Getting Started

This documentation is intended to explain how to compute time conversions and offsets using timescale.

Time

The time module within timescale can convert different time formats to the necessary time format of a given program. The time module can also parse date strings describing the units and epoch of relative times, or the calendar date of measurement for geotiff formats. timescale keeps updated tables of leap seconds for converting from GPS, LORAN and TAI times.

  • TAI time: International Atomic Time which is computed as the weighted average of several hundred atomic clocks.

  • UTC time: Coordinated Universal Time which is periodically adjusted to account for the difference between the definition of the second and the rotation of Earth.

  • GPS time: Atomic timing system for the Global Positioning System constellation of satellites monitored by the United States Naval Observatory (USNO). GPS time and UTC time were equal on January 6, 1980. TAI time is ahead of GPS time by 19 seconds.

  • LORAN time: Atomic timing system for the Loran-C chain transmitter sites used in terrestrial radionavigation. LORAN time and UTC time were equal on January 1, 1958. TAI time is ahead of LORAN time by 10 seconds.

timescale also keeps updated tables of delta times for converting between dynamic (TT) and universal (UT1) times. Delta times (TT - UT1) are the differences between Dynamic Time (TT) and Universal Time (UT1) [7]. Universal Time (UT1) is based on the rotation of the Earth, which varies irregularly, and so UT1 is adjusted periodically. Dynamic Time (TT) is a uniform, monotonically increasing time standard based on atomic clocks that is used for the accurate calculation of celestial mechanics, orbits and ephemerides. Delta times can be added to Universal Time (UT1) values to convert to Dynamic Time (TT) values.

Programs

Timescale objects can be used to convert between date and time formats. There are a few different ways to create a Timescale object:

  1. range of dates

import timescale.time
ts = timescale.from_range('2018-01-01','2018-12-31', 1)

  1. delta times

import numpy as np
import timescale.time
delta_time = np.arange(365)*timescale.time._to_sec['day']
ts = timescale.from_deltatime(delta_time, epoch=(2018,1,1,0,0,0))

  1. datetime objects

import datetime
import timescale.time
date = datetime.datetime(2018,1,1,0,0,0)
ts = timescale.from_datetime(date)

  1. calendar dates

import numpy as np
import timescale.time
year = 2018
month = 1
day = 1 + np.arange(31)
ts = timescale.from_calendar(year, month, day)

  1. Julian dates

import numpy as np
import timescale.time
JD = np.arange(2458119.5, 2458150.5, 1)
ts = timescale.from_julian(JD)

Timescale objects can be used to convert epochs, convert to different time standards, convert to datetime arrays, and other time conversions.

Tip

See the API Reference for more information.