A week number is a sequential number that a week has in a year.
A year is a relative unit of time. It describes a specific period during which the planet revolves around the sun. But we rarely ever speak about this when we try to explain the concept of a year to others. A year is a period which is counted in days. According to the gregorian calendar a year has 365 days. Every four years an extra day is added. This extra day is being added because the revolution around the sun can not be measured in exact days. This year we call a leap year. Besides the Gregorian calendar there is also the Julian calendar. This calendar had once every four years a leap day. On average this year lasted 362,25 days. The Gregorian calendar has less leap days. According to this calendar the years last 365,2421875 days.
A period between two Vernal Equinox passages of the sun is called a tropical year. This is about the two moments that the sun is pointing in the same direction moving above the equator.
There are different definitions of the word year. The tropical year has been discussed above, but there is also a sidereal year. This is the period after which the stars are again on the same place in the sky. Then there is also the anomalistic year. This is about a period between passages of the earth through the perihelium in the earths’ orbit. Lastly there is also the draconian year. This is about the period that the sun requires to complete a full cycle in relationship to the same moon node.
A year can start and end at different moments. 22nd of June until the 21st of June. But if you are talking about a calendar year, then it is about the period between the 1st of January until the 31st of December. What other kind of years do we know?
A year has 52 weeks in total. This means that a year has 52 full weeks, then there is one day left if you are counting in the normal years. If we are discussing a leap year then there are 2 extra days remaining. A normal year has 365 days and a leap year has 366 days.
Once every four years there is a leap year. This means that there is a day more in this year. If this was not installed then the seasons would not match the calendar. For example, Spring would start earlier on in the year. We notice the extra day in February. Normally we would transition from the 28th of February to the 1st of March, but in the case of a leap year there is also an extra day, namely the 29th of February. A lot of people have been born on the 29th of February and they celebrate their birthday on the 1st of March for instance.
A year usually lasts 365 days, but in fact it is different. The earth takes a year to circle around the sun. It does not take 365 days, but to be precise it takes 365 days, 5 hours, 48 minutes and 46 seconds. If you round the decimals this would mean that after four years you are one day short in time. If this would happen for 40 years then we would miss ten days. If this would happen for a century then we would miss almost a month and this would mean that Christmas would be in Autumn for instance. Would we then ever have a white Christmas? These are fun facts to understand how the concept of time can also be looked at.
