The launch rate is approximately one per year, with selection of two missions occurring every two years.
For this group, it has been a regular event, occurring every five years since the chorus's 25th anniversary, in 1977.
With the election occurring every six years, it would be like World Cup, American Idol, and Papal appointment all wrapped into one.
In the 1960s, droughts were strongly episodic, with one drought occurring every four years (1961, 1965, 1969).
The upper house, known as the Rajya Sabha, is a body whose members are indirectly elected to six-year terms with staggered elections occurring every two years.
Additionally there is CONMEBOL, a soccer confederation headquartered in Paraguay, comprising of 10 members associations representing organized soccer in South America, with Copa América occurring every two years as their main tournament to determine the regional champion of South America.
The Olympic Games are held every four years, with the Summer and Winter Games alternating by occurring every four years but two years apart.
And then there is the most watched sporting event occurring every four years on the face of the earth and it's not the Olympics, but the FIFA World Cup soccer.
In the last several decades, the lakes have risen and fallen dynamically, with record high levels in the late 1980s, and "100 year storms" and flooding occurring every five years.
