Reiwa (令 和) is officially announced today and goes into effect from May 1, 2019, beginning the era attributed to the eldest son (Firstborn) of Emperor Akihito
The Heisei era (平 成) began on January 8, 1989, just a day after the emperor’s death, Hirohito.
Traditionally, the first-born children are considered first in the line of succession of titles of nobility after the death or abdication as was the case of the Akihito Imperdor.
Here are some eras:
Meiji (明治 1868-1912)
Taisho (大 正 1912-1926)
Showa (昭和 1926-1989)
Heisei (平 成 1989-2019)
Reiwa (令 和 2019 to …)
Source: ANN News, TBS News & Wikipedia