Venus

Functions
double	ln_get_venus_sdiam (double JD)
	Calcaluate the semidiameter of Venus in arc seconds.
int	ln_get_venus_rst (double JD, struct ln_lnlat_posn *observer, struct ln_rst_time *rst)
	Calculate the time of rise, set and transit for Venus.
void	ln_get_venus_helio_coords (double JD, struct ln_helio_posn *position)
	Calvulate Venus heliocentric coordinates.
void	ln_get_venus_equ_coords (double JD, struct ln_equ_posn *position)
	Calculate Venus equatorial coordinates.
double	ln_get_venus_earth_dist (double JD)
	Calculate the distance between Venus and the Earth.
double	ln_get_venus_solar_dist (double JD)
	Calculate the distance between Venus and the Sun.
double	ln_get_venus_magnitude (double JD)
	Calculate the visible magnitude of Venus.
double	ln_get_venus_disk (double JD)
	Calculate the illuminated fraction of Venus disk.
double	ln_get_venus_phase (double JD)
	Calculate the phase angle of Venus.
void	ln_get_venus_rect_helio (double JD, struct ln_rect_posn *position)
	Calculate Venus rectangular heliocentric coordinates.

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Detailed Description

Functions relating to the planet Venus.

All angles are expressed in degrees.

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Function Documentation

double ln_get_venus_disk

(

double

JD

)

Calculate the illuminated fraction of Venus disk.

Returns:

Illuminated fraction of Venus disk

Parameters:

JD

Julian day

Returns:

Illuminated fraction of venus disk

Calculate the illuminated fraction of Venus's disk for the given Julian day

References ln_get_earth_solar_dist(), ln_get_venus_earth_dist(), ln_get_venus_solar_dist(), and ln_helio_posn::R.

double ln_get_venus_earth_dist

(

double

JD

)

Calculate the distance between Venus and the Earth.

Calculate the distance between Venus and the Earth in AU.

Returns:

Distance in AU

Parameters:

JD

Julian day

Returns:

Distance in AU

Calculates the distance in AU between the Earth and Venus for the given julian day.

References ln_get_earth_helio_coords(), ln_get_rect_from_helio(), ln_get_venus_helio_coords(), ln_rect_posn::X, ln_rect_posn::Y, and ln_rect_posn::Z.

Referenced by ln_get_venus_disk(), ln_get_venus_magnitude(), ln_get_venus_phase(), and ln_get_venus_sdiam().

void ln_get_venus_equ_coords	(	double	JD,
		struct ln_equ_posn *	position
	)

Calculate Venus equatorial coordinates.

Parameters:

	JD	Julian Day
	position	Pointer to store position

Calculates Venus's equatorial position for given julian day. This function includes calculations for planetary aberration and refers to the FK5 reference frame.

To get the complete equatorial coordinates, corrections for nutation have to be applied.

The position returned is accurate to within 0.1 arcsecs..

References ln_equ_posn::dec, ln_get_rect_from_helio(), ln_get_solar_geom_coords(), ln_get_venus_helio_coords(), ln_rad_to_deg(), ln_range_degrees(), ln_equ_posn::ra, ln_rect_posn::X, ln_rect_posn::Y, and ln_rect_posn::Z.

Referenced by ln_get_venus_rst().

void ln_get_venus_helio_coords	(	double	JD,
		struct ln_helio_posn *	position
	)

Calvulate Venus heliocentric coordinates.

Parameters:

	JD	Julian Day
	position	Pointer to store new heliocentric position

Calculate Venus heliocentric (refered to the centre of the Sun) coordinates in the FK5 reference frame for the given julian day. Longitude and Latitude are in degrees, whilst radius vector is in AU.

References ln_helio_posn::B, ln_helio_posn::L, ln_rad_to_deg(), ln_range_degrees(), ln_vsop87_to_fk5(), and ln_helio_posn::R.

Referenced by ln_get_venus_earth_dist(), ln_get_venus_equ_coords(), ln_get_venus_rect_helio(), and ln_get_venus_solar_dist().

double ln_get_venus_magnitude

(

double

JD

)

Calculate the visible magnitude of Venus.

Returns:

Visible magnitude of Venus

Parameters:

JD

Julian day

Returns:

Visible magnitude of venus

Calculate the visible magnitude of Venus for the given julian day.

References ln_get_venus_earth_dist(), ln_get_venus_phase(), and ln_get_venus_solar_dist().

double ln_get_venus_phase

(

double

JD

)

Calculate the phase angle of Venus.

Calculate the phase angle of Venus (Sun - Venus - Earth).

Returns:

Phase angle of Venus (degrees)

Parameters:

JD

Julian day

Returns:

Phase angle of Venus (degrees)

Calculates the phase angle of Venus, that is, the angle Sun - Venus - Earth for the given Julian day.

References ln_get_earth_solar_dist(), ln_get_venus_earth_dist(), ln_get_venus_solar_dist(), ln_rad_to_deg(), and ln_helio_posn::R.

Referenced by ln_get_venus_magnitude().

void ln_get_venus_rect_helio	(	double	JD,
		struct ln_rect_posn *	position
	)

Calculate Venus rectangular heliocentric coordinates.

Parameters:

	JD	Julian day.
	position	ointer to return position

Calculate Venus rectangular heliocentric coordinates for the given Julian day. Coordinates are in AU.

References ln_get_rect_from_helio(), and ln_get_venus_helio_coords().

double ln_get_venus_rst	(	double	JD,
		struct ln_lnlat_posn *	observer,
		struct ln_rst_time *	rst
	)

Calculate the time of rise, set and transit for Venus.

Parameters:

	JD	Julian day
	observer	Observers position
	rst	Pointer to store Rise, Set and Transit time in JD

Returns:

0 for success, else 1 for circumpolar.

Calculate the time the rise, set and transit (crosses the local meridian at upper culmination) time of Venus for the given Julian day.

Note: this functions returns 1 if Venus is circumpolar, that is it remains the whole day either above or below the horizon.

References ln_get_body_rst_horizon(), and ln_get_venus_equ_coords().

double ln_get_venus_sdiam

(

double

JD

)

Calcaluate the semidiameter of Venus in arc seconds.

Parameters:

JD

Julian day

Returns:

Semidiameter in arc seconds

Calculate the semidiameter of Venus in arc seconds for the given julian day.

References ln_get_venus_earth_dist().

double ln_get_venus_solar_dist

(

double

JD

)

Calculate the distance between Venus and the Sun.

Calculate the distance between Venus and the Sun in AU.

Returns:

Distance in AU

Parameters:

JD

Julian day

Returns:

Distance in AU

Calculates the distance in AU between the Sun and Venus for the given julian day.

References ln_get_venus_helio_coords(), and ln_helio_posn::R.

Referenced by ln_get_venus_disk(), ln_get_venus_magnitude(), and ln_get_venus_phase().