Julius Caesar's astronomers explained the need for 12 months in a year and the addition of a leap year to synchronize with the seasons. At the time, there were only ten months in the calendar, while there are just over 12 lunar cycles in a year. Show
The months of January and February were added to the calendar and the original fifth and sixth months were renamed July and August in honour of Julius Caesar and his successor Augustus. These months were both given 31 days to reflect their importance, having been named after Roman leaders. Which years are leap years and can you have leap seconds? Why seven days in a week?While months, years and days can be directly related to astronomical events like the rotation of the Earth around its axis or a complete orbit of the Sun, a week is a curious 23% of a lunar month. Nevertheless, it has been used for millennia from China to India, the Middle East and Europe. Our use of the sevenday week can be traced back to the astronomically gifted Babylonians and the decree of King Sargon I of Akkad around 2300 BCE. They venerated the number seven, and before telescopes the key celestial bodies numbered seven (the Sun, the Moon and the five planets visible to the naked eye). The sevenday week is also closely linked to Judaism and the story of Genesis, with God resting on the seventh day. Al Hijra, Ramadan and the Islamic calendar Why is the day divided into 24 hours?The Ancient Egyptians were the first to use 24 hours to divide the day. They divided the day into 12 hours from sunrise to sunset, and the night into a further 12 hours from sunset to sunrise. Why are minutes and hours divided into 60?When the hour was divided into 60 minutes, consisting of 60 seconds, the number 60 may have been chosen for its mathematical convenience. It is divisible by a large number of smaller numbers without a remainder: 2, 3, 4, 5, 6, 10, 12, 15, 20 and 30. Discover gifts from the home of timeKeep track of time with Royal Observatory Greenwich watches, and our famous Shepherd Gate clock, reproduced for your wall at home Shop Greenwich Shepherd Gate 45cm Wall Clock, 24Hour Analogue Dial £150.00 Own a Shepherd Gate 45cm clock, exclusively available from the home of Greenwich Mean Time. A stylish 24hour analogue clock that will make a statement on any wall, with its bold monochrome face, and matte black metal casing... Buy Now Shop On the Line: The Story of the Greenwich Meridian £8.99 The Royal Observatory at Greenwich is the home of time and space, the Prime Meridian and Greenwich Mean Time (GMT). But have you ever stopped to ask what is the Prime Meridian and why it is at Greenwich? Why are all time zones across the world based on GMT? What is longitude and why is the meridian moving? Written by Dr Louise Devoy, Senior Curator of the Royal Observatory at Royal Museums Greenwich... Buy Now Shop Royal Observatory Greenwich John Harrison's H4Inspired Chrome Pocket Watch £175.00 A stunningly crafted, chromeplated half double hunter pocket watch inspired by John Harrison’s worldchanging chronometer... We hope this time calculator will save you some headaches by making the basic operations on time easier. It is quite universal to have problems with time  from time to time, we: Race against time, live on borrowed time, work overtime, give someone a rough time, hardly have time to breathe, dance out of time, kill time, and waste the hours in an offhand way. How to manage all these time problems? The time and date calculator lets you subtract time (find time difference), multiply time, divide time, add time, and calculate the time between dates. It also incorporates a timetotime calculator (you can check time duration, e.g. how many days and hours passed from 2.03.2010 11:00 am to 3.04.2010 6:30 pm). In the text, you'll find instructions on how to use each part of the calculator and how to calculate time manually. If you still haven't found the time calculator you're looking for, check out our:
Add time calculatorTo use the add time calculator:
Example: You've written down your tasks for the evening and want to know how long they will take you in total:
To find out how long it'll be before you put your feet up, input the time values in the time calculator. You don't need to change the unit  if you want to enter only minutes, click the blank place next to "min" and type in the number. The hours and minutes will automatically become zeros. You can find your result at the bottom of the time calculator  the tasks should take you 2 h 20 min in total. Subtract time calculatorTo use the time difference calculator:
You can also use the time calculator as a time duration calculator. If you want to find the duration between times:
Multiply time calculatorTo use the multiply time calculator:
Example: You have to paint a fence. You've already done 1/5 of the work, and it took you 23 minutes. You want to estimate how long it takes to paint the whole fence.
Time calculator  divisionTo use the divide time calculator:
Example: You're soon starting a twoweek holiday, and you decided to spend 1/3 of this time (including sleeping hours) on the beach with your other half. To count it:
Date time calculator  calculate the time between datesTo use the date time calculator:
Example: You have an exam on 18.10.2020 and want to know how many days you've got left to prepare. Today is 22.09.2020.
Time and date calculator (time to time calculator)This option is similar to the time between dates calculator, but it's more precise and takes time (hours) into account. Let's say you want to use the time and date calculator to know your exact age. In this case:
This time to time calculator has an accuracy of half an hour (you can only choose 11:30, you cannot choose 11:27). If you need more precision, use the elapsed time calculator. You could also use this time calculator  just enter a later hour in 24hour format in the first field and an earlier hour in the second field. How to add time manually?Calculating time may be complicated because of the hexadecimal system. What does it mean? Simply put, it means 60 "smaller units" make up 1 "bigger unit", e.g., 60 seconds equals 1 minute and 60 minutes equals 1 hour. We're more used to the decimal system where 1 "bigger unit" is comprised of 10 (or 100, 1000, etc.) "smaller units", e.g. 10 grams are 1 dekagram. Keeping that in mind, let's go through some examples: Time addition Example:
How to subtract time without the time calculator?Example: First method:
Second method: This is similar to the way you would do long division.
How to calculate time?  multiplicationExample:
How to calculate time?  divisionExample:
If you need some instruction on how to calculate the time between dates without the time calculator, check the example in the date calculator. FAQHow many seconds are in a day? How many seconds are in a year?In a day, there are
To find the number of seconds in a year, multiply the result by Why are there 60 seconds in a minute and 60 minutes in an hour?The number 60 in the way humanity counts time is a heritage of the way the early civilization from Mesopotamia counted numbers. Sumerians and Babylonians, in particular, counted using base 60, which is relatively complex compared to the current, widespread base 10. However, those first attempts at math still exist in our angles, clocks, and maps. How do I calculate the day passed between two dates?To calculate the time between two dates,
Multiply years by How do you calculate the number of hours you spend commuting in a month?Let's assume that you commute from and to work 20 days a month, and each trip takes 35 minutes. You can compute the hours spent commuting using the following steps:
Almost a day. You need to find some activities, like reading, to ensure that you gain some benefits from that time! How many minutes are there in a month of 30 days?A month has 44,640 minutes in total.
Is half an hour 60 minutes?There are 60 seconds in 1 minute. There are 30 minutes in a half hour. This means there are (30 x 60) 1800 seconds in a half hour.
What is the half of 1 hour?a period of 30 minutes.
Is half an hour 20 minutes?It is common to talk about 'half an hour' (30 minutes) and 'quarter of an hour' (15 minutes).
