How it feels from the inside
From the inside, a Sun in Aries often feels like an engine that is already running. Ideas arrive as things to do. You may notice that the first weeks of a new project, a new job or a new city are when you feel most like yourself, and that the long middle, with its upkeep and waiting, tires you faster than hard work ever does.
Purpose tends to take the shape of a challenge. A goal that someone calls impossible can pull harder than one that is merely sensible. You may measure yourself against other people without meaning to, and against your own last attempt even more. Decisions come quickly and from the gut, and the reasons often arrive afterwards. When something goes wrong, the instinct is to act at once, and sitting with an open problem can feel close to unbearable.
How it shows in love and at work
Others usually meet the Sun in Aries as frank, energetic and easy to read. You say what you think, and people rarely have to guess where they stand with you. In a group you are often the one who proposes the plan, or who asks the question everyone else was stepping around.
In love this Sun tends to pursue rather than wait. It shows interest openly and is drawn to people who are a little hard to win. From a partner it wants honesty and a spark of challenge: someone with their own momentum, who will not be flattened by its directness and will push back when it goes too far. It needs independence inside a relationship, and being managed or smothered brings out its restlessness. Arguments can flare fast and be over just as fast. An Aries Sun rarely keeps a grudge; it is usually too busy with the next thing.
At work this Sun is at its best where something has to begin or be decided: opening a new line of work, handling a crisis, taking on the task nobody has tried. It works well with a clear target and freedom over how to reach it, and it chafes under slow approvals and long chains of permission. Given the right problem, it brings an energy that spreads to the people around it, and the nerve to go first.
Where it tends to struggle, and the strength inside that
The difficulties come from the same fire. Impatience can make an Aries Sun start more than it finishes, or leave the careful part of a job to others. The Sun's focus on the self, pushed on by Mars, can turn into thinking of your own aim first and other people's second. Anger arrives quickly, and words said in the heat of it can land harder than you meant. Losing, or being made to wait, can sting out of all proportion.
The strength inside all this is courage. The Sun in Aries can act while others are still hesitating, and it recovers from a setback quickly because it is already looking at the next attempt. Its honesty tends to be free of calculation: what you see is what it means. It is often the person who knocks on the door first, and the one who knocks again after being told no.
Beside other Suns, and beside your Moon
The opposite sign, the Sun in Libra, is where tradition places the Sun's fall. There identity comes into focus through other people, through weighing and balancing, while Aries finds itself alone and in action. Among the fire signs, the Sun in Leo is the Sun's own sign. It wants to shine steadily and be seen, where Aries would rather be first than be watched. The Sun in Sagittarius shares the fire but aims it at meaning and distance, following a question rather than a contest.
The Sun and Moon in Aries are easy to confuse. A Moon in Aries describes quick emotional reactions and a need to act on a feeling, while a Sun in Aries describes a direction and an identity. With a calmer Moon or rising sign, the Aries Sun may show less at a first meeting than in the choices a person makes over the years. The big three calculator shows all three together.