SKYCALC Sky Model Calculator

Sky Model Mode Version 1.4.2
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SkyCalc Sky Model Calculator

Optional Parameter Initialisation using Almanac Service

All sky model parameters in the input form below can be set manually, but the time/coordinate dependent ones can be automatically initialised using this almanac service corresponding to a given time and sky position at the Paranal Observatory at geographic latitude −24°37'38".64 , longitude −70°24'17".64.

Date and UT time             h: m 
Target equatorial coordinates R.A. α= ° dec δ= °

The Cerro Paranal Advanced Sky Model

Altitude of Target above Horizon Alt= [19.5, 90]°       Alt and X are coupled through the
plane parallel approximation X=sec(z),
z being the zenith distance z=90°−Alt
Airmass X = [1, 3]
Season and Period of Night Season:
Night Period:
Precipitable Water Vapor PWV Seasonal Average (see above)
PWV = mm  (Paranal median ≈ 2.5mm)
Monthly Averaged Solar Flux s.f.u

Select Components to Include in the Radiance Model:

Scattered Moon Light
Note the following moon coordinate constraints: |z – zmoon| ≤ ρ ≤ |z + zmoon|
where ρ=moon/target separation, z=90°−target altitude and zmoon=90°−moon altitude.
Separation of Sun and Moon as seen from Earth [0,360]°; new=0°, [0°,180°]=waxing, full=180°, [180°,360°]=waning
Moon-Target Separation   ( ρ ) [0,180]°
Moon Altitude over Horizon [-90, 90]°
Moon-Earth Distance [0.91, 1.08], mean=1
Scattered Star Light
Zodiacal Light
Heliocentric Ecliptic Longitude of Target [-180, 180]°
Ecliptic Latitude of Target [-180, 180]°
Molecular Emission of Lower Atmosphere
Emission Lines of Upper Atmosphere
Airglow Continuum (Residual Continuum)

Thermal Emission
This radiance component represents an instrumental effect. The emission is provided relative to the other model components. To obtain the correct absolute flux, an instrumental response curve must be applied to the resulting model spectrum (see section 6.2.4 in the documentation).
Element1 (e.g. Telescope) T1 = K  Emissivity1 = [0,1[
Element2 (e.g. Instrument) T2 = K  Emissivity2 = [0,1[
Element3 (e.g. Cryostat) T3 = K  Emissivity3 = [0,1[

Wavelength Grid (in Vacuum)

Convolving Line Spread Function

λmin= nm [ ≥ 300 nm]
λmax= nm [ ≤ 30,000 nm]
Fixed Wavelength Step Δλ = nm/bin
Fixed Spectral Resolution R = λ/Δλ = [≤ 106]
Gaussian FWHM= bins
Boxcar Width= bins
Plot Radiance Spectrum
Plot Transmission Spectrum
Calculate Broad-Band UBVRIZYJHKLMNQ magnitudes per arcsec2
Plot LSF Kernel (select an LSF kernel to enable this option)


SkyCalc is based on the Cerro Paranal Advanced Sky Model, which was developed in particular to be used in the ESO Exposure Time Calculators, by a team of astronomers at the Institute for Astro- and Particle Physics at the University of Innsbruck, as part of an Austrian in-kind contribution to ESO.

The in-kind contribution also includes two tools to correct observations for telluric absorption and emission (Molecfit and Skycorr), which can be found here.

The citations for the Cerro Paranal Sky Model are Noll et al. (2012, A&A 543, A92) and Jones et al. (2013, A&A 560, A91).

A library of telluric transmission spectra with various resolutions and atmospheric conditions has been calculated with the Cerro Paranal Advanced Sky Model. A description of the usage of the spectra can be found in the article Moehler et al. (2014, A&A 568, A9).