Tempo is a software program used to analyze radio observations of pulsar

Pulsar

A pulsar is a highly magnetized, rotating neutron star that emits a beam of electromagnetic radiation. The radiation can only be observed when the beam of emission is pointing towards the Earth. This is called the lighthouse effect and gives rise to the pulsed nature that gives pulsars their name...

s. Once enough observations are available, Tempo can deduce the pulsar rotation rate and phase, astrometric position and rates of change, and parameters of binary systems

Binary system (astronomy)

A binary system is an astronomical term referring to two objects in space which are so close that their gravitational interaction causes them to orbit about a common center of mass. Some definitions A binary system is an astronomical term referring to two objects in space (usually stars, but also...

, by fitting models to pulse times of arrival measured at one or more terrestrial observatories. This is a non-trivial procedure because much larger effects must be removed before the detailed fit can be performed. These include:

• Dispersion of the pulses in the Interstellar medium, the solar system, and the ionosphere
  Ionosphere
  The ionosphere is a part of the upper atmosphere, comprising portions of the mesosphere, thermosphere and exosphere, distinguished because it is ionized by solar radiation. It plays an important part in atmospheric electricity and forms the inner edge of the magnetosphere...
  
  
• Observatory motion (including Earth rotation, precession
  Precession
  Precession is a change in the orientation of the rotation axis of a rotating body. It can be defined as a change in direction of the rotation axis in which the second Euler angle is constant...
  
  , nutation
  Nutation
  Nutation is a rocking, swaying, or nodding motion in the axis of rotation of a largely axially symmetric object, such as a gyroscope, planet, or bullet in flight, or as an intended behavior of a mechanism...
  
  , polar motion
  Polar motion
  Polar motion of the earth is the movement of Earth's rotational axis across its surface. This is measured with respect to a reference frame in which the solid Earth is fixed...
  
   and orbital motion)
• Tropospheric propagation
  Tropospheric propagation
  Tropospheric propagation describes electromagnetic propagation in relation to the troposphere.The service area from a television or frequency modulated radio transmitter extends to just beyond the optical horizon, at which point signals start to rapidly reduce in strength...
  
   delay
• Gravitational time dilation
  Gravitational time dilation
  Gravitational time dilation is the effect of time passing at different rates in regions of different gravitational potential; the lower the gravitational potential, the more slowly time passes...
  
   due to binary companions and Solar system bodies.

Tempo is maintained and distributed by Princeton University

Princeton University

Princeton University is a private research university located in Princeton, New Jersey, United States. The school is one of the eight universities of the Ivy League, and is one of the nine Colonial Colleges founded before the American Revolution....

 and the Australia Telescope National Facility

Australia Telescope National Facility

The Commonwealth Scientific and Industrial Research Organisation 's radio astronomy observatories are collectively known as the Australia Telescope National Facility , with the facility supporting Australia's research in radio astronomy....

. There is a reference manual available, but no general documentation.

Tempo is a relatively old program, and is being replaced by Tempo2. The main advantages of Tempo2, from the abstract, are:

We have developed tempo2, a new pulsar timing package that contains propagation and other relevant effects implemented at the 1ns level of precision (a factor of ~100 more precise than previously obtainable). In contrast with earlier timing packages, tempo2 is compliant with the general relativistic framework of the IAU 1991 and 2000 resolutions and hence uses the International Celestial Reference System, Barycentric Coordinate Time and up-to-date precession, nutation and polar motion models.