If the Sun is in the 3rd house, the person will be courageous, brave, and adventurous. He will be bold and powerful and desire a position of authority. He will be motivated, and his efforts will succeed with perseverance. There will be little happiness with brothers and sisters. The person is firm or stable in his desires. The next-born sibling is male.

UCHCHA and SWAKSHETRA (exalted and own sign). If the Sun is in Aries or Leo in the 3rd house, the benefits mentioned above are heightened. The person has a special or famous younger brother or sister. He will be powerful and courageous. He will be highly motivated, and his efforts will succeed easily. The person may attain distinction in the literary field or any profession involving communications. He will be a very strong personality. His desires will be fulfilled.

NEECHA (fallen). If The Sun is in Libra in the 3rd house, the person's desires are intense, constant, and nearly insatiable. His efforts are unsuccessful, and his desires may remain unfulfilled. He will have problems with his brothers and sisters, or have none at all. The next younger sibling will lead a difficult life or die early. The person may lack excitement or be unmotivated. He will be cowardly and fearful. He will have no talent in the fine arts.

Source: «Ancient Hindu Astrology for the Modern Western Astrologer» by James Braha