When you're first investigating your natal chart, you may quickly find that some of the houses in your natal chart are empty houses. An empty house in astrology means there are no natal planets located in that house. Many people worry that an empty house in astrology shows an area of life where they will struggle (like an empty 7th house of relationships means you'll never get married or an empty 10th house of career means you'll never have a career). But that's not true at all!
About Empty Houses:
There are only 10 planets in astrology while there are 12 houses, so every person has at least 2 empty houses (it's usually 3-5). This doesn't mean the energy of that house isn't present in your life. It actually means you're not as focused on it because it's not as much of a struggle!
There is belief that an empty house represents an area of life that you already dealt with in past lives, so there's not much karma to work out there. Houses that have planets in them are areas where we have to work out the energy, so we give them more focus because there's more to work on. This doesn't mean we neglect the empty houses in astrology!
When a house is empty, you're going to put more focus on the sign on the cusp, which is the very beginning of the house, and the ruler of the house (which is the natural planetary ruler for the sign on the house cusp, so if you have Aries on the cusp, Mars is the ruler of the house as ruler of Aries). The sign prevails over the energy of the house, and the ruler of the house often plays a bigger role.
So, let's say that Aries is on your 7th house cusp, and your 7th house is empty, and your natal Mars is in Pisces and the 6th house. You may find your work life (6th house) and relationships (7th house) to be intertwined, and you meet potential partners through your or their work.
Quick list of planetary rulers:
Aries - Mars
Taurus, Libra - Venus
Gemini, Virgo - Mercury
Cancer - Moon
Leo - Sun
Scorpio - Pluto
Sagittarius - Jupiter
Capricorn - Saturn
Aquarius - Uranus
Pisces - Neptune
Note that if Chiron or the Lunar Nodes fall in an empty house, then there is some work to be done, with wounds and healing for Chiron, and with finding your path and purpose with the Lunar Nodes.
The Empty Houses in Astrology:
There are additional articles outlining the houses in astrology that you may want to check out for more about the energy and what the house rules if it's an empty house in your natal chart (the energy of the house and whatever it rules if it's empty can be easier for you):
All About the First House in Astrology
All About the Second House in Astrology
All About the Third House in Astrology
All About the Fourth House in Astrology
All About the Fifth House in Astrology
All About the Sixth House in Astrology
All About the Seventh House in Astrology
All About the Eighth House in Astrology
All About the Ninth House in Astrology
All About the Tenth House in Astrology
All About the Eleventh House in Astrology
All About the Twelfth House in Astrology
Suggested Reading: Intro to Astrology Houses; there are also 2 articles focusing on groups of empty houses, one on the empty relationship houses (5th, 7th, and 11th houses) and one on the empty professional houses (2nd, 6th, and 10th houses)