i want to know ,what is the significance of 9th Rabi-ul-awwal ?
Eid is any day that there is happiness in that day. The significances of 9th Rabi-ul-awwal is that this day is the day that killers of Imam Hussain a.s. at Karbala were destroyed:
One particular hadith which speaks of this day tells us that while in
a gathering with the Prophet of Islam, Imam Ali and his two sons,
Hasan, and Husain (blessings be upon all of them), the Prophet, with a
smile on his face, said, “It is on this day that Allah will destroy
your enemies and the enemies of your grandfather and it is on this day
when Allah will accept the actions of your Shia and those who love
you. This is the day when the words of Allah came true where He said
(in the Qur`an): ‘So those are the houses fallen down because they
were unjust…’ (27:52) And this is the day when the Pharaoh (Firawn)
of the time of the AhlulBayt was destroyed…”
It is after going through close to 80 days of grief and sorrow in which we commemorated the murder of Abi Abdillah al-Husain (peace be upon him) and his family and friends in Karbala and the other Shahadats which we have marked over this period - including the loss of our 2nd Imam, 4th Imam 8th Imam, 11th Imam, and of course our beloved Prophet Muhammad (may the prayers of Allah be upon him and his family)
Also this day is the start of the Imamate and leadership of 12th and Living Imam, Imam Mahdi (may Allah hasten his return).
Reference:
Celebrating Eid e Zehra (sa) & Beginning of Leadership of Imam Mehdi (ajtfs)