com.mhuss.AstroLib

Class RiseSet

java.lang.Object

com.mhuss.AstroLib.RiseSet

public class RiseSet
extends java.lang.Object

Calculates rise & set times of the sun or moon, and also calculates twilight times (civil/nautical/astronomical).

Based on code by Bill Gray (www.projectpluto.com)

[Bill Gray's Comments:]
This class computes the times at which the sun or moon will rise and set during a given day starting on the given Julian day. It does this by computing the altitude of the object during each of the 24 hours of that day (and 1 hour of the next). What we really want to know is the object's altitude relative to the "rise/set altitude." This is the altitude at which the top of the object becomes visible, after correcting for refraction and (in the case of the Moon) topocentric parallax.

For the sun, this altitude is -.8333 degrees (its apparent radius is about .25 degrees, and refraction 'lifts it up' by .58333 degrees.) For the moon, this altitude is +.125 degrees.

If we find that the object was below this altitude at one hour, and above it on the next hour, then it must have risen in that interval; Conversely, if we find that the object was above this altitude at one hour, and below it on the next hour, then it must have set in that interval.

We then do an iterative search to find the instant during that hour that it rose or set. This starts with a guessed rise/set time in the middle of the particular hour in question. At each step, we look at the altitude of that object at that time, and use it to adjust the rise/set time based on the assumption that the motion was linear during the hour (this isn't a perfect assumption, but we still usually converge in a few iterations.)

As a side benefit, this function will also calculate twilight times by using the sun and just changing the event altitude. The modified altitudes are -6 degrees (civil twilight), -12 degrees (nautical twilight) and -18 degrees (astronomical twilight).

TimePair.a stores the rise (or twilight start) times.
TimePair.b stores the set (or twilight end) times.

Field Summary

Fields

Modifier and Type	Field and Description
static double	A_TWI_ALT Astronomical twilight altitude (when sun is 18 degrees below horizon).
static int	ASTRONOMICAL_TWI Calulation type (pseudo-enum)
static double	C_TWI_ALT Civil twilight altitude (when sun is 6 degrees below horizon).
static int	CIVIL_TWI Calulation type (pseudo-enum)
static int	CULMINATING State enum
static int	MOON Calulation type (pseudo-enum)
static double	MOON_ALT Lunar altitude adjustment
static double	N_TWI_ALT Nautical twilight altitude (when sun is 12 degrees below horizon).
static int	NAUTICAL_TWI Calulation type (pseudo-enum)
static double	PLANET_ALT Stellar altitude adjustment
static int	RISING State enum
static int	SETTING State enum
static int	SUN Calulation type (pseudo-enum)
static double	SUN_ALT Solar altitude adjustment
static double	SUN_TOPO_ALT Solar an lunar topocentric altitude adjustment
static int	UNKNOWN State enum

Constructor Summary

Constructors

Constructor and Description
RiseSet()

Method Summary

Modifier and Type	Method and Description
static TimePair	getTimes(int rsType, double jd, ObsInfo oi) Calculate the rise/set (or start/end) times.
static TimePair	getTimes(int rsType, double jd, ObsInfo oi, PlanetData pd) Calculate the rise/set (or start/end) times.

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

SUN

public static final int SUN

Calulation type (pseudo-enum)

See Also:

Constant Field Values

MOON

public static final int MOON

Calulation type (pseudo-enum)

See Also:

Constant Field Values

CIVIL_TWI

public static final int CIVIL_TWI

Calulation type (pseudo-enum)

See Also:

Constant Field Values

NAUTICAL_TWI

public static final int NAUTICAL_TWI

Calulation type (pseudo-enum)

See Also:

Constant Field Values

ASTRONOMICAL_TWI

public static final int ASTRONOMICAL_TWI

Calulation type (pseudo-enum)

See Also:

Constant Field Values

SUN_ALT

public static final double SUN_ALT

Solar altitude adjustment

SUN_TOPO_ALT

public static final double SUN_TOPO_ALT

Solar an lunar topocentric altitude adjustment

MOON_ALT

public static final double MOON_ALT

Lunar altitude adjustment

PLANET_ALT

public static final double PLANET_ALT

Stellar altitude adjustment

C_TWI_ALT

public static final double C_TWI_ALT

Civil twilight altitude (when sun is 6 degrees below horizon).

N_TWI_ALT

public static final double N_TWI_ALT

Nautical twilight altitude (when sun is 12 degrees below horizon).

A_TWI_ALT

public static final double A_TWI_ALT

Astronomical twilight altitude (when sun is 18 degrees below horizon).

UNKNOWN

public static final int UNKNOWN

State enum

See Also:

Constant Field Values

RISING

public static final int RISING

State enum

See Also:

Constant Field Values

SETTING

public static final int SETTING

State enum

See Also:

Constant Field Values

CULMINATING

public static final int CULMINATING

State enum

See Also:

Constant Field Values

Constructor Detail

RiseSet

public RiseSet()

Method Detail

getTimes

public static TimePair getTimes(int rsType,
                                double jd,
                                ObsInfo oi,
                                PlanetData pd)

Calculate the rise/set (or start/end) times.

Parameters:

rsType - Rise/Set type (SUN, MOON, CIVIL_TWI, NAUTICAL_TWI, or ASTRONOMICAL_TWI).

jd - The Julian day for which to calculate the desired information (set to 0h local time

oi - The observer's location

pd - A PlanetData instance to use for our calculations.

Returns:

the TimePair result, local time

getTimes

public static TimePair getTimes(int rsType,
                                double jd,
                                ObsInfo oi)

Calculate the rise/set (or start/end) times.

Parameters:

rsType - Rise/Set type (SUN, MOON, CIVIL_TWI, NAUTICAL_TWI, or ASTRONOMICAL_TWI).

jd - The Julian day for which to calculate the desired information

oi - The observer's location