# Global Positioning System (GPS) epoch time

Global Positioning System (GPS) epoch time is a reference time used by the GPS system to measure time and determine the position of a GPS receiver. It is the time the GPS satellite clock count was set to zero, which is January 6, 1980, at 00:00:00 UTC. GPS epoch time is critical to the accuracy of GPS position calculations because it provides a reference time for GPS satellites and receivers to synchronize their clocks and calculate the time it takes for GPS signals to travel from the satellites to the receiver. This information is used to determine the precise location of the receiver.

The GPS epoch is also used as a reference time for GPS data collection and analysis. GPS data is usually recorded with respect to the GPS epoch, and the timestamps in GPS data files represent the number of seconds that have elapsed since the GPS epoch. This allows GPS data to be accurately synchronized and combined with other data sources using the GPS epoch as a reference time.

## GPS Clocks?

The clocks used in the GPS system are highly accurate atomic clocks, specifically, GPS satellites use atomic clocks based on the vibration of cesium atoms. These clocks are highly precise, and their rate of oscillation is used to measure time with great accuracy.

Each GPS satellite contains multiple atomic clocks, and they are continually monitored and corrected for any discrepancies. The accuracy of the clocks is critical to the overall accuracy of the GPS system, as any timing errors can result in incorrect location calculations.

On the other hand, GPS receivers used by the public typically have less accurate clocks than those used in GPS satellites. They often use quartz crystal clocks, which are less precise but still accurate enough for most applications. However, the receiver’s clock is still critical for calculating accurate location information, and GPS receivers continually adjust their internal clock to synchronize with the GPS satellite’s atomic clock signals.

## GPS epoch time FAQs

### What is GPS epoch time?

GPS epoch time is a reference time used by the Global Positioning System (GPS) to measure time and determine the position of a GPS receiver. It is defined as the time at which the GPS satellite clock count was set to zero, which is January 6, 1980, at 00:00:00 UTC.

### Why is GPS epoch time important?

GPS epoch time is important because it provides a reference time for GPS satellites and receivers to synchronize their clocks and calculate the time it takes for the GPS signals to travel from the satellites to the receiver. This information is used to determine the precise location of the receiver.

### How is GPS epoch time used to calculate GPS position?

GPS receivers use the time it takes for GPS signals to travel from multiple GPS satellites to calculate the receiver’s precise location. To do this, the receiver needs to know the precise time at which the signals were transmitted from the satellites. This is accomplished by comparing the time the signals were received by the receiver to the time the signals were transmitted by the satellite, as measured by the atomic clock on the satellite, and taking into account the time it took for the signals to travel from the satellite to the receiver. This calculation requires accurate synchronization of the clocks on the GPS satellites and the GPS receiver, which is achieved using GPS epoch time.

### How do I convert GPS epoch time to UTC time?

To convert a GPS epoch time to UTC time, you need to add the number of seconds that have elapsed since the GPS epoch time to the GPS epoch time and then adjust for any leap seconds that have been added to UTC time since the GPS epoch time. The formula for converting GPS epoch time to UTC time is: UTC time = GPS epoch time + (leap seconds + current time offset from GPS time) seconds.

### How accurate is GPS epoch time?

GPS epoch time is extremely accurate, with an uncertainty of only a few nanoseconds. This level of accuracy is achieved through the use of atomic clocks, which are extremely precise timekeeping devices.

### What is the difference between GPS time and UTC time?

GPS time is based on the same atomic clock standard as UTC time, but it does not include the leap seconds that are added to UTC time to account for the slowing of the Earth’s rotation. This means that GPS time runs ahead of UTC time by an amount equal to the number of leap seconds that have been added to UTC time.

### Why are leap seconds added to UTC time?

Leap seconds are added to UTC time to keep it in sync with the rotation of the Earth. The Earth’s rotation is slowing down slightly over time, which means that a day on Earth is getting longer. To keep the time of day in sync with the rotation of the Earth, leap seconds are added to UTC time periodically.

### How often are leap seconds added to UTC time?

Leap seconds are added to UTC time on an as-needed basis. They are typically added every 18-24 months, but the exact timing is determined by the International Earth Rotation and Reference Systems Service (IERS) based on the Earth’s rotation.

### How does GPS handle leap seconds?

GPS uses its own time standard, which is based on atomic clocks and does not include leap seconds. However, GPS receivers can convert GPS time to UTC time by adding the appropriate number of leap seconds.

### How do GPS receivers use GPS epoch time to determine location?

GPS receivers use the time it takes for GPS signals to travel from multiple GPS satellites to calculate the receiver’s precise location. To do this, the receiver needs to know the precise time at which the signals were transmitted from the satellites. This is accomplished by comparing the time the signals were received by the receiver to the time the signals were transmitted by