| /* |
| ******************************************************************************* |
| * Copyright (C) 1996-2000, International Business Machines Corporation and * |
| * others. All Rights Reserved. * |
| ******************************************************************************* |
| * |
| * $Source: /xsrl/Nsvn/icu/icu4j/src/com/ibm/util/Attic/CalendarAstronomer.java,v $ |
| * $Date: 2000/11/28 22:17:06 $ |
| * $Revision: 1.5 $ |
| * |
| ***************************************************************************************** |
| */ |
| package com.ibm.util; |
| |
| import java.util.*; |
| import java.text.*; |
| |
| /** |
| * <code>CalendarAstronomer</code> is a class that can perform the calculations to |
| * determine the positions of the sun and moon, the time of sunrise and |
| * sunset, and other astronomy-related data. The calculations it performs |
| * are in some cases quite complicated, and this utility class saves you |
| * the trouble of worrying about them. |
| * <p> |
| * The measurement of time is a very important part of astronomy. Because |
| * astronomical bodies are constantly in motion, observations are only valid |
| * at a given moment in time. Accordingly, each <code>CalendarAstronomer</code> |
| * object has a <code>time</code> property that determines the date |
| * and time for which its calculations are performed. You can set and |
| * retrieve this property with {@link #setDate setDate}, {@link #getDate getDate} |
| * and related methods. |
| * <p> |
| * Almost all of the calculations performed by this class, or by any |
| * astronomer, are approximations to various degrees of accuracy. The |
| * calculations in this class are mostly modelled after those described |
| * in the book |
| * <a href="http://www.amazon.com/exec/obidos/ISBN=0521356997" target="_top"> |
| * Practical Astronomy With Your Calculator</a>, by Peter J. |
| * Duffett-Smith, Cambridge University Press, 1990. This is an excellent |
| * book, and if you want a greater understanding of how these calculations |
| * are performed it a very good, readable starting point. |
| * <p> |
| * <strong>WARNING:</strong> This class is very early in its development, and |
| * it is highly likely that its API will change to some degree in the future. |
| * At the moment, it basically does just enough to support {@link IslamicCalendar} |
| * and {@link ChineseCalendar}. |
| * |
| * @author Laura Werner |
| * @author Alan Liu |
| */ |
| public class CalendarAstronomer { |
| |
| //------------------------------------------------------------------------- |
| // Astronomical constants |
| //------------------------------------------------------------------------- |
| |
| /** |
| * The number of standard hours in one sidereal day. |
| * Approximately 24.93. |
| */ |
| public static final double SIDEREAL_DAY = 23.93446960027; |
| |
| /** |
| * The number of sidereal hours in one mean solar day. |
| * Approximately 24.07. |
| */ |
| public static final double SOLAR_DAY = 24.065709816; |
| |
| /** |
| * The average number of solar days from one new moon to the next. This is the time |
| * it takes for the moon to return the same ecliptic longitude as the sun. |
| * It is longer than the sidereal month because the sun's longitude increases |
| * during the year due to the revolution of the earth around the sun. |
| * Approximately 29.53. |
| * |
| * @see #SIDEREAL_MONTH |
| */ |
| public static final double SYNODIC_MONTH = 29.530588853; |
| |
| /** |
| * The average number of days it takes |
| * for the moon to return to the same ecliptic longitude relative to the |
| * stellar background. This is referred to as the sidereal month. |
| * It is shorter than the synodic month due to |
| * the revolution of the earth around the sun. |
| * Approximately 27.32. |
| * |
| * @see #SYNODIC_MONTH |
| */ |
| public static final double SIDEREAL_MONTH = 27.32166; |
| |
| /** |
| * The average number number of days between successive vernal equinoxes. |
| * Due to the precession of the earth's |
| * axis, this is not precisely the same as the sidereal year. |
| * Approximately 365.24 |
| * |
| * @see #SIDEREAL_YEAR |
| */ |
