When you think of planets, you probably think back to your school days and the models of the solar system you carefully painted. You may also think about rockets and spaceships and missions to Mars, or perhaps you’ve looked through a telescope to wonder at our far distant neighbors and their mysteries.

In astrology, however, we have a close relationship with the planets. Far from being distant balls of ice, rock or gas, the astrological planets have an influence which is up close and personal, and which pervades every aspect of our lives. Read on to find out more about the planets in astrology – what they are, what we use them for, what they do and why they’re the basic building blocks of your birth chart.

What are the Planets in Astrology?

The planets used by astrology are the very same planets you learned about in school: Mercury, Venus, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto.

To that list, we add the Sun and the Moon. The Sun and the Moon are not planets – the Sun is a star, and the Moon is, well, a Moon or really, a satellite to our Earth. Technically in astrology we call the Sun and the Moon “luminaries” or givers of light, but they are treated in the same astrological fashion as a planet, and you’ll often hear astrologers calling the Sun and the Moon planets just for ease of reference. Don’t lose any sleep over it.

In astrology, the Sun, Moon, Mercury, Venus and Mars are sometimes grouped together with the term “personal planets or inner planets”. These planets are considered to provide a cohesive view of your basic personality, motivations and drives. These planets move relatively quickly around the Sun, and so are useful for daily and weekly predictions.

The others, Jupiter, Saturn, Uranus, Neptune and Pluto, are called the “outer planets”. These planets are much more slow-moving in our solar system, sometimes spending years in a single zodiac sign. If personalized in a chart (more on this later) they can be extremely important on a personal level, but they are also important for looking at long term life trends.

In Astrology, How do the Planets Work?

The planets are the core building blocks of any birth chart. At the time and place of your birth, every planet is somewhere in the celestial sphere – in a particular zodiac sign and in a particular house of your chart. Your birth chart is essentially a map of the heavens at the time you were born, containing the position of all of the planets and showing the angles and connections they make to one another.

Astrologically, each and every planet is said to embody a particular energy. This energy is expressed or channeled in a particular way, via the zodiac sign where that planet is. The energy is also directed towards a particular area of your life, shown by the astrological house the planet is in.

A rough and ready guide to planetary energies would look something like this:

The Sun: Willpower, lifeforce, vitality, health, ego
The Moon: Emotions, feelings, instinctive reactions
Mercury: Communication, intellect, logic
Venus: Love, magnetism, values
Mars: Drive, ambition, desire, anger
Jupiter: Philosophy, expansion, belief
Saturn: Responsibility, limitation, control
Uranus: Individuality, freedom, independence
Neptune: Spirituality, illusion, compassion
Pluto: Regeneration, transformation, rebirth

In your natal chart, Mars in Scorpio in your 10th house might express itself with your drive and ambition (Mars) being passionately expressed (Scorpio) in your career (10th house). In other words, you’d be pretty ruthless in your ambitions and personally driven to succeed at all costs. On the other hand, Mars in Gemini in the 11th house might find you giving your all to writing letters, making speeches and campaigning to save the world – your drive and ambition (Mars) being communicatively expressed (Gemini) in the community (11th house).

So, you can see that the same planet can and will express its energy very differently according to where in your birth chart it is.

Planets will also often form particular angles to other planets; when this happens, it’s called planets being in aspect, the planets modify one another’s energy in a variety of different ways, further complicating the picture.

Away from your birth chart, the planets are also vitally important in predictive astrology. Your natal chart is a static map of how things were when you were born, but the planets are of course still moving. As they move, they form aspects to their original birth positions, to other planets in your natal chart, and to one another’s current positions. These are called transits and are a very common predictive tool in astrology. Transits can tell us what is going on around us today, next week, next month, next year – they don’t compel us to act, as we retain free will, but transits can advise us how best to make use of upcoming planetary energies.

Sometimes, as seen from earth, a planet will appear to be moving backwards. This is called retrograde motion; you’ve probably heard of Mercury retrograde, but the other planets do it too. During retrograde motion, the planetary energy is in some ways reversed, so it’s important to interpret retrogrades carefully.

In Astrology, Which Planet is Most Important?

The answer to that depends entirely on your own birth chart – there are a variety of complex considerations when judging which planet is strongest for any individual.

The chart ruler is always an important planet. This is the planet which rules your Ascendant sign – the sign rising on the Eastern horizon at the time and place of your birth.

The planetary rulerships are as follows:

Aries – ruled by Mars
Taurus – ruled by Venus
Gemini – ruled by Mercury
Cancer – ruled by the Moon
Leo – ruled by the Sun
Virgo – ruled by Mercury
Libra – ruled by Venus
Scorpio – ruled by Pluto and Mars
Sagittarius – ruled by Jupiter
Capricorn – ruled by Saturn
Aquarius – ruled by Uranus and Saturn
Pisces – ruled by Neptune and Jupiter

So, if your Ascendant sign is Pisces, then we would consider Neptune to be the chart ruler; if your Ascendant is Aries then Mars is the chart ruler and so on.

Another way of judging a planet’s relative importance in the natal chart is whether or not it resides in domicile, that is in its natural home. Referring to the list of rulerships, we can see that Venus, for example, is in domicile in Taurus or in Libra – so if your natal chart shows Venus in either Taurus or Libra, that strengthens Venus’ importance in your chart.

Astrologers also look to see if any of the planets are conjunct (very close to) important chart points like the Ascendant or the Midheaven, or whether any major aspect patterns are formed across the chart as a whole; if there are any, then the planets involved in these will take on extra importance in the chart.

Astrology is a complex blend of hundreds of complementary but often contradictory energies and messages within the chart. Sun signs and horoscopes are great fun, but to really understand what’s going on in your natal chart, and to put astrology to its proper use, you need to be able to understand what each of the planets is up to in the birth chart, and what it’s doing now too.