A
What is Attoseconds (as)?
Answer: An attosecond (as) is one-quintillionth of a second (10⁻¹⁸). It is so incredibly short that more attoseconds fit into a single second than seconds fit into the entire age of the universe. Attoseconds are mostly used in advanced physics and quantum mechanics, particularly for observing the movement of electrons inside atoms. The development of attosecond science has allowed scientists to explore phenomena that were previously beyond the reach of measurement, such as electron dynamics during chemical reactions or the behavior of light on the quantum level.
B
C
What is Centuries (cent)?
Answer: A century (cent) is a period of 100 years. It is widely used to divide history into eras and to describe cultural, political, and technological transformations that unfold over long spans of time. For example, the 20th century was marked by world wars, the space race, and the digital revolution, while the 21st century has already seen advances in artificial intelligence and globalization. Centuries help us organize human progress and provide perspective on how civilizations evolve over generations.
D
What is Days (d)?
Answer: A day (d) is the time it takes for Earth to complete one full rotation on its axis, which is approximately 24 hours. Days are the most natural unit of time in human life, connected directly to the cycle of light and darkness. They regulate sleep, work, biological rhythms, and cultural activities. From ancient sundials to modern atomic clocks, the measurement of days has remained central to how humans experience and organize life.
What is Decades (dec)?
Answer: A decade (dec) equals 10 years. It is often used to analyze social trends, historical movements, or generational shifts. For example, the 1960s are remembered for counterculture, civil rights movements, and space exploration, while the 1990s were defined by globalization, the rise of the internet, and pop culture icons. Decades provide a way to capture the “spirit of an era” and compare changes across time.
E
What is Exaseconds (Es)?
Answer: An exasecond (Es) is one quintillion seconds (10¹⁸). To understand how vast this is, one exasecond equals about 31.7 billion years, which is more than twice the estimated age of the universe. Exaseconds are used in astrophysics and cosmology to describe events and processes that happen on unimaginably long timescales, such as the life cycles of galaxies or the long-term fate of the cosmos.
F
What is Femtoseconds (fs)?
Answer: A femtosecond (fs) is one quadrillionth of a second (10⁻¹⁵). This unit is essential in laser science, where pulses of light lasting just a few femtoseconds can be used to track chemical reactions as they happen. Scientists have won Nobel Prizes for developing femtosecond laser technology because it allows the observation of atomic-level processes like bond formation and breaking, which occur faster than the blink of an eye by many orders of magnitude.
What is Fortnights (fn)?
Answer: A fortnight (fn) equals 14 days, or two weeks. Historically common in British English, it was used in law, business, and culture as a standard short-term period. Even today, in some countries, people still receive wages or plan events “fortnightly.” Though less common in global usage, it remains a useful bridge between a week and a month.
G
What is Gigaseconds (Gs)?
Answer: A gigasecond (Gs) equals one billion seconds (10⁹). This amounts to about 31.7 years, which is roughly one-third of an average human lifespan. Gigaseconds are particularly useful in scientific disciplines for describing durations that are too large for minutes or days but too short for geologic or cosmic scales, such as human lifetimes in seconds or planetary orbital cycles.
What is Gigayear (Ga)?
Answer: A gigayear (Ga) is one billion years. This timescale is most often used in geology, paleontology, and astronomy. For example, Earth is estimated to be about 4.5 Ga old, while the universe is approximately 13.8 Ga in age. Gigayears provide a necessary framework for studying evolution, tectonics, and cosmic history.
What is Galactic Year (Gy)?
Answer: A galactic year (Gy) is the time it takes the Solar System to orbit once around the Milky Way galaxy. This journey takes between 225 and 250 million Earth years. Astronomers use this concept to place Earth’s history in a galactic context, such as noting how many galactic years have passed since the dinosaurs lived.
H
What is Hours (h)?
Answer: An hour (h) equals 60 minutes or 3,600 seconds. Hours divide the day into manageable units for work, rest, and cultural activity. The concept of hours originates from ancient civilizations like the Egyptians, who divided daylight into 12 parts. Today, hours remain essential in almost every aspect of life, from scheduling to scientific measurement.
I
J
What is Julian Year (jy)?
Answer: A Julian year (jy) is defined as exactly 365.25 days, reflecting the calendar introduced by Julius Caesar in 45 BCE. While the Gregorian calendar later replaced it, the Julian year is still used in astronomy for precise calculations, especially when studying celestial motion or long-term astronomical events.
K
What is Kiloseconds (ks)?
Answer: A kilosecond (ks) equals 1,000 seconds, or about 16.7 minutes. Although it is not commonly used in daily life, scientists and engineers use kiloseconds when working with timescales larger than minutes but smaller than hours, such as countdowns in space missions or controlled experiments.
L
M
What is Milliseconds (ms)?
Answer: A millisecond (ms) is one-thousandth of a second (10⁻³). This unit is extremely important in technology, gaming, and computing where system response times and network speeds are often measured in milliseconds. Human reflexes also fall within this timescale, making it a natural point of reference when testing performance and reaction.
What is Microseconds (μs)?
Answer: A microsecond (μs) is one-millionth of a second (10⁻⁶). Events at this scale are much faster than human perception and are used to measure the speed of computer processors, telecommunications signals, and certain biological processes. For example, the time taken for an electrical impulse to travel through a neuron can be measured in microseconds.
What is Minutes (min)?