| public static final double TROPICAL_YEAR = 365.242191; |
| |
| /** |
| * The average number of days it takes |
| * for the sun to return to the same position against the fixed stellar |
| * background. This is the duration of one orbit of the earth about the sun |
| * as it would appear to an outside observer. |
| * Due to the precession of the earth's |
| * axis, this is not precisely the same as the tropical year. |
| * Approximately 365.25. |
| * |
| * @see #TROPICAL_YEAR |
| */ |
| public static final double SIDEREAL_YEAR = 365.25636; |
| |
| //------------------------------------------------------------------------- |
| // Time-related constants |
| //------------------------------------------------------------------------- |
| |
| /** The number of milliseconds in one second. */ |
| public static final int SECOND_MS = 1000; |
| |
| /** The number of milliseconds in one minute. */ |
| public static final int MINUTE_MS = 60*SECOND_MS; |
| |
| /** The number of milliseconds in one hour. */ |
| public static final int HOUR_MS = 60*MINUTE_MS; |
| |
| /** The number of milliseconds in one day. */ |
| public static final long DAY_MS = 24*HOUR_MS; |
| |
| /** |
| * The start of the julian day numbering scheme used by astronomers, which |
| * is 1/1/4713 BC (Julian), 12:00 GMT. This is given as the number of milliseconds |
| * since 1/1/1970 AD (Gregorian), a negative number. |
| * Note that julian day numbers and |
| * the Julian calendar are <em>not</em> the same thing. Also note that |
| * julian days start at <em>noon</em>, not midnight. |
| */ |
| public static final long JULIAN_EPOCH_MS = -210866760000000L; |
| |
| |
| //------------------------------------------------------------------------- |
| // Assorted private data used for conversions |
| //------------------------------------------------------------------------- |
| |
| // My own copies of these so compilers are more likely to optimize them away |
| static private final double PI = 3.14159265358979323846; |
| static private final double PI2 = PI * 2.0; |
| |
| static private final double HOUR_RAD = PI / 12; // hours -> radians |
| static private final double RAD_HOUR = 12 / PI; // radians -> hours |
| static private final double DEG_RAD = PI / 180; // degrees -> radians |
| static private final double RAD_DEG = 180 / PI; // radians -> degrees |
| |
| //------------------------------------------------------------------------- |
| // Constructors |
| //------------------------------------------------------------------------- |
| |
| /** |
| * Construct a new <code>CalendarAstronomer</code> object that is initialized to |
| * the current date and time. |
| */ |
| public CalendarAstronomer() { |
| this(System.currentTimeMillis()); |
| } |
| |
| /** |
| * Construct a new <code>CalendarAstronomer</code> object that is initialized to |
| * the specified date and time. |
| */ |
| public CalendarAstronomer(Date d) { |
| this(d.getTime()); |
| } |
| |
| /** |
| * Construct a new <code>CalendarAstronomer</code> object that is initialized to |
| * the specified time. The time is expressed as a number of milliseconds since |
| * January 1, 1970 AD (Gregorian). |
| * |
| * @see java.util.Date#getTime |
| */ |
| public CalendarAstronomer(long aTime) { |
| time = aTime; |
| } |
| |
| /** |
| * Construct a new <code>CalendarAstronomer</code> object with the given |
| * latitude and longitude. The object's time is set to the current |
| * date and time. |
| * <p> |
| * @param longitude The desired longitude, in <em>degrees</em> east of |
| * the Greenwich meridian. |
| * |
| * @param latitude The desired latitude, in <em>degrees</em>. Positive |
| * values signify North, negative South. |
| * |
| * @see java.util.Date#getTime |
| */ |
| public CalendarAstronomer(double longitude, double latitude) { |
| this(); |
| fLongitude = normPI(longitude * DEG_RAD); |
| fLatitude = normPI(latitude * DEG_RAD); |
| fGmtOffset = (long)(fLongitude * 24 * HOUR_MS / PI2); |
| } |
| |
| |
| //------------------------------------------------------------------------- |
| // Time and date getters and setters |
| //------------------------------------------------------------------------- |
| |
