SkyPoint Class Reference

The sky coordinates of a point in the sky. More...

#include <skypoint.h>

Inheritance diagram for SkyPoint:

[legend]

List of all members.

Public Member Functions
void	aberrate (const KSNumbers *num)
void	addEterms (void)
const dms *	alt () const
dms	angularDistanceTo (SkyPoint *sp)
void	apparentCoord (long double jd0, long double jdf)
const dms *	az () const
void	B1950ToJ2000 (void)
QString	constellation (QPtrList< CSegment > &seglist, QPtrList< SkyObject > &cnames) const
const dms *	dec () const
const dms *	dec0 () const
void	EclipticToEquatorial (const KSNumbers *num)
void	Equatorial1950ToGalactic (dms &galLong, dms &galLat)
void	EquatorialToEcliptic (const KSNumbers *num)
void	EquatorialToHorizontal (const dms *LST, const dms *lat)
SkyPoint	Eterms (void)
void	findEcliptic (const dms *Obliquity, dms &EcLong, dms &EcLat)
void	GalacticToEquatorial1950 (const dms *galLong, const dms *galLat)
void	HorizontalToEquatorial (const dms *LST, const dms *lat)
void	J2000ToB1950 (void)
void	nutate (const KSNumbers *num)
bool	operator== (SkyPoint &p)
void	precessFromAnyEpoch (long double jd0, long double jdf)
const dms *	ra () const
const dms *	ra0 () const
void	set (double r, double d)
void	set (const dms *r, const dms *d)
void	set (const dms &r, const dms &d)
void	setAlt (double alt)
void	setAlt (dms alt)
void	setAz (double az)
void	setAz (dms az)
void	setDec (double d)
void	setDec (dms d)
void	setDec0 (double d)
void	setDec0 (dms d)
void	setFromEcliptic (const dms *Obliquity, const dms *EcLong, const dms *EcLat)
void	setRA (double r)
void	setRA (dms r)
void	setRA0 (double r)
void	setRA0 (dms r)
	SkyPoint (double r=0.0, double d=0.0)
	SkyPoint (const dms *r, const dms *d)
	SkyPoint (const dms &r, const dms &d)
void	subtractEterms (void)
virtual void	updateCoords (KSNumbers *num, bool includePlanets=true, const dms *lat=0, const dms *LST=0)
double	vGeocentric (double vhelio, long double jd)
double	vGeoToVHelio (double vgeo, long double jd)
double	vHeliocentric (double vlsr, long double jd)
double	vHelioToVlsr (double vhelio, long double jd)
double	vREarth (long double jd0)
double	vRSite (double vsite[3])
double	vRSun (long double jd)
double	vTopocentric (double vgeo, double vsite[3])
double	vTopoToVGeo (double vtopo, double vsite[3])
virtual	~SkyPoint ()
Protected Member Functions
void	precess (const KSNumbers *num)

---

Detailed Description

The sky coordinates of a point in the sky.

The coordinates are stored in both Equatorial (Right Ascension, Declination) and Horizontal (Azimuth, Altitude) coordinate systems. Provides set/get functions for each coordinate angle, and functions to convert between the Equatorial and Horizon coordinate systems.

Because the coordinate values change slowly over time (due to precession, nutation), the "catalog coordinates" are stored (RA0, Dec0), which were the true coordinates on Jan 1, 2000. The true coordinates (RA, Dec) at any other epoch can be found from the catalog coordinates using updateCoords(). Stores dms coordinates for a point in the sky. for converting between coordinate systems.

Author:

Jason Harris

Version:

1.0

Definition at line 51 of file skypoint.h.

---

Constructor & Destructor Documentation

SkyPoint::SkyPoint	(	const dms &	r,
		const dms &	d
	)			[inline]

Default constructor: Sets RA, Dec and RA0, Dec0 according to arguments.

Does not set Altitude or Azimuth.

Parameters:

	r	Right Ascension
	d	Declination

Definition at line 58 of file skypoint.h.

SkyPoint::SkyPoint	(	const dms *	r,
		const dms *	d
	)			[inline]

Alternate constructor using pointer arguments, for convenience.

It behaves essentially like the default constructor.

Parameters:

	r	Right Ascension pointer
	d	Declination pointer

Definition at line 65 of file skypoint.h.

SkyPoint::SkyPoint	(	double	r = 0.0,
		double	d = 0.0
	)			[inline]

Alternate constructor using double arguments, for convenience.

