. It progresses to incline and decline through the aeons. In the Tropical Zodiac system, which aligns itself not to the stars but to the season, it is simple: The beginning of Aries through to the end of Virgo are north of the equator. The beginning of Libra through to the end of Pisces are south of it. The Summer Solstice occurs at the most northern point of the Tropical Zodiac: the beginning of Cancer. The Winter Solstice occurs at the most southern point: the beginning of Capricorn.
Therefore we use the tropical zodiac whenever we calculate declination.
“Declination” is a measurement of how far north or south of the equator a planet currently is. It’s pretty easy to tell just by knowing what sign a planet is in. A planet in Cancer will always be much more northerly than a planet in Capricorn, for example. But each planet also has a slightly unique tilt towards our equator. Knowing this would let you know which planet would have a higher northern declination if they were both near the same degree of the zodiac.
Declination is a (small) part of what makes a planet strong or weak. Different planets are strong at different points:
| Strongest | Weakest | |
| Moon & Saturn | Southern Declination - 0º Cancer |
Northern Declination - 0º Capricorn |
| Sun, Jupiter, Mars & Venus | Northern Declination - 0º Capricorn |
Southern Declination - 0º Cancer |
| Mercury | Souther or Northern - 0º Cancer or 0º Capricorn |
Equatorial - 0º Aries or 0º Libra |
