astro::earth::refraction Namespace Reference

Namespaces
namespace	detail

Classes
struct	Params
	Atmospheric conditions for refraction calculations. More...

Enumerations
enum class	Model : uint8_t { BENNETT , SAEMUNDSSON }
	Atmospheric refraction model selector. More...

Functions
auto	bennett (const toolbox::AngleDeg &apparent_alt) -> toolbox::AngleDeg
	Bennett's formula for atmospheric refraction from apparent altitude.
auto	saemundsson (const toolbox::AngleDeg &true_alt) -> toolbox::AngleDeg
	Saemundsson's formula for atmospheric refraction from true (geometric) altitude.
auto	at_horizon (const Params &params={}) -> toolbox::AngleDeg
	Compute the refraction at the apparent horizon (apparent altitude = 0°).

Variables
constexpr double	NATIVE_TEMPERATURE_C
	Native temperature for the refraction models, in degrees Celsius.
constexpr double	NATIVE_PRESSURE_HPA
	Native pressure for the refraction models, in hectopascals.
constexpr double	NATIVE_TEMPERATURE_K
	The 283 K numerator in the T/P correction factor, derived from 10°C = 273 + 10 K.
constexpr double	SAEMUNDSSON_HORIZON_TOL_DEG
	Iteration tolerance for Saemundsson's horizon refraction, in degrees.
constexpr std::size_t	SAEMUNDSSON_HORIZON_MAX_ITER
	Maximum number of iterations for Saemundsson's horizon solve.

Enumeration Type Documentation

Model

enum class astro::earth::refraction::Model : uint8_t

strong

Atmospheric refraction model selector.

Enumerator
BENNETT
SAEMUNDSSON

Function Documentation

at_horizon()

auto astro::earth::refraction::at_horizon ( const Params & params = {} ) ->toolbox::AngleDeg

inlinenodiscard

Compute the refraction at the apparent horizon (apparent altitude = 0°).

Parameters

params

The atmospheric conditions. Defaults to 15°C/1013.25 hPa/Bennett.

Returns

The horizon refraction, positive in degrees.

Note

For Bennett the apparent altitude is already 0°, so the formula can be evaluated directly. For Saemundsson the input is the true altitude, which at the apparent horizon equals −R; this function iterates R = apply_tp_correction(saemundsson(−R), params) to convergence.

bennett()

auto astro::earth::refraction::bennett ( const toolbox::AngleDeg & apparent_alt ) ->toolbox::AngleDeg

inlinenodiscard

Bennett's formula for atmospheric refraction from apparent altitude.

Parameters

apparent_alt

The apparent altitude of the body (what an observer sees), in degrees.

Returns

The refraction angle in degrees (the formula yields a negligible negative value at exactly 90°).

Note

Meeus (16.3) gives the result in arcminutes for 10°C/1010 hPa. The returned value is the native (10°C/1010 hPa) refraction; at_horizon(Params) computes the T/P-corrected horizon refraction. The formula is valid for apparent altitudes in [0°, 90°] and becomes numerically unstable below about −2°.

See also

Jean Meeus, "Astronomical Algorithms", Second Edition, Chapter 16, Formula (16.3).

saemundsson()

auto astro::earth::refraction::saemundsson ( const toolbox::AngleDeg & true_alt ) ->toolbox::AngleDeg

inlinenodiscard

Saemundsson's formula for atmospheric refraction from true (geometric) altitude.

Parameters

true_alt

The true geometric altitude of the body, in degrees.

Returns

The refraction angle in degrees (the formula yields a negligible negative value at exactly 90°).

Note

Meeus (16.4) gives the result in arcminutes for 10°C/1010 hPa. The returned value is the native (10°C/1010 hPa) refraction; at_horizon(Params) computes the T/P-corrected horizon refraction. The input is the geometric altitude (before refraction), opposite to Bennett. The formula is valid for true altitudes in [0°, 90°] and becomes numerically unstable below about −2°.

See also

Jean Meeus, "Astronomical Algorithms", Second Edition, Chapter 16, Formula (16.4).

Variable Documentation

NATIVE_PRESSURE_HPA

double astro::earth::refraction::NATIVE_PRESSURE_HPA

inlineconstexpr

Native pressure for the refraction models, in hectopascals.

Note

Both Bennett (Meeus 16.3) and Saemundsson (Meeus 16.4) are tabulated for 10°C/1010 hPa.

NATIVE_TEMPERATURE_C

double astro::earth::refraction::NATIVE_TEMPERATURE_C

inlineconstexpr

Native temperature for the refraction models, in degrees Celsius.

Note

Both Bennett (Meeus 16.3) and Saemundsson (Meeus 16.4) are tabulated for 10°C/1010 hPa.

NATIVE_TEMPERATURE_K

double astro::earth::refraction::NATIVE_TEMPERATURE_K

inlineconstexpr

The 283 K numerator in the T/P correction factor, derived from 10°C = 273 + 10 K.

Note

The correction scales refraction by (P/1010) * (283/(273+T_c)).

SAEMUNDSSON_HORIZON_MAX_ITER

std::size_t astro::earth::refraction::SAEMUNDSSON_HORIZON_MAX_ITER

inlineconstexpr

Maximum number of iterations for Saemundsson's horizon solve.

SAEMUNDSSON_HORIZON_TOL_DEG

double astro::earth::refraction::SAEMUNDSSON_HORIZON_TOL_DEG

inlineconstexpr

Iteration tolerance for Saemundsson's horizon refraction, in degrees.