It behaves essentially like the default constructor.

Parameters:

	r	Right Ascension, expressed as a double
	d	Declination, expressed as a double

Definition at line 72 of file skypoint.h.

SkyPoint::~SkyPoint

(

)

[virtual]

Empty destructor.

Definition at line 43 of file skypoint.cpp.

---

Member Function Documentation

void SkyPoint::aberrate

(

const KSNumbers *

num

)

Determine the effects of aberration for this SkyPoint.

Parameters:

num

pointer to KSNumbers object containing current values of time-dependent variables.

Definition at line 206 of file skypoint.cpp.

void SkyPoint::addEterms

(

void

)

Coordinates in the FK4 catalog include the effect of aberration due to the ellipticity of the orbit of the Earth.

Coordinates in the FK5 catalog do not include these terms. In order to convert from B1950 (FK4) to actual mean places one has to use this function.

Definition at line 503 of file skypoint.cpp.

const dms* SkyPoint::alt

(

)

const [inline]

Returns:

a pointer to the current Altitude.

Definition at line 218 of file skypoint.h.

dms SkyPoint::angularDistanceTo

(

SkyPoint *

sp

)

Computes the angular distance between two SkyObjects.

The algorithm to compute this distance is: cos(distance) = sin(d1)*sin(d2) + cos(d1)*cos(d2)*cos(a1-a2) where a1,d1 are the coordinates of the first object and a2,d2 are the coordinates of the second object. However this algorithm is not accurate when the angular separation is small. Meeus provides a different algorithm in page 111 which we implement here.

Parameters:

sp

SkyPoint to which distance is to be calculated

Returns:

dms angle representing angular separation.

Definition at line 520 of file skypoint.cpp.

void SkyPoint::apparentCoord	(	long double	jd0,
		long double	jdf
	)

Computes the apparent coordinates for this SkyPoint for any epoch, accounting for the effects of precession, nutation, and aberration.

No descriptions.

Similar to updateCoords(), but the starting epoch need not be J2000, and the target epoch need not be the present time.

Parameters:

	jd0	Julian Day which identifies the original epoch
	jdf	Julian Day which identifies the final epoch

Definition at line 332 of file skypoint.cpp.

const dms* SkyPoint::az

(

)

const [inline]

Returns:

a pointer to the current Azimuth.

Definition at line 214 of file skypoint.h.

void SkyPoint::B1950ToJ2000

(

void

)

Exact precession from Besselian epoch 1950 to epoch J2000.

The coordinates referred to the first epoch are in the FK4 catalog, while the latter are in the Fk5 one. Reference: Smith, C. A.; Kaplan, G. H.; Hughes, J. A.; Seidelmann, P. K.; Yallop, B. D.; Hohenkerk, C. Y. Astronomical Journal, vol. 97, Jan. 1989, p. 265-279 This transformation requires 4 steps:

• Correct E-terms
• Precess from B1950 to 1984, January 1st, 0h, using Newcomb expressions
• Add zero point correction in right ascension for 1984
• Precess from 1984, January 1st, 0h to J2000

Definition at line 387 of file skypoint.cpp.

QString SkyPoint::constellation	(	QPtrList< CSegment > &	seglist,
		QPtrList< SkyObject > &	cnames
	)			const

Definition at line 540 of file skypoint.cpp.

const dms* SkyPoint::dec

(

)

const [inline]

Returns:

a pointer to the current Declination.

Definition at line 210 of file skypoint.h.

const dms* SkyPoint::dec0

(

)

const [inline]

Returns:

a pointer to the catalog Declination.

Definition at line 202 of file skypoint.h.

void SkyPoint::EclipticToEquatorial

(

const KSNumbers *

num

)

Convert Ecliptic logitude/latitude to Right Ascension/Declination.

void SkyPoint::Equatorial1950ToGalactic	(	dms &	galLong,
		dms &	galLat
	)

Computes galactic coordinates from equatorial coordinates referred to epoch 1950.

RA and Dec are, therefore assumed to be B1950 coordinates.

Definition at line 344 of file skypoint.cpp.

void SkyPoint::EquatorialToEcliptic

(

const KSNumbers *

num

)

Convert Right Ascension/Declination to Ecliptic logitude/latitude.

void SkyPoint::EquatorialToHorizontal	(	const dms *	LST,
		const dms *	lat
	)

Determine the (Altitude, Azimuth) coordinates of the SkyPoint from its (RA, Dec) coordinates, given the local sidereal time and the observer's latitude.

