Note that we never write ‘16:10pm’ The use of am and pm is only for the 12-hour clock. For example, 4:10pm is the same time as 16:10. Time before midday (noon) is designated am ( ante meridiem) and time after noon is referred to as pm ( post meridiem). When using the 12-hour clock the 24 hour period is divided into two 12-hour periods. This is especially common in military and seafaring situations. For example 1400, which may be referred to as fourteen hundred hours. You will often see the time in 24-hour clock written without a separator (‘.’ or ‘:’) between the hours and minutes. When using the 24-hour clock, the 24 hour cycle starts with the time 00:00 (midnight) and runs all the way through to 23:59, before rolling over to 00:00 again. Hours may be either divided into 24 (known as the 24-hour clock) or two lots of 12 (often referred to as the 12-hour clock). The simplest (digital) form is as written hh.mm or hh:mm, for example 10.21 or 10:21. There are many different ways to write time. This makes it hard to convert from months to weeks and vice versa, unless you know which months are being used, because there is no immediate ‘conversion factor’. For example, it is common to use the assumption that a month contains four weeks, even though only February in a common year actually does so. People often use approximations when calculating the number of days in months. Quarter 1Īs the number of days in a month varies, this also means that the number of weeks in a month varies too. All months have the same number of days each year except for February which has 28 days in a common year and 29 in a leap year. Quarters in a specific business or sector may not necessarily be the same as those indicated below: Years are commonly split into quarters, especially in business and education settings, with each quarter being three months or approximately 90 days. A common year has 365 days and a leap year (occurring mostly every 4 years) has 366 days. February has 28 days in a common year and an extra day in a leap year the 29 th day of February is called the leap day.Ī year always has 12 months. All months have either 30 or 31 days except for February. It is also common for people to talk about a work week, usually 5 days (Monday - Friday) and weekends (Saturday and Sunday).ĭifferent months have different numbers of days. It is common to talk about 'half an hour' (30 minutes) and 'quarter of an hour' (15 minutes). These 'leap seconds' are used to keep our clocks aligned to the earth's rotation around the sun. once every 18 months) a minute can have 61 seconds. Seconds are also commonly abbreviated to sec.Ī minute nearly always has sixty seconds. The symbol 's' is used to denote a second. The second is the International System of Units (SI) measurement for time. The basic units of time, which allow you to do calculations involving time, are: Unit However, with a bit of application, you too can learn how to calculate with time, and gain confidence in manipulating hours, minutes and seconds. For example, Earth’s average temperature has been increasing much more quickly than they would expect over the past 150 years.Even otherwise highly numerate people have been known to throw up their hands in horror at the thought of adding together times.Ī system like time, which is not decimal, can be counter-intuitive and requires concentration. However, scientists have observed unusual changes recently. Changes in flower and plant blooming times.Įarth’s climate has constantly been changing - even long before humans came into the picture.Ice melting at a faster rate than usual in Greenland, Antarctica and the Arctic.These include warming temperatures and changes in precipitation, as well as the effects of Earth’s warming, such as: Global climate change refers to the average long-term changes over the entire Earth. In the United States today, we have a warmer climate and fewer glaciers. For example, 20,000 years ago, much of the United States was covered in glaciers. Credit: USGSĬlimate change describes a change in the average conditions - such as temperature and rainfall - in a region over a long period of time. Significant changes occurred in the 63 years between these two photos. Alaska's Muir glacier in August 1941 and August 2004.
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