According to the article,it's actually the 23rd anniversary. Obviously a typo, since in 1961, Ukraine, as part of the Soviet Union at the height of Nikita Khrushchev's power, was hardly independent.
August 24,1991 The Act of Declaration of Independence of Ukraine was adopted by the Ukrainian parliament on 24 August 1991.
Act of Declaration of Independence of Ukraine
In view of the mortal danger surrounding Ukraine in connection with the state coup in the USSR on August 19, 1991,
Continuing the thousand-year tradition of state development in Ukraine,
Proceeding from the right of a nation to self-determination in accordance with the Charter of the United Nations and other international legal documents, and
Implementing the Declaration of State Sovereignty of Ukraine,
the Verkhovna Rada of the Ukrainian Soviet Socialist Republic solemnly declares the Independence of Ukraine and the creation of an independent Ukrainian state – UKRAINE.
The territory of Ukraine is indivisible and inviolable.
From this day forward, only the Constitution and laws of Ukraine are valid on the territory of Ukraine.
This act becomes effective at the moment of its approval.
— VERKHOVNA RADA OF UKRAINE, August 24, 1991