Returns:

a pointer to the current galactic latitude.

a pointer to the current galactic longitude.

Parameters:

	LST	pointer to the local sidereal time
	lat	pointer to the geographic latitude

Definition at line 46 of file skypoint.cpp.

SkyPoint SkyPoint::Eterms

(

void

)

Determine the E-terms of aberration In the past, the mean places of stars published in catalogs included the contribution to the aberration due to the ellipticity of the orbit of the Earth.

These terms, known as E-terms were almost constant, and in the newer catalogs (FK5) are not included. Therefore to convert from FK4 to FK5 one has to compute these E-terms.

Definition at line 486 of file skypoint.cpp.

void SkyPoint::findEcliptic	(	const dms *	Obliquity,
		dms &	EcLong,
		dms &	EcLat
	)

Determine the Ecliptic coordinates of the SkyPoint, given the Julian Date.

The ecliptic coordinates are returned as reference arguments (since they are not stored internally)

Definition at line 107 of file skypoint.cpp.

void SkyPoint::GalacticToEquatorial1950	(	const dms *	galLong,
		const dms *	galLat
	)

Computes equatorial coordinates referred to 1950 from galactic ones referred to epoch B1950.

RA and Dec are, therefore assumed to be B1950 coordinates.

Definition at line 364 of file skypoint.cpp.

void SkyPoint::HorizontalToEquatorial	(	const dms *	LST,
		const dms *	lat
	)

Determine the (RA, Dec) coordinates of the SkyPoint from its (Altitude, Azimuth) coordinates, given the local sidereal time and the observer's latitude.

Parameters:

	LST	pointer to the local sidereal time
	lat	pointer to the geographic latitude

Definition at line 72 of file skypoint.cpp.

void SkyPoint::J2000ToB1950

(

void

)

Exact precession from epoch J2000 Besselian epoch 1950.

The coordinates referred to the first epoch are in the FK4 catalog, while the latter are in the Fk5 one. Reference: Smith, C. A.; Kaplan, G. H.; Hughes, J. A.; Seidelmann, P. K.; Yallop, B. D.; Hohenkerk, C. Y. Astronomical Journal, vol. 97, Jan. 1989, p. 265-279 This transformation requires 4 steps:

• Precess from J2000 to 1984, January 1st, 0h
• Add zero point correction in right ascension for 1984
• Precess from 1984, January 1st, 0h, to B1950 using Newcomb expressions
• Correct E-terms

Definition at line 435 of file skypoint.cpp.

void SkyPoint::nutate

(

const KSNumbers *

num

)

Determine the effects of nutation for this SkyPoint.

Parameters:

num

pointer to KSNumbers object containing current values of time-dependent variables.

Definition at line 177 of file skypoint.cpp.

bool SkyPoint::operator==

(

SkyPoint &

p

)

[inline]

Definition at line 390 of file skypoint.h.

void SkyPoint::precess

(

const KSNumbers *

num

)

[protected]

Precess this SkyPoint's catalog coordinates to the epoch described by the given KSNumbers object.

Parameters:

num

pointer to a KSNumbers object describing the target epoch.

Definition at line 147 of file skypoint.cpp.

void SkyPoint::precessFromAnyEpoch	(	long double	jd0,
		long double	jdf
	)

General case of precession.

It precess from an original epoch to a final epoch. In this case RA0, and Dec0 from SkyPoint object represent the coordinates for the original epoch and not for J2000, as usual.

Parameters:

	jd0	Julian Day which identifies the original epoch
	jdf	Julian Day which identifies the final epoch

Definition at line 248 of file skypoint.cpp.

const dms* SkyPoint::ra

(

)

const [inline]

Returns:

a pointer to the current Right Ascension.

Definition at line 206 of file skypoint.h.

const dms* SkyPoint::ra0

(

)

const [inline]

Sets Galactic Longitude.

Parameters:

	glo	Galactic Longitude.Overloaded member function, provided for convenience. It behaves essentially like the above function.
	glo	Galactic Longitude, expressed as a double.Sets Galactic Longitude.
	gla	Galactic Longitude.Overloaded member function, provided for convenience. It behaves essentially like the above function.
	gla	Galactic Longitude, expressed as a double.

Returns:

a pointer to the catalog Right Ascension.

Definition at line 198 of file skypoint.h.

void SkyPoint::set	(	double	r,
		double	d
	)

Overloaded member function, provided for convenience.

