The aspects of life that fall into the third house are often shortened to "communication". And that is not wrong but it is a bit hazy. Communication in what sense? In ancient astrology, the third house was called "The Joy of the Moon". So what is it about the Moon that is third-house-y?
The Moon is the fast-moving planetary body in the sky. In just 28 days is "visits" all degrees of the zodiac and it forms conjunctions with all planets. In doing so, it also carries the energies between them, it connects the large and wide 360 degree sky into a single milieu.
The movement of the Moon in the sky is the basis for the third house's association with neighborhoods, community life, gossip and communication. Planets in this house show how you transmit influences and communicate.
SUN
A person who has their Sun in the third house will have their identity and sense of self tied to their ability to learn and understand. What they value most is the ability to connect the dots, to get at least the basic outline of things, to have the larger picture more or less in place.
These people will be interested in a variety of topics, they will love to communicate with people from all walks of live. They will love to have some understanding of what everyone is doing. A strong interest in the media, journalism and reporting are suggested with this placement. Many so called media-junkies (people who are almost obsessed with following the news) have strong third house placements.
Third house Suns also love to connect people and with people. They are very rooted in community life, so if an opportunity arises for some community project, they are likely to express an interest and maybe even take the lead, especially if it something short-term. They don't like to feel tied down, they like movement and freedom so long-term commitments are not very appealing to them but short-term opportunities to check-up on the community are very welcome.
MOON
The Moon is at its home house here. People with natal Moon in the third house find comfort in learning new things. They find emotional soothing in knowing that the world is a big and interesting place. Each book, each new piece of information opens a new window to the world and that mental stimulation comforts them on an emotional level.
This is a house associated with communication and so having the Moon here creates the kind of person who can explain and intellectualize not only their own feelings but also the feelings of others. The intellectual angle on emotions might make others feel that this person is a bit emotionally detached and cold, a bit too rational at times. The third house is a place where a lot of movement around and change take place. The Moon itself is also associated with change and fast movement, so the overall result is a person who can be very changeable, unpredictable and whose life gets too hectic sometimes.
They also have a knack for mixing and matching different people and are very gifted at creating communities and brokering alliances.
MERCURY
Mercury is the planet of communication and information. When it is in the third house it gives the individual a sharp mind, curious disposition and love for learning. It fuels intellect and reason. Interest in a variety of topics is a given and one detail here is that these people will love to talk out all of their interests. A potential danger is that the individual may have a hard time slowing down his/her mind and focusing on the practical application of their ideas.
A busy mind that bores easily and loves life on the go. Eloquent speaker who is adept at choosing the right words, and mixing and matching different concepts. A talent for writing and public speaking is to be expected. Keeping up to date with the latest news and the latest gossip as well as great interest in social media and technology are also commonplace.
VENUS
Venus, the planet of diplomacy and arts, in the house of communication creates people with a talent for writing novels, plays, scripts, poetry, a talent for diplomacy and legal reasoning.
Venusian communication is characterized by beautiful words and balanced opinions. A style of interaction with the immediate environment that is marked by polite speech and desire for cooperation and partnership. Communication has to be beautiful, interactions with other people have to be balanced and diplomatic.
There is a bit of a risk with this placement that the person will expect others to follow a script to ensure that the exchange remains polite, balanced and pleasant, and very often the counterpart may not be aware that they are supposed to adhere to these unspoken rules.
When someone's approach to intellectual activities is colored by Venus, they look for beautifully written novels, balanced exposes without coarse language or overly intense debates. Love for reading and writing for fashion magazines and beauty blogs can also be suggested. Because of their gentle way of speaking, these people have great social success and are popular guests at gatherings and parties.
MARS
The planet Mars (think knives, lasers, fire) in the house of communication creates a sharp line delivery. Such people don't hold back, they have no filter and no patience for social graces or protocol because these stand in the way of them being true to themselves.
With Mars here inflammatory language is commonplace. These people love verbal sparring. A conversation is a game to be won. Arguments are welcome. Bullying is possible. Their words may feel like knives even when they like you and are trying to be nice. They don't have much patience for longer exposes so overly intellectual debates are not their forte. But quick, biting exchanges are.
