Astrologically planets are ascribed exaltation and debilitation points in the zodiac. As a rule the Rasi (sign) in which the exaltation and debilitation point is located is taken as a whole as exalted or debilitated sign. The point of debilitation from the point of exaltation is 180 degrees. The 7th sign from the sign of exaltation is the debilitation sign.
Sun Aries 100 Libra 100
Moon Taurus 30 Scorpio 30
Mars Capricorn 280 Cancer 280
Mercury Virgo 150 Pisces 150
Jupiter Cancer 50 Capricorn 50
Venus Pisces 270 Virgo 270
Saturn Libra 200 Aries 200
The why, how and what of exaltation and debilitation of planets are not explained in any authoritative work of astrology.
The argument put forth by some is that the planet nearer to earth is potentially strong and hence is exalted. A study of the following dismisses that argument.
The distance and exaltation or debilitation of planets is not in any way connected. Then what is debilitation and exaltation of planets ?
Exaltation means being in high position, exhileration and strength. Debility means weakness, and humility.
The zodiac is the planetary cabinet. The first house or sign should be occupied by protocol by the King as the Ist citizen. Sun is the king of planetary cabinet. Hence he should be exalted on his thrown in the Ist sign Aries. A king enjoys power and position only when attended by the commander in chief Mars and the servant Saturn. Aries is the sign owned by Mars, the commander in chief of the planetary cabinet and Saturn the servant is debilitated (humbled) in Aries due to the authority of the King and the commander in chief. The King is attended on either side (Pisces and Taurus by Venus the courtesan and the Queen Moon).
The place next to the King shall go only to the Queen. Hence Moon is exalted in Taurus. Sun owns Leo and Moon owns Cancer and get exalted in Aries and Taurus respectively. Next to Queen no one can sit. Hence Gemini has neither exaltation or debilitation of any planet in it. Cancer is owned by the Queen (Queen's place) Moon. Jupiter is the preceptor and further has a respectable place in the Queen's palace when he visits Cancer. Hence Jupiter is exalted in Cancer. Mythologically Moon (as male disciple of Jupiter) has an episode with Tara, the wife of Jupiter, which culminated in the birth of a child Budha. Mars the commander in chief visits the Queen's palace to carry out the commands or run errands of the Queen. Hence he is debilitated in Cancer. In the King's palace of Leo no planet can be exalted. Hence free from exaltation or debilitation. Virgo is owned by Mercury. Mercury is the finance minister in the planetary cabinet hence exalted in Virgo. Venus the courtesan is debilitated in the house of the finance minister, personally visiting for financial aid. Libra is owned by courtesan (damsel). When the king visits the court damsel, naturally he is accompanied by the servant Saturn. In the house of a damsel the king looses his authority. Hence is debilitated in Libra. The servant Saturn is the master of the situation (arranging meeting of Damsel Venus and King Sun) and is exalted. Scorpio is owned by Mars. When Moon the Queen visits the quarters of subordinate commander in chief, she is humbled. Hence is debilitated in Scorpio. In the mansion of the Guru Jupiter no planet is exalted or debilitated. Capricorn is the quarters of the servant and soldier Saturn. Mars visits the barracks of soldier. He the commander in chief visits with authority. Hence is exalted. Jupiter the preceptor and prime minister by visiting the quarters of a servant looses his dignity and status.
Hence Jupiter is debilitated in the house of Saturn - Capricorn Aquarius also is owned by Saturn. There is no debility or exaltation of planets in it. Pisces is owned by Jupiter. Venus, the damsel, being in the house of respected Jupiter in the proximity of the king In Pisces naturally has power hence is exalted. Finance Minister, and in the proximity of the king is subdued of his authority and hence is debilitated in Pisces.
This is one line of explanation of exaltation and debilitation of planets on the basis of planet politics.