Skybright Class Reference

This class makes use of the 1998 sky brightness model by Bradley Schaefer. More...

#include <Skybright.hpp>

Public Member Functions
	Skybright ()
	Constructor.
void	setDate (const int year, const int month, const float moonPhase, const float moonMag)
	Set the sky date to use for atmosphere computation. More...
void	setLocation (const float latitude, const float altitude, const float temperature=15.f, const float relativeHumidity=40.f)
	Set the position parameters to use for atmosphere computation. More...
void	setSunMoon (const float cosDistMoonZenith, const float cosDistSunZenith)
	Set the moon and sun zenith angular distance (cosin given) and precompute what can be This function has to be called once before any call to getLuminance() More...
float	getLuminance (float cosDistMoon, const float cosDistSun, const float cosDistZenith) const
	Compute the luminance at the given position. More...

Detailed Description

Further reading:

• B. Schaefer: Sky&Telescope 4/1987
• B. Schaefer: Astronomy and the Limits of Vision. Vistas in Astronomy 36, 311-361, 1993.
• B. Schaefer: To the Visual Limits. Sky&Telescope 5/1998 57-60.
• B. Schaefer: Archaeoastronomy XV, 2000.

TASKS TO IMPROVE: Some components of the Schaefer model as given in BASIC sourcecode in the 1998 S&T article are strongly simplified. E.g.,

• setDate should be taken always in the Gregorian Calendar, or circumvented altogether:
• RA takes the right ascension of the sun. --> Could be replaced with the proper value!
• bNightTerm includes an 11.0-year solar cycle, and will be erratic a few cycles from 1992. --> At least find a more accurate average period.
• Extinction could make use of the K computed in SetLocation. But first re-verify that the code here really follows the Schaefer model (with obvious amendments).

Compute the luminance of the sky according to some parameters like sun moon position or time or altitude etc...

Member Function Documentation

getLuminance()

float Skybright::getLuminance	(	float	cosDistMoon,
		const float	cosDistSun,
		const float	cosDistZenith
	)		const

Parameters

cosDistMoon	cos(angular distance between moon and the position)
cosDistSun	cos(angular distance between sun and the position)
cosDistZenith	cos(angular distance between zenith and the position)

setDate()

void Skybright::setDate	(	const int	year,
		const int	month,
		const float	moonPhase,
		const float	moonMag
	)

Parameters

year	the year in YYYY format
month	the month: 1=Jan, 12=Dec
moonPhase	the moon phase in radian 0=Full Moon, PI/2=First Quadrant/Last Quadran, PI=No Moon
moonMag	visual magnitude of the moon. Could be computed from geometry, but in case of eclipses we should deliver it here.

setLocation()

void Skybright::setLocation	(	const float	latitude,
		const float	altitude,
		const float	temperature = 15.f,
		const float	relativeHumidity = 40.f
	)

Parameters

latitude	observer latitude in radian
altitude	observer altitude in m
temperature	temperature in deg. C
relativeHumidity	air humidity in %

setSunMoon()

void Skybright::setSunMoon	(	const float	cosDistMoonZenith,
		const float	cosDistSunZenith
	)

Parameters

cosDistMoonZenith	cos(angular distance between moon and zenith)
cosDistSunZenith	cos(angular distance between sun and zenith)