If you equate solar months and the zodiac, the 1400 BC Vedangajyotisha talks about twelve solar months.
लगधेन ग्रथिथां, वेदाङ्ग ज्योतिषं, श्लोकं 28: (see pages 42, 43 of the linked PDF)
त्रिशत्यलिनां सषाश्तिर् अब्दः षट् चार्तवोfयने
मासा द्वादश सूर्यः स्युः एतत् पञ्चगुणं युगं
Three hundred and sixty-six days form the solar year. In the year, ...
Astrology is used to predict future events and find solutions or prevents from any negative event to be occurred.
Considering your question , if a doctor operates a patient who is suffering from a disease and prevents it from teatment and saves a patient life does he get a bad karma ? It's just his mere duty (karma) to save patient and so it's an astrologer ...