BHISHMA WAITED FOR UTTARAYANA IN ORDER TO DIE

Yudhishthira declines Lord Krishna to participate in the war, Bhishma  assists Pandavas and accepts his death by laying down on bed of arrows 

We all comprehend that Bhishma was blessed with the boon of 'self-willed death' by his father Shantanu; the king of Hastinapura on the fact of Bhishma taking the vow of staying a celibate till the cease if his life and sacrificing the throne of Hastinapur. Bhishma used to be so courageous that even deities could not defeat him. During the Mahabharata war daily Bhishma slew ten thousand soldiers and destroyed many chariots. Pandavas had no clue how to kill him. Lord Krishna additionally raised his Sudarshana chakra against Bhishma in order to kill him but was stopped by Arjuna during the Mahabharata war. 

The night before the tenth day of the Mahabharata war, Pandavas along with Krishna had a discussion over the huge destruction of their army by way of Bhishma. Pandavas had no clue how to defeat such an invincible warrior like him. Lord Krishna had consoled Yudhishthira and asked for his permission  to let Krishna himself take part in the great Mahabharata war and kill Bhishma.  He knew that Despite  taking an oath to kill Bhishma Pitamaha, Arjuna Could not  fulfill it out of maintaining affection towards him. Yudhishthira with courtesy denied Krishna to fight in the war on the grounds that Krishna had already cited before no longer to raise weapons in the Mahabharata war and  Yudhishthira didn't want Krishna's statement to be turned out as a lie. On the other hand, Yudhishthira at that time recalled the condition of Bhishma that was set by him  prior to the war that 'Bhishma would give  advice  to Pandavas for their benifit  during the war but he would only fight in the favor of Duryodhana'. Therefore Yudhishthira alongside his brothers and Lord Krishna went to Bhishma  Pitamaha in order to seek for his advice regarding his own death.

Bhishma referred to them that, "I never prefer  fighting with a warrior who has already  lowered  down his weapons or has no armor and dhwaja, has  been   running away from war, has  already  surrendered to me, would be the only son of a father, any high caste individual, and any females or person having lady name. I can never raise any weapons at Sikhandi: born to the queen of Panchala king Drupada, as a woman however later grew to be a man. I know Sikhandi was Amba in his previous birth. Hence I suggest Arjuna to bring me down via shooting arrows while keeping Sikhandi as his shield." Bhishma knew that only Arjuna or Lord Krishna could kill him. Bhishma already knew that It was destined by Lord Brahma that only Arjuna would kill him.

Likewise next day during the war, Bhishma killed many armies of Yudhishthira furiously. Arjuna observed Bhishma's instructions. Sikhandi attacked Bhishma which was ignored by Bhishma.  Arjuna then  pierced Bhishma's whole body by shooting many arrows at him. Bhishma knew he could fight back with Arjuna as he was doing it during the war earlier  however, he choosed to accept his death instead, for this reason, gave up a counter-attack.

All the vasus after understanding the decision of Bhishma appeared in the sky and gladly supported him. Out of pain Bhishma  even raised shakti weapon towards Arjuna however he destroyed it it. Shockingly that time Bhishma in spite of being surrounded by the armies alongside the remarkable warrior kings of Kaurava side, could not get rescued. Though Bhishma had already made up his mind for his death, Arjuna defeated all of those warriors and made Bhishma fall down from his chariot by shooting innumerable arrows at his body. Bhishma's body used to be already pierced thru the arrows consequently after falling down, his body stayed untouched on the earth. Bhishma could have died that very moment. But He discovered it was not the auspicious time because of 'Dakshinayana of sun'.

(In a year sun changes his position twice for a period of six months. Uttarayana or summer solstice is regarded as auspicious, starting from Makara sankranti and all yajnas, donations, marriages are carried out during such holy period. While Dakshinayana or winter solstice is acknowledged to be suitable for Tamasik things to do which are fulfilled with lust, desires, And negativities. Bhishma did not desire to sacrifice his life during Dakshinayana and decided to wait until the holy period of Uttarayana of sun started.)

While laying down on the bed of arrows or on 'sarasajya' Bhishma had asked Arjuna to provide him a suitable pillow for his head since his head needed support. Many Kauravas had presented him with gentle and satisfactory pillows however Bhishma rejected them. After taking permission of Bhishma, Arjuna had shot three arrows closer to the earth to let Bhishma rest  his head on those arrows. Later Bhishma out of suffering  caused by the shot arrows, wished to have water and asked Arjuna to provide him. Since Bhishma was going to die, he did not desire to have something associated with the human world. Then Arjuna moved in a circle on his chariot around great Bhishma,  shot a divine arrow on the earth to the right hand side of Bhishma. Shockingly Water came out of the place and quenched Bhishma's thirst.

Ref: Mahabharata book

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