Units of Time
Time is defined as a continuous and ongoing sequence of events that occurs in irreversible succession, from the past, through the present and into the future. We measure time generally in seconds, minutes, hours, days and years by using clocks and calendars. A unit of time is basically measuring a duration by considering a particular time interval. There are so many units of time that we are going to know about in this article.
Units are time were based on movements of astronomical objects in the ancient world:
- Sun-based: Year was the time defined for the Earth to revolve around the Sun. Historically, the units of time based on this movement were – Olympiad (4 years), the lustrum (5 years), the indiction (15 years), the decade, the century and the millennium.
- Earth-based: Time is taken by the Earth to revolve around its own axis- sundial. Units used- week (7 days), fortnight (14 days). Day got divided into hours, minutes and seconds.
- Moon-based: Months were based on the orbital period of the moon around Earth.
- Celestial sphere-based: In sidereal times, the movement of constellations and stars were used to calculate the length of the year.
There are so many units of time that listing each and every one of them can be a tedious task as a lot of them are used only on rare occasions. So, here we will discuss the commonly used and some other useful units of time:
Different units of time:
- Potential use for scientific purposes
- Plank time: The amount of time taken by light to travel a plank length(5.39×10^-44 s).
- Yoktosecond: It is one septillionth of a second. (10^-24 s).
- Jiffy: It’s a unit of time mainly used in physics and is defined as the time taken by light to travel one fermi in a vacuum. (3×10^-24 s).
- Zeptosecond: It is one sextillionth of a second. It is also the time measurement scale of the NIST strontium atomic clock. The smallest fragment of time that can be currently measured is 247 zeptoseconds. (10^-21 s).
- Nanosecond: It is one billionth of a second (10^-9 s). It is also the time for molecules to fluoresce.
- Shake: It is a casual term used for a very short period of time. It is equal to 10 nanoseconds. (10^-8 s).
- Microsecond: It is one-millionth of a second. (10^-6 s). Symbol: µs.
- Human use
- Millisecond: It is one-thousandth of a second (10^-3 s). It is also the shortest time unit used on stopwatches.
- Centiseconds: One-hundredth of a second (10^-2 s).
- Second: It is the SI unit of time (1 s).
- Minute: 60 s.
- Moment: this unit was used in medieval times by astronomers to compute movements of astronomical bodies (90 s approximately).
- Hour: It consists of 60 minutes, 3600 seconds.
- Day: It is the longest unit on stopwatches and countdowns. (24 hrs).
- Week: A week consists of 7 days and in earlier times, it was also known as the “sennight”.
- Fortnight: It is made up of 2 weeks (14 days).
- Month: a month can consist of 28-31 days depending on different months.
- Quarter: Also known as season, made up of almost 3 months.
- Semester: It is basically a division of the academic year and consist of bout 18 weeks.
- Half-year: 6 months
- Year: A year is made up of 12 months (365 days).
- Leap Year: It comes after every third year and consists of 366 days.
- Decade: A decade is made up of 10 years.
- Jubilee: A silver jubilee consists of 25 years and golden jubilee consists of 50 years.
- Century: It consists of 100 years.
- Millennium: It is also known as “kiloannum”. It is made up of 1000 years.
- Astronomical use
- Galactic Year: It is the time taken by the solar system to orbit the centre of the milky way galaxy (about 230,000,000 years).
- Cosmological decade: It is ten times the length of the previous cosmological decade, with CÐ 1 beginning either 10 seconds or 10 years after the Big Bang, depending on the definition.
- Yottayottaanum: It is the biggest unit of time (about 1E+48 years= 10^48 years).