### Theory:

Ordinary year:
$$1$$ year $$=$$ $$12$$ months

$$1$$ year $$=$$ $$52$$ weeks $$+$$ $$1$$ day

$$1$$ year $$=$$ $$365$$ days

$$1$$ month $$=$$ $$30$$ days or $$31$$ days

$$1$$ month $$=$$ $$4$$ weeks $$+$$ few days

$$1$$ week $$=$$ $$7$$ days

Ordinary February month has $$28$$ days.
Leap year:
$$1$$ year $$=$$ $$366$$ days

$$1$$ day is added in the month of February.

Important!
In a Leap year, February month has $$29$$ days.

Leap year comes once in every four years.
Identifying a leap year:
A year which is divisible by $$4$$ is a leap year.

A century which is divisible by $$400$$ is a leap year.
Periods of time:
$$10$$ years $$=$$ $$1$$ decade

$$100$$ years $$=$$ $$1$$ century

$$1000$$ years $$=$$ $$1$$ millennium
Jubilee:
A jubilee is a particular anniversary of an event.

$$25^{\text{th}}$$ $$-$$ Silver Jubilee

$$40^{\text{th}}$$ $$-$$ Ruby Jubilee

$$50^{\text{th}}$$ $$-$$ Golden Jubilee

$$60^{\text{th}}$$ $$-$$ Diamond Jubilee

$$65^{\text{th}}$$ $$-$$ Sapphire Jubilee

$$70^{\text{th}}$$ $$-$$ Platinum Jubilee

Important!
The study of measurement of time is called as "HOROLOGY".