# Time

**temporaldurationsequence of eventsintervalstime frametime intervaltimeframeintervalperiodT**

Time is the indefinite continued progress of existence and events that occur in an apparently irreversible succession from the past, through the present, to the future.wikipedia

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### Future

**futuristicnear futurethe future**

Time is the indefinite continued progress of existence and events that occur in an apparently irreversible succession from the past, through the present, to the future.

The future is the time after the present.

### Present

**nowmodern dayreal time**

Time is the indefinite continued progress of existence and events that occur in an apparently irreversible succession from the past, through the present, to the future.

The present (or here and now) is the time that is associated with the events perceived directly and in the first time, not as a recollection (perceived more than once) or a speculation (predicted, hypothesis, uncertain).

### Derivative

**differentiationdifferentiablefirst derivative**

Time is a component quantity of various measurements used to sequence events, to compare the duration of events or the intervals between them, and to quantify rates of change of quantities in material reality or in the conscious experience.

For example, the derivative of the position of a moving object with respect to time is the object's velocity: this measures how quickly the position of the object changes when time advances.

### Event (philosophy)

**eventeventshistorical fact**

Time is the indefinite continued progress of existence and events that occur in an apparently irreversible succession from the past, through the present, to the future.

In philosophy, events are objects in time or instantiations of properties in objects.

### Clock

**timepiecemechanical clockanalog clock**

Time in physics is unambiguously operationally defined as "what a clock reads".

A clock is an instrument used to measure, keep, and indicate time.

### Past

**the past**

The concept of the past is derived from the linear fashion in which human observers experience time, and is accessed through memory and recollection.

### Calendar

**calendarscalendricalcalendar system**

Generally speaking, methods of temporal measurement, or chronometry, take two distinct forms: the calendar, a mathematical tool for organising intervals of time,

This is done by giving names to periods of time, typically days, weeks, months and years.

### Dimension

**dimensionsdimensionalone-dimensional**

Time is often referred to as a fourth dimension, along with three spatial dimensions.

In classical mechanics, space and time are different categories and refer to absolute space and time.

### International System of Quantities

**base quantitiesISQbase quantity**

Time is one of the seven fundamental physical quantities in both the International System of Units and International System of Quantities.

The International System of Quantities (ISQ) is a system based on seven base quantities: length, mass, time, electric current, thermodynamic temperature, amount of substance, and luminous intensity.

### Time value of money

**Cumulative average returndiscounted future returnsearning potential of money over time**

Time is also of significant social importance, having economic value ("time is money") as well as personal value, due to an awareness of the limited time in each day and in human life spans.

The time value of money explains why interest is paid or earned: interest, whether it is on a bank deposit or debt, compensates the depositor or lender for the time value of money.

### Time zone

**Sri Lanka Standard Time Zonetime zoneslocal time**

The position of the shadow marks the hour in local time.

Time zones tend to follow the boundaries of countries and their subdivisions instead of longitude, because it is convenient for areas in close commercial or other communication to keep the same time.

### Measuring instrument

**instrumentscientific instrumentinstruments**

A large variety of devices have been invented to measure time.

A physical system that exchanges energy may be described by the amount of energy exchanged per time-interval, also called power or flux of energy.

### Horology

**horologisthorologicalhorologists**

The study of these devices is called horology.

Horology ("the study of time", related to Latin horologium from Greek ὡρολόγιον, "instrument for telling the hour", from ὥρα hṓra "hour; time" and -o- interfix and suffix -logy) is the study of the measurement of time.

### Hourglass

**hour glasshour-glasssand timer**

The hourglass uses the flow of sand to measure the flow of time.

An hourglass (or sandglass, sand timer, or sand clock) is a device used to measure the passage of time.

### Time in physics

**timedurationnature of time**

Time in physics is unambiguously operationally defined as "what a clock reads".

The sun was the arbiter of the flow of time, but time was known only to the hour for millennia, hence, the use of the gnomon was known across most of the world, especially Eurasia, and at least as far southward as the jungles of Southeast Asia.

### Hour

**htime of dayhr**

A minute (min) is 60 seconds in length, and an hour is 60 minutes in length.

An hour (symbol: h; also abbreviated hr.) is a unit of time conventionally reckoned as 1⁄24 of a day and scientifically reckoned as 3,599–3,601 seconds, depending on conditions.

### Second

**ssecmegasecond**

The second (s) is the SI base unit.

The second (symbol: s, abbreviation: sec) is the base unit of time in the International System of Units (SI), commonly understood and historically defined as 1⁄86400 of a day – this factor derived from the division of the day first into 24 hours, then to 60 minutes and finally to 60 seconds each.

### Measurement

**measuremeasuringmeasurements**

Time is a component quantity of various measurements used to sequence events, to compare the duration of events or the intervals between them, and to quantify rates of change of quantities in material reality or in the conscious experience.

### Minkowski space

**Minkowski spacetimeMinkowski metricflat spacetime**

The current definition of the second, coupled with the current definition of the meter, is based on the special theory of relativity, which affirms our spacetime to be a Minkowski space.

In mathematical physics, Minkowski space (or Minkowski spacetime) is a combination of three-dimensional Euclidean space and time into a four-dimensional manifold where the spacetime interval between any two events is independent of the inertial frame of reference in which they are recorded.

### Minute

**minmmins.**

A minute (min) is 60 seconds in length, and an hour is 60 minutes in length.

The minute is a unit of time usually equal to 1⁄60 (the first sexagesimal fraction ) of an hour, or 60 seconds.

### Chronometry

**Chronometriquechronometerschronometric**

Generally speaking, methods of temporal measurement, or chronometry, take two distinct forms: the calendar, a mathematical tool for organising intervals of time,

Chronometry (from Greek χρόνος chronos, "time" and μέτρον metron, "measure") is the science of the measurement of time, or timekeeping.

### SI base unit

**base unitSI base unitsbase units**

The SI base unit for time is the SI second.

The units and their physical quantities are the second for time, the metre for measurement of length, the kilogram for mass, the ampere for electric current, the kelvin for temperature, the mole for amount of substance, and the candela for luminous intensity.

### Physical quantity

**physical quantitiesquantitiesquantity**

Time is a component quantity of various measurements used to sequence events, to compare the duration of events or the intervals between them, and to quantify rates of change of quantities in material reality or in the conscious experience. Time is one of the seven fundamental physical quantities in both the International System of Units and International System of Quantities.

### Solar time

**mean solar timesolar dayapparent solar time**

The Mean Solar Time system defines the second as 1/86,400 of the mean solar day, which is the year-average of the solar day. Unlike solar time, which is relative to the apparent position of the Sun, sidereal time is the measurement of time relative to that of a distant star.

Solar time is a calculation of the passage of time based on the position of the Sun in the sky.

### Position of the Sun

**Sun's positionpositiondeclination**

Unlike solar time, which is relative to the apparent position of the Sun, sidereal time is the measurement of time relative to that of a distant star.

The position of the Sun in the sky is a function of both the time and the geographic location of observation on Earth's surface.