It behaves essentially like the above function.

Parameters:

	r	Right Ascension
	d	Declination

Definition at line 36 of file skypoint.cpp.

void SkyPoint::set	(	const dms *	r,
		const dms *	d
	)			[inline]

Overloaded member function, provided for convenience.

It behaves essentially like the above function.

Parameters:

	r	Right Ascension
	d	Declination

Definition at line 95 of file skypoint.h.

void SkyPoint::set	(	const dms &	r,
		const dms &	d
	)

Sets RA, Dec and RA0, Dec0 according to arguments.

Does not set Altitude or Azimuth.

Parameters:

	r	Right Ascension
	d	Declination

Definition at line 29 of file skypoint.cpp.

void SkyPoint::setAlt

(

double

alt

)

[inline]

Overloaded member function, provided for convenience.

It behaves essentially like the above function.

Parameters:

alt

Altitude, expressed as a double.

Definition at line 157 of file skypoint.h.

void SkyPoint::setAlt

(

dms

alt

)

[inline]

Sets Alt, the Altitude.

Parameters:

alt

Altitude.

Definition at line 151 of file skypoint.h.

void SkyPoint::setAz

(

double

az

)

[inline]

Overloaded member function, provided for convenience.

It behaves essentially like the above function.

Parameters:

az

Azimuth, expressed as a double.

Definition at line 168 of file skypoint.h.

void SkyPoint::setAz

(

dms

az

)

[inline]

Sets Az, the Azimuth.

Parameters:

az

Azimuth.

Definition at line 162 of file skypoint.h.

void SkyPoint::setDec

(

double

d

)

[inline]

Overloaded member function, provided for convenience.

It behaves essentially like the above function.

Parameters:

d

Declination, expressed as a double.

Definition at line 146 of file skypoint.h.

void SkyPoint::setDec

(

dms

d

)

[inline]

Sets Dec, the current Declination.

Parameters:

d

Declination.

Definition at line 140 of file skypoint.h.

void SkyPoint::setDec0

(

double

d

)

[inline]

Overloaded member function, provided for convenience.

It behaves essentially like the above function.

Parameters:

d

Declination, expressed as a double.

Definition at line 124 of file skypoint.h.

void SkyPoint::setDec0

(

dms

d

)

[inline]

Sets Dec0, the catalog Declination.

Parameters:

d

catalog Declination.

Definition at line 118 of file skypoint.h.

void SkyPoint::setFromEcliptic	(	const dms *	Obliquity,
		const dms *	EcLong,
		const dms *	EcLat
	)

Set the current (RA, Dec) coordinates of the SkyPoint, given pointers to its Ecliptic (Long, Lat) coordinates, and to the current obliquity angle (the angle between the equator and ecliptic).

Definition at line 124 of file skypoint.cpp.

void SkyPoint::setRA

(

double

r

)

[inline]

Overloaded member function, provided for convenience.

It behaves essentially like the above function.

Parameters:

r

Right Ascension, expressed as a double.

Definition at line 135 of file skypoint.h.

void SkyPoint::setRA

(

dms

r

)

[inline]

Sets RA, the current Right Ascension.

Parameters:

r

Right Ascension.

Definition at line 129 of file skypoint.h.

void SkyPoint::setRA0

(

double

r

)

[inline]

Overloaded member function, provided for convenience.

It behaves essentially like the above function.

Parameters:

r

Right Ascension, expressed as a double.

Definition at line 113 of file skypoint.h.

void SkyPoint::setRA0

(

dms

r

)

[inline]

Sets RA0, the catalog Right Ascension.

Parameters:

r

catalog Right Ascension.

Definition at line 107 of file skypoint.h.

void SkyPoint::subtractEterms

(

void

)

Coordinates in the FK4 catalog include the effect of aberration due to the ellipticity of the orbit of the Earth.

Coordinates in the FK5 catalog do not include these terms. In order to convert from FK5 coordinates to B1950 (FK4) one has to use this function.

Definition at line 512 of file skypoint.cpp.

void SkyPoint::updateCoords	(	KSNumbers *	num,
		bool	includePlanets = true,
		const dms *	lat = 0,
		const dms *	LST = 0
	)			[virtual]

Determine the current coordinates (RA, Dec) from the catalog coordinates (RA0, Dec0), accounting for both precession and nutation.

