Planets in a birth chart do not act alone. When two of them sit at certain angles to each other, astrologers say they form an aspect, and those two parts of your personality are wired together. Some aspects make the connection easy, some create friction, and some fuse the two planets into one force. Aspects are often what make a chart feel specific: two people can share a Sun sign, yet one has that Sun sitting at a tense angle to Saturn and the other has it flowing with Jupiter, and they will describe very different lives.
The zodiac is a circle of 360 degrees. An aspect is the angular distance between two planets along that circle, measured from Earth. Traditional astrology recognizes five major aspects, all based on dividing the circle by whole numbers: in half (opposition), in thirds (trine), in quarters (square), in sixths (sextile), and not at all (conjunction).
The planets involved tell you what is being connected. The aspect tells you how they get along. A good habit is to read every aspect as a sentence: "my need for comfort (Moon) and my sense of duty (Saturn) are in tension (square)." That turns a technical label into something you can recognize in yourself.
The element and modality patterns behind these are explained in elements and modalities.
Planets rarely sit at exactly 90 or 120 degrees apart, so astrologers allow a margin called an orb. If the Moon is at 10° Aries and Saturn is at 14° Cancer, they are 94 degrees apart: a square with a 4-degree orb.
There is no single agreed orb table, and practices vary. A common modern approach is:
The tighter the orb, the stronger and more noticeable the aspect. A Sun-Moon square with a 1-degree orb is a central theme of a chart; one with a 7-degree orb is a background note. Astrologers also note whether an aspect is applying (the faster planet is moving toward exactness) or separating (it has already passed), with applying aspects usually read as a bit stronger.
Sometimes planets are within orb but in signs that do not normally make that aspect, such as 29° Aries and 1° Leo. They are 92 degrees apart, a square by distance, even though Aries and Leo are both fire signs that would normally form a trine. These are called out-of-sign aspects. Many astrologers still count them, though they read as a little less straightforward.
Take Venus trine Mars. Venus is how you attract and what you enjoy; Mars is how you pursue and assert. A trine lets them cooperate. This often reads as someone whose affection and desire line up, who finds it natural to go after what they want in love, and who tends to be comfortable with both giving and receiving attention. The shadow side of such an easy aspect might be expecting romance to always flow without effort.
Now take Venus square Mars. The same two needs are in tension: what you find attractive and how you pursue it pull in different directions. This can show up as attraction to people who challenge you, as sparks that are exciting and sometimes combative, or as a restless streak in relationships. The tension also generates energy, creative and romantic, that a trine does not.
Notice that neither reading is simply good or bad. Hard aspects bring friction and motivation; soft aspects bring ease and, sometimes, complacency. Most people have a mix, and the mix is what gives a chart its texture.
Beyond the big five, some astrologers use minor aspects with tight orbs of one or two degrees. The most common is the quincunx or inconjunct (150°), which links signs that have nothing in common and is often read as a need for constant adjustment. The semi-sextile (30°), semi-square (45°) and sesquiquadrate (135°) also appear in detailed readings.
When several aspects link up, they form patterns. A T-square is two planets in opposition with a third squaring both, a strong, driven configuration. A grand trine is three planets in trine forming a triangle, usually all in one element, a sign of a natural talent that flows easily. A stellium is three or more planets clustered in one sign or house, which concentrates a lot of attention in one area.
Aspects are not only read inside one birth chart. In synastry, the aspects between one person's planets and another's describe how two people affect each other: her Moon trine his Sun, his Mars square her Venus, and so on. This is what makes full-chart compatibility more detailed than comparing Sun signs, as on a page like Taurus and Scorpio.
In transits, the moving planets of today make aspects to the planets in your birth chart, which is how astrologers talk about timing.
Vedic astrology treats aspects differently. Its planetary aspects (drishti) are counted by whole signs: every planet aspects the sign opposite it, Mars also aspects the 4th and 8th signs from itself, Jupiter the 5th and 9th, and Saturn the 3rd and 10th.
Start with aspects involving the Sun, Moon and the planet that rules your rising sign, and look for the tightest orbs first. Those will usually describe the themes you recognize most. You can see your own birth chart on My Stella to see where your planets sit and how far apart they are.
No. They describe tension, and tension produces effort, drive and growth. Many accomplished, capable people have charts full of squares. Easy aspects bring comfort, and sometimes less motivation to develop a gift.
There is no fixed standard. A common range is about 8 degrees for conjunctions and oppositions, 6 to 8 for squares and trines, and 4 to 6 for sextiles. The tighter the orb, the stronger the aspect.
It depends on the planets. A conjunction fuses two energies, so Venus with Jupiter tends to feel easy while Mars with Saturn tends to feel pressured.
Mostly not. Planets move slowly enough that aspects between them are usually the same across a whole day. Aspects involving the Moon, which moves about 13 degrees a day, or the Ascendant and Midheaven do depend on birth time.