On the bright side, people with this placement have no time and no interest in playing games and beating around bush. Mars does not understand the value of pretense in both senses - the positive and the negative. They don't understand the value of pretense as in politeness and diplomacy, and they also don't understand the value of pretense as in playing games. They do well with people who can handle inflammatory remarks and insensitive language. And even better, with people who value the information they receive regardless of the feeling with which this information is delivered.
JUPITER
Jupiter in the third house magnifies third-house themes. These people can be "know-it-alls" or they can really know it all. Education and learning is on special focus in their lives.
Wherever Jupiter goes that where we are being supremely supported and where we will be abundant in life. With this planet in the third house knowledge, travel, learning about far-away places and people is amplified. These people are skilled at putting facts together into a coherent theme, and putting pieces of knowledge together into a large well-argued exposes.
Many people with this placement are self-taught. Their love for freedom of exploration and the large number of topics they are interested in makes it hard for them to pick a major, and even if they do, they still continue to learn a lot about other things on their own.
Jupiter does not care for boundaries and that includes differentiation of knowledge areas. The danger is to become a jack of all trades - to know a little bit about everything but lack specialization in anything. Scattered knowledge and mental energies is a risk with this placement.
SATURN
The third house is light and fast-paced while Saturn is heavy and slow. It’s no coincidence that this house was called "The House of the Moon" (the Moon rules over Cancer, the sign opposite of Saturn-ruled Capricorn). Saturn is a synonym for mature, hard-working, sober energy and that energy is now in the house of learning and communication. Saturn will demand focus and methodological approach to learning.
In terms of destiny, people with this placement often experience events that make them feel like they can't connect with their immediate environment, like they don't belong. A gap between the individual and siblings or neighbors, or just difficulty in fitting into the community could be in suggested.
URANUS
Uranus is the planet of innovation, a planet which favors revolutionary approaches over time-tested traditions. This is the higher octave of Mercury. Uranus in the third house can produce some exceptional visionaries with unique progressive angles on contemporary issues and desire to create new ways and areas of learning.
In terms of destiny, many changes in elementary, middle and high-school can be suggested. Flips and turns with regard to what area subject matter they are interested in may be in the cards. Uranus likes freedom, it hates to be confined to a standardized curriculum . If this is taken to extreme, it can suggest scatteredness and inconsistency which is an energy already present in the third house. When you combine these two things together the risks are similar to those of Mercury in the third house - staying focused can be a challenge.
Interest in natural science or technology is not unusual for Uranus in the third people. They like formulating new theories and testing them, and they are rarely, if ever, discouraged from trying simply because other people think their ideas is outrageous.
Uranus pushes the boundaries of what has been done before, and it completely destroys the boundaries of what is conventionally accepted. These people often have to deal with people not understanding them, or, to be more precise, people not appreciating the novelty of their ideas.
NEPTUNE
Neptune in the third can play out in two ways. On one hand, Neptune is boundless water. It doesn't respect boundaries and limitations, it just flows everywhere and draws everything to itself. Neptune doesn't care about human-made divisions. It sees everything as part of the whole. In some way, we can see this as scatteredness because there is a lack of structure. This freedom of the mind and the intuition to roam the world and collect not pieces of data but impressions can create unmatched visionaries.
It can also work out the other way which is: it may not work out at all. Sometimes losing grip over your intellectual growth and failing to channel your mental and exploratory energy in some productive way can lead to waste of your potential. The third house is rational intelligence and is preoccupied with the material facts. Neptune doesn't have the same love for exactness. Sometimes words can be dreamy, can ring false or be too beautiful to be true. And that's just fine with Neptune.
Neptune is the higher octave of Venus. Communication is gentle and considerate of others. These people can be quite gifted in artistic expression. Interest in spirituality and applying their minds to spiritual pursuits can be expected.
PLUTO
People with Pluto in the third house look at communication through the prism of Plutonian energy. Read this as: power and control. Communication is exchange of information and information is power. Especially personal information. So in conversations these people tend to be quite reserved and careful about what they let on about themselves, all the while trying to pick up as much as possible from the other person.
If hurt, words can and will be weaponized. Manipulation will be employed as means of defense. Conversations are slow and careful so as to avoid situations where too much is revealed.
The third house also represents how we like to apply our rational faculties and with Pluto placed here, the person is likely to be very passionate about investigation and about understanding the world on a deeper level. They go all in in whatever picks their interest and leave no stone unturned. Psychology, psychoanalysis, mystery, crime, and the nature of power itself are typical areas of interest.