The year is a unit of time that is a multiple of an SI unit and uses the symbol a.
The Julian year is made up of exactly 365.25 days – each with 60 x 60 x 24 seconds (86,400 seconds). The .25 days is worked into the system by counting 366 days once every 4 cycles. This is known as a “leap year” and the “leap day” happens at the end of February.
The term year represents the length of time it takes for the earth to complete one full cycle around the sun. Each planet therefore has a different year length.
To track years, humanity has assigned an incremental numbering system. Depending on which culture, religion or part of the world you are from or follow, this number varies. The most common numbering system suggests we are in the 21st century – i.e. in the 2000’s. This system started 0 AD (Anno Domini – which translates from Latin as “In the year of our Lord”). Time before this is referred to as BC (before Christ) and the number increases as you go further into history (like a negative number would).
The month is a unit of time and is a multiple of an SI base unit with the symbol mo.
There are 100s of definitions of a month that have been established, reviewed and adopted over the course of history but the most common around the world today are the months in the Julian and Gregorian calendars.
There are 12 months in the Julian and Gregorian year; averaging 30.4368 days in each. They are labelled January, February, March, April, May, June, July, August, September, October, November and December.
There is a famous rhyme to help remember how many days are in each month that goes “Thirty days has September, April, June and November – all the rest have thirty-one. Except February which has 28 or 29 in a leap year.”
Many cultures use the moon’s cycle (the lunar cycle) to define which month they are in.