Parameters:

	num	pointer to KSNumbers object containing current values of time-dependent variables.
	includePlanets	does nothing in this implementation (see KSPlanetBase::updateCoords()).
	lat	does nothing in this implementation (see KSPlanetBase::updateCoords()).
	LST	does nothing in this implementation (see KSPlanetBase::updateCoords()).

Reimplemented in KSPlanetBase, and StarObject.

Definition at line 235 of file skypoint.cpp.

double SkyPoint::vGeocentric	(	double	vhelio,
		long double	jd
	)

Computes the radial velocity of a source referred to the center of the earth from the radial velocity referred to the solar system barycenter.

Parameters:

	vhelio	radial velocity of the source referred to the barycenter of the solar system in km/s
	jd	Epoch expressed as julian day to which the source coordinates refer to.

Returns:

Radial velocity of the source referred to the center of the Earth in km/s

Definition at line 874 of file skypoint.cpp.

double SkyPoint::vGeoToVHelio	(	double	vgeo,
		long double	jd
	)

Computes the radial velocity of a source referred to the solar system barycenter from the velocity referred to the center of the earth.

Parameters:

	vgeo	radial velocity of the source referred to the center of the Earth [km/s]
	jd	Epoch expressed as julian day to which the source coordinates refer to.

Returns:

Radial velocity of the source referred to the solar system barycenter in km/s

Definition at line 879 of file skypoint.cpp.

double SkyPoint::vHeliocentric	(	double	vlsr,
		long double	jd
	)

Computes the radial velocity of a source referred to the solar system barycenter from the radial velocity referred to the Local Standard of Rest, aka known as VLSR.

To compute it we need the coordinates of the source the VLSR and the epoch for the source coordinates.

Parameters:

	vlsr	radial velocity of the source referred to the LSR in km/s
	jd	Epoch expressed as julian day to which the source coordinates refer to.

Returns:

Radial velocity of the source referred to the barycenter of the solar system in km/s

Definition at line 823 of file skypoint.cpp.

double SkyPoint::vHelioToVlsr	(	double	vhelio,
		long double	jd
	)

Computes the radial velocity of a source referred to the Local Standard of Rest, also known as VLSR from the radial velocity referred to the solar system barycenter.

Parameters:

	vhelio	radial velocity of the source referred to the LSR in km/s
	jd	Epoch expressed as julian day to which the source coordinates refer to.

Returns:

Radial velocity of the source referred to the barycenter of the solar system in km/s

Definition at line 828 of file skypoint.cpp.

double SkyPoint::vREarth

(

long double

jd0

)

Computes the velocity of any object projected on the direction of the source.

Parameters:

jd0

Julian day for which we compute the direction of the source

Returns:

velocity of the Earth projected on the direction of the source kms-1

Definition at line 833 of file skypoint.cpp.

double SkyPoint::vRSite

(

double

vsite[3]

)

Computes the velocity of any object (oberver's site) projected on the direction of the source.

Parameters:

vsite

velocity of that object in cartesian coordinates

Returns:

velocity of the object projected on the direction of the source kms-1

Definition at line 884 of file skypoint.cpp.

double SkyPoint::vRSun

(

long double

jd

)

Computes the velocity of the Sun projected on the direction of the source.

Parameters:

jd

Epoch expressed as julian day to which the source coordinates refer to.

Returns:

Radial velocity of the source referred to the barycenter of the solar system in km/s

Definition at line 783 of file skypoint.cpp.

double SkyPoint::vTopocentric	(	double	vgeo,
		double	vsite[3]
	)

Computes the radial velocity of a source referred to the observer site on the surface of the earth from the geocentric velovity and the velocity of the site referred to the center of the Earth.

Parameters:

	vgeo	radial velocity of the source referred to the center of the earth in km/s
	vsite	Velocity at which the observer moves referred to the center of the earth.

Returns:

Radial velocity of the source referred to the observer's site in km/s

Definition at line 900 of file skypoint.cpp.

double SkyPoint::vTopoToVGeo	(	double	vtopo,
		double	vsite[3]
	)

Computes the radial velocity of a source referred to the center of the Earth from the radial velocity referred to an observer site on the surface of the earth.

Parameters:

	vtopo	radial velocity of the source referred to the observer's site in km/s
	vsite	Velocity at which the observer moves referred to the center of the earth.

Returns:

Radial velocity of the source referred the center of the earth in km/s

Definition at line 895 of file skypoint.cpp.

---

The documentation for this class was generated from the following files:

• skypoint.h
• skypoint.cpp