## Seconds

**Abbreviation/Symbol:**

arcsec

**Unit of:**

**Wordwide use:**

Seconds (angular) are a unit of measurement widely used worldwide in various fields, particularly in astronomy, navigation, and physics. This unit is primarily employed to measure angles, rotations, and angular velocities. One of the most common applications of seconds is in astronomy, where it is used to measure the apparent movement of celestial bodies across the sky. Astronomers use this unit to determine the positions of stars, planets, and other celestial objects accurately.

In navigation, seconds are crucial for determining the direction and orientation of a vessel or aircraft. By using this unit, navigators can calculate the angle between two points or the bearing of a specific location accurately. This information is vital for plotting courses, determining distances, and ensuring the safe navigation of ships and aircraft.

Seconds are also extensively used in physics, particularly in the study of rotational motion. This unit allows scientists to measure the angular displacement, angular velocity, and angular acceleration of objects undergoing rotational motion. By quantifying these parameters, physicists can analyze the behavior of rotating systems, such as spinning tops, rotating gears, or celestial bodies, and gain a deeper understanding of their dynamics.

**Definition:**

In the field of geometry and trigonometry, the term "seconds" refers to a unit of angular measurement. An angle is a geometric figure formed by two rays or lines that share a common endpoint, known as the vertex. The measurement of an angle is typically expressed in degrees, minutes, and seconds. While degrees and minutes are widely understood, seconds provide a more precise measurement of an angle.

A second, denoted by the symbol "″, is equal to 1/60th of a minute or 1/3600th of a degree. It is further divided into smaller units called milliseconds (ms), which are equal to 1/1000th of a second. The use of seconds in angular measurement allows for more accurate calculations and precise descriptions of angles, especially in fields such as astronomy, navigation, and engineering.

For example, when observing celestial bodies, astronomers often measure the angular separation between two objects using seconds. Similarly, in navigation, the direction of a ship or aircraft can be determined by measuring the angle between the object being observed and a reference point. The use of seconds in these applications ensures that measurements are as accurate as possible, enabling precise calculations and reliable results.

**Origin:**

The division of a circle into 360 degrees is believed to have originated in ancient Mesopotamia around 2000 BCE.

This division was likely influenced by the Sumerians' use of a sexagesimal (base-60) numeral system. The division of a degree into 60 minutes and a minute into 60 seconds was a natural extension of this system.

**Common references:**

The apparent size of the Moon is about 30 minutes of arc, which is equivalent to 1800 seconds.

In navigation, seconds are used to measure the angle between two objects, such as the angle between a ship and a lighthouse. This measurement, known as the bearing or azimuth, helps sailors determine their position and navigate accurately. By using a compass or other navigational tools, sailors can measure the angle in seconds and then use trigonometry to calculate their position.

In physics, seconds are used to measure the rate of rotation or angular velocity of objects. For example, the rotation of a spinning top or the movement of a pendulum can be measured in seconds per revolution. This measurement is crucial in understanding the dynamics and behavior of rotating systems.

**Usage context:**

Seconds as an angular measurement are used almost exclusively alongside minutes and degrees.