| /** |
| * Set the current date and time of this <code>CalendarAstronomer</code> object. All |
| * astronomical calculations are performed based on this time setting. |
| * |
| * @param aTime the date and time, expressed as the number of milliseconds since |
| * 1/1/1970 0:00 GMT (Gregorian). |
| * |
| * @see #setDate |
| * @see #getTime |
| */ |
| public void setTime(long aTime) { |
| time = aTime; |
| clearCache(); |
| } |
| |
| /** |
| * Set the current date and time of this <code>CalendarAstronomer</code> object. All |
| * astronomical calculations are performed based on this time setting. |
| * |
| * @param aTime the time and date, expressed as a <code>Date</code> object. |
| * |
| * @see #setTime |
| * @see #getDate |
| */ |
| public void setDate(Date date) { |
| setTime(date.getTime()); |
| } |
| |
| /** |
| * Set the current date and time of this <code>CalendarAstronomer</code> object. All |
| * astronomical calculations are performed based on this time setting. |
| * |
| * @param jdn the desired time, expressed as a "julian day number", |
| * which is the number of elapsed days since |
| * 1/1/4713 BC (Julian), 12:00 GMT. Note that julian day |
| * numbers start at <em>noon</em>. To get the jdn for |
| * the corresponding midnight, subtract 0.5. |
| * |
| * @see #getJulianDay |
| * @see #JULIAN_EPOCH_MS |
| */ |
| public void setJulianDay(double jdn) { |
| time = (long)(jdn * DAY_MS) + JULIAN_EPOCH_MS; |
| clearCache(); |
| julianDay = jdn; |
| } |
| |
| /** |
| * Get the current time of this <code>CalendarAstronomer</code> object, |
| * represented as the number of milliseconds since |
| * 1/1/1970 AD 0:00 GMT (Gregorian). |
| * |
| * @see #setTime |
| * @see #getDate |
| */ |
| public long getTime() { |
| return time; |
| } |
| |
| /** |
| * Get the current time of this <code>CalendarAstronomer</code> object, |
| * represented as a <code>Date</code> object. |
| * |
| * @see #setDate |
| * @see #getTime |
| */ |
| public Date getDate() { |
| return new Date(time); |
| } |
| |
| /** |
| * Get the current time of this <code>CalendarAstronomer</code> object, |
| * expressed as a "julian day number", which is the number of elapsed |
| * days since 1/1/4713 BC (Julian), 12:00 GMT. |
| * |
| * @see #setJulianDay |
| * @see #JULIAN_EPOCH_MS |
| */ |
| public double getJulianDay() { |
| if (julianDay == INVALID) { |
| julianDay = (double)(time - JULIAN_EPOCH_MS) / (double)DAY_MS; |
| } |
| return julianDay; |
| } |
| |
| /** |
| * Return this object's time expressed in julian centuries: |
| * the number of centuries after 1/1/1900 AD, 12:00 GMT |
| * |
| * @see #getJulianDay |
| */ |
| public double getJulianCentury() { |
| if (julianCentury == INVALID) { |
| julianCentury = (getJulianDay() - 2415020.0) / 36525; |
| } |
| return julianCentury; |
| } |
| |
| /** |
| * Returns the current Greenwich sidereal time, measured in hours |
| */ |
| public double getGreenwichSidereal() { |
| if (siderealTime == INVALID) { |
| // See page 86 of "Practial Astronomy with your Calculator", |
| // by Peter Duffet-Smith, for details on the algorithm. |
| |
| double UT = normalize((double)time/HOUR_MS, 24); |
| |
| siderealTime = normalize(getSiderealOffset() + UT*1.002737909, 24); |
| } |
| return siderealTime; |
| } |
| |
| private double getSiderealOffset() { |
| if (siderealT0 == INVALID) { |
| double JD = Math.floor(getJulianDay() - 0.5) + 0.5; |
| double S = JD - 2451545.0; |
| double T = S / 36525.0; |
| siderealT0 = normalize(6.697374558 + 2400.051336*T + 0.000025862*T*T, 24); |
| } |
| return siderealT0; |
| } |
| |
| /** |
| * Returns the current local sidereal time, measured in hours |
| */ |
| public double getLocalSidereal() { |
| return normalize(getGreenwichSidereal() + (double)fGmtOffset/HOUR_MS, 24); |
| } |
| |
| /** |
| * Converts local sidereal time to Universal Time. |
| * |
| * @param lst The Local Sidereal Time, in hours since sidereal midnight |
| * on this object's current date. |
| * |
| * @return The corresponding Universal Time, in milliseconds since |
| * 1 Jan 1970, GMT. |
| */ |
| private long lstToUT(double lst) { |
| // Convert to local mean time |
| double lt = normalize((lst - getSiderealOffset()) * 0.9972695663, 24); |