Answer: A minute (min) equals 60 seconds. Minutes are one of the most familiar units of time, widely used for scheduling, communication, and planning. They act as a bridge between short and long durations, giving structure to daily life and helping synchronize human activities across the world.
What is Months (mo)?
Answer: A month (mo) is a traditional unit originally based on the phases of the Moon. In modern calendars, months are standardized to 28–31 days. They are crucial for organizing years into manageable divisions, guiding agriculture, religious observances, and cultural traditions throughout history.
What is Millennia (mil)?
Answer: A millennium (mil) equals 1,000 years. Millennia are often used to describe the grand sweep of civilizations and historical epochs. For instance, the first millennium CE saw the rise and fall of empires like Rome, while the second millennium witnessed global exploration, industrialization, and the digital revolution.
What is Megaseconds (Ms)?
Answer: A megasecond (Ms) is one million seconds, which equals about 11.6 days. It is a useful scientific measure for time intervals too long for hours or days but shorter than months. Megaseconds are often applied in scientific experiments, astronomy, or space travel studies where longer timescales need precision.
What is Megayear (Ma)?
Answer: A megayear (Ma) equals one million years. Geologists and paleontologists use it to describe processes like continental drift, mountain building, or evolutionary changes in species. The age of fossils and rocks is often given in megayears, offering perspective on Earth’s deep past.
N
What is Nanoseconds (ns)?
Answer: A nanosecond (ns) is one-billionth of a second (10⁻⁹). At this timescale, light can only travel about 30 centimeters. Nanoseconds are used in computer engineering, high-frequency trading, and particle physics. For example, the delay between pressing a keyboard key and registering the input can be measured in nanoseconds.
O
P
What is Picoseconds (ps)?
Answer: A picosecond (ps) is one-trillionth of a second (10⁻¹²). At this scale, light only travels a fraction of a millimeter. Scientists use picoseconds to study ultrafast phenomena such as molecular vibrations, chemical reactions, and laser pulses that are far too quick for the human eye.
What is Petaseconds (Ps)?
Answer: A petasecond (Ps) equals one quadrillion seconds (10¹⁵). This massive timescale is far beyond human experience, equaling more than 31 million years. Petaseconds are most relevant in astrophysics, where they may be used to describe stellar or galactic lifetimes.
What is Planck Time (tP)?
Answer: Planck time (tP) is the smallest meaningful unit of time in physics, approximately 5.39 × 10⁻⁴⁴ seconds. It represents the scale at which conventional physics breaks down and quantum gravity dominates. Below this timescale, current scientific theories cannot accurately describe what happens, making it a fundamental boundary in physics.
Q
R
S
What is Seconds (s)?
Answer: A second (s) is the base unit of time in the International System of Units (SI). It is defined by the precise vibrations of a cesium-133 atom: 9,192,631,770 cycles per second. Seconds underpin all modern timekeeping systems and are used in everyday activities, science, and technology. They form the foundation upon which minutes, hours, and longer timescales are built.
What is Sidereal Day (sd)?
Answer: A sidereal day (sd) is the time it takes Earth to rotate once relative to the stars rather than the Sun. It lasts about 23 hours, 56 minutes, and 4 seconds. Astronomers use the sidereal day to track celestial objects more accurately, as it reflects Earth’s true rotational period.
What is Sidereal Year (sy)?
Answer: A sidereal year (sy) is the time Earth takes to orbit the Sun relative to distant stars, lasting about 365.256 days. It differs slightly from the tropical year (which defines the calendar year) due to the precession of Earth’s axis. This distinction is crucial in astronomy for long-term star mapping.
What is Shakes (sh)?
Answer: A shake (sh) is an informal unit equal to 10 nanoseconds. It originated in nuclear physics during the Manhattan Project to measure reaction times in atomic processes. Today, it is sometimes used in computing and engineering as a convenient term for extremely short durations.
T
What is Teraseconds (Ts)?
Answer: A terasecond (Ts) equals one trillion seconds (10¹²), or about 31,700 years. Such a timescale is useful in archaeology, geology, and astronomy, providing a bridge between human history and deep time. For example, the entire recorded history of civilization is only a small fraction of a terasecond.
U
V
W
What is Weeks (wk)?
Answer: A week (wk) is a unit of time equal to 7 days. Weeks structure calendars worldwide, guiding religious practices, business schedules, and cultural traditions. The seven-day cycle dates back thousands of years to ancient civilizations that observed lunar and planetary movements.
X
Y
What is Years (yr)?
Answer: A year (yr) is the time Earth takes to orbit the Sun once, about 365.25 days. Years are essential for tracking seasons, planning agriculture, and marking human life stages such as birthdays and anniversaries. In science, years provide a framework for recording historical and geological events.
What is Yottaseconds (Ys)?
Answer: A yottasecond (Ys) equals one septillion seconds (10²⁴). This scale surpasses the age of stars, galaxies, and even the universe itself. While it is mostly theoretical, yottaseconds provide scientists with a way to conceptualize unimaginably vast cosmic durations.
Z
What is Zeptoseconds (zs)?
Answer: A zeptosecond (zs) is one sextillionth of a second (10⁻²¹). It represents one of the shortest measurable times ever observed. Scientists use zeptoseconds to measure the speed of light crossing molecules, capturing events at the edge of quantum physics.
What is Zettaseconds (Zs)?
Answer: A zettasecond (Zs) equals one sextillion seconds (10²¹). This unit is far beyond any human experience but may be applied in astrophysics and cosmology when describing the lifespans of stars or the evolution of galaxies on unimaginable scales.