## Time

Time has a measurement system which was originally based on natural events such as the time it takes for the earth to circle the sun, approximately one year.

### Units of Time

 The basic unit for time is the second. Time is not usually measured in multiples of 10. 1 minute = 60 seconds 1 hour = 60 minutes 1 day = 24 hours 1 week = 7 days 1 year = 12 months = 365.25 days

Months

The number of days in a month varies for historical reasons.

 Jan Feb March April May June July August Sep Oct Novr Dec 31 28* 31 30 31 30 31 31 30 31 30 31

*February has 29 days in Leap years, which as every 4 years (1992, 1996, 2000, 2004 ...)

Years

 10 years Decade 100 years Century 1000 years Millennium

### Daily Time

There are two systems for telling the time.

am and pm

• Times during the first 12 hours of the day (during the morning between midnight and midday) are followed by the letters am
• e.g. 3.42 am means 42 minutes after 3 o'clock in the morning.
• Times during the last 12 hours of the day (during the afternoon and evening between midday and midnight) are followed by the letters pm
• e.g. 5.26 pm means 26 minutes after 5 o'clock in the afternoon.

24-hour clock

The hours of the day are numbered from 0 to 24, starting with 0 as the first hour after midnight.

 e.g. 0047 means 47 minutes past midnight 0800 means 8 o'clock in the morning 1530 means half past three in the afternoon 2307 means 7 minutes after 11 o'clock at night Melbourne, Australia at about 2030 in winter

Special times

Midday is written 1200 or 12.00 pm or noon or midday and
Midnight is written 0000 or 12.00 am or midnight.

### Calculations involving Time

Typical calculations involving time include finding out how many minutes there are between two times or how many seconds there are in a number of days.

 Examples Answers Change 6 hours and 15 minutes into seconds 6 hours = 6 × 60 × 60 = 21 600 seconds 15 minutes = 15 × 60 = 900 seconds Total time = 22 500 seconds How many minutes are there between 7.35 am and 2.15pm the following day? From 7.35 am till 8.00 am = 25 minutes From 8.00 am till noon = 4 hours = 240 minutes From noon till 2. 00 pm = 2 hours = 120 minutes From 2.00 pm till 2.15 pm = 15 minutes Total time = 400 minutes