Vyatipata is the 17th Nitya (Naisargika) Yoga, which is ruled by Rudra and considered to be especially malefic one along with Vaidhriti (comparing to other malefic Nitya Yogas all Ghatis of Vyatipata and Vaidhriti are inauspicious for starting something). Both Yogas should be shunned in all auspicious elections. According to classical Jyotirvidyabharanam (2/56) any religious activity done during these Yogas do not yield any result in both "lokas", i.e. it's completely destroyed. Another classics, Rajmartanda opines that these Yogas along with Bhadra Karana (Vishti) are even capable to destroy even Amrita Yoga. Its effect can be described as "a portent indicating disaster", "a great disaster", "calamity". Rahu is a Graha, who's ruling Vyatipata.