Ketu is a fiery planet. It signifies the quality of ignorance, hence it is called the tamsic planet. Ketu signifies the maternal grand father, occult, a surgeon, a mathematician, a pilot, sense of smell, law, lawyers and politicians.
planet man
When Ketu works through lower principle, it signifies the mafia world, mystic activities, unfortunate person or event, wounds, suffering, misery, poisons, scandals, skin diseases, scavengers, parasites, strong noxious smells, homeless, destitute, bad company, infections, false pride, selfishness, secret intrigues and associations, habit of backbiting, bankruptcy, madness, spying  activity, etc.

When Ketu works through higher principle, it signifies moksha(final emancipation from the life-death cycle), spiritual initiation, practice of yoga, sudden gain, renunciation, deep space exploration, place of religious and occult significance, artistic taste, literary genius, philosophical outlook, etc

Ketu appreciates items like weeds and fruits and prefers adoration on Sundays and Tuesdays.  Ketu does not live in the same abode as Rahu.  If you want to make him happy, you must adorn yourself with the jewel, cat’s eye. 

Conjunction of Ketu with any planet in the birthchart makes the planet weak. Specially if Ketu is in conjunction with Jupiter, Saturn or with Mars or with Moon also makes a very bad effect in life. Conjunction of Ketu with any Auspicious planet requires a remedy. Point to be noted here is opposition with any Auspicious planet means conjunction of the same with Rahu as Rahu is always in opposition with Ketu. Hence Opposition of Ketu also makes the planet weak. And requires a remedy as per Indian astrology.

Ketu behaves like Mars, hence all ailments represented by Mars can be also caused by Ketu. In addition to those it can cause chicken and small pox, viral fevers, intestinal worms and problems of feet and anus.

Ketu mainly influences the blood and skin. If Ketu in a chart is strong and benefic, then the native is bold, energetic, enthusiastic and active. Also it gives recuperative powers and resistance to diseases.

Ketu is the headless half planet. It governs the number seven in Indian Numerology. In the Hindu Astrology, Ketu stands for bad and good, supernatural and spiritual influences. Ketu related with the Meena Avatar, i.e. Fish incarnation of the lord Vishnu. Ketu indicates the religious process of the modification of personification to spirit. It is regarded as both benefice and malefic. It causes loss and grief. At the same time it leads the individual to become a spiritual person. So we mat say that material loss is happened in order to turn into a holy person. Ketu is a pointer of intelligence, prudence, dream, acute insight and supernatural abilities. Ketu brings wealth to devotee’s family. It eradicates the possibility of biting the snake and death due to the poison. It provides prosperity, god health and cattle to his followers. It is the owner of 3 stars i.e. Ashini, Magha and Mula. Those people who come under the control of Ketu may obtain spiritual life.