Calendars and Calculators

The tools and information linked from this page will be useful for all the aspects of observations that are related to the position of the target: their visibility, sun- and moon-rise and -set, ephemerides for Solar System minor bodies, etc.


  • Calculation of Site Sky Ephemerides
    This tool produces a nightime calendar of phenomena for a single site.
  • Solar System Ephemerides
    The JPL HORIZONS on-line solar system data and ephemeris computation service provides access to key solar system data and flexible production of highly accurate ephemerides for solar system objects.
  • Object Observability
    This tool provides object observability tables based on site, object coordinates and observing period.
  • Daily Almanac
    This tool produces almanac data for a single site and for a single date. Provided by courtesy of J. Thorstensen and B. Casey.
  • JD converter: Converts civil date to julian date and reverse

Position, Airmass, Extinction

  • Airmasses Calculator
    This tool provides hourly airmasses based on site, date, and object coordinates information. Additionally, it will compute the parallactic angle as well as heliocentric-barycentric corrections.
    • Plots: draw the airmass curves for a list of objects, for a given night
    • Extinction coefficients for La Silla (old Danish 1.54m page)
  • Differential athmospheric refraction table for the La Silla and Paranal sites.
    The differential atmospheric refraction is calculated in arcseconds, at an altitude of 2 km, as function of wavelength and airmass. A new calculator is being worked on and will go into the infrared.
  • Paralactic angle calculator
    While this tool has specific features for the DFOSC instrument on the 1.54m Danish telescope, it will compute the paralactic angle for any observations.

ETCs and Units Convertors