| |
| // Then find local midnight on this day |
| long base = DAY_MS * ((time + fGmtOffset)/DAY_MS) - fGmtOffset; |
| |
| //out(" lt =" + lt + " hours"); |
| //out(" base=" + new Date(base)); |
| |
| return base + (long)(lt * HOUR_MS); |
| } |
| |
| |
| //------------------------------------------------------------------------- |
| // Coordinate transformations, all based on the current time of this object |
| //------------------------------------------------------------------------- |
| |
| /** |
| * Convert from ecliptic to equatorial coordinates. |
| * |
| * @param ecliptic A point in the sky in ecliptic coordinates. |
| * @return The corresponding point in equatorial coordinates. |
| */ |
| public final Equatorial eclipticToEquatorial(Ecliptic ecliptic) |
| { |
| return eclipticToEquatorial(ecliptic.longitude, ecliptic.latitude); |
| } |
| |
| /** |
| * Convert from ecliptic to equatorial coordinates. |
| * |
| * @param eclipLong The ecliptic longitude |
| * @param eclipLat The ecliptic latitude |
| * |
| * @return The corresponding point in equatorial coordinates. |
| */ |
| public final Equatorial eclipticToEquatorial(double eclipLong, double eclipLat) |
| { |
| // See page 42 of "Practial Astronomy with your Calculator", |
| // by Peter Duffet-Smith, for details on the algorithm. |
| |
| double obliq = eclipticObliquity(); |
| double sinE = Math.sin(obliq); |
| double cosE = Math.cos(obliq); |
| |
| double sinL = Math.sin(eclipLong); |
| double cosL = Math.cos(eclipLong); |
| |
| double sinB = Math.sin(eclipLat); |
| double cosB = Math.cos(eclipLat); |
| double tanB = Math.tan(eclipLat); |
| |
| return new Equatorial(Math.atan2(sinL*cosE - tanB*sinE, cosL), |
| Math.asin(sinB*cosE + cosB*sinE*sinL) ); |
| } |
| |
| /** |
| * Convert from ecliptic longitude to equatorial coordinates. |
| * |
| * @param eclipLong The ecliptic longitude |
| * |
| * @return The corresponding point in equatorial coordinates. |
| */ |
| public final Equatorial eclipticToEquatorial(double eclipLong) |
| { |
| return eclipticToEquatorial(eclipLong, 0); // TODO: optimize |
| } |
| |
| |
| public Horizon eclipticToHorizon(double eclipLong) |
| { |
| Equatorial equatorial = eclipticToEquatorial(eclipLong); |
| |
| double H = getLocalSidereal()*PI/12 - equatorial.ascension; // Hour-angle |
| |
| double sinH = Math.sin(H); |
| double cosH = Math.cos(H); |
| double sinD = Math.sin(equatorial.declination); |
| double cosD = Math.cos(equatorial.declination); |
| double sinL = Math.sin(fLatitude); |
| double cosL = Math.cos(fLatitude); |
| |
| double altitude = Math.asin(sinD*sinL + cosD*cosL*cosH); |
| double azimuth = Math.atan2(-cosD*cosL*sinH, sinD - sinL * Math.sin(altitude)); |
| |
| return new Horizon(azimuth, altitude); |
| } |
| |
| |
| //------------------------------------------------------------------------- |
| // The Sun |
| //------------------------------------------------------------------------- |
| |
| // |
| // Parameters of the Sun's orbit as of 1/1/1990 |
| // Angles are in radians (after multiplying by PI/180) |
| // |
| double jdnEpoch = 2447891.5; // JDN of epoch (Jan 0.0 1990) |
| |
| double sunEtaG = 279.403303 * PI/180; // Ecliptic longitude at epoch |
| double sunOmegaG = 282.768422 * PI/180; // Ecliptic longitude of perigee |
| double sunE = 0.016713; // Eccentricity of orbit |
| double sunR0 = 1.495585e8; // Semi-major axis in KM |
| double sunTheta0 = 0.533128 * PI/180; // Angular diameter at R0 |
| |
| /** |
| * The longitude of the sun at the time specified by this object. |
| * The longitude is measured in radians along the ecliptic |
| * from the "first point of Aries," the point at which the ecliptic |
| * crosses the earth's equatorial plane at the vernal equinox. |
| * <p> |
| * Currently, this method uses an approximation of the two-body Kepler's |
| * equation for the earth and the sun. It does not take into account the |
| * perturbations caused by the other planets, the moon, etc. |
| */ |
| public double getSunLongitude() |
| { |
| // See page 86 of "Practial Astronomy with your Calculator", |
| // by Peter Duffet-Smith, for details on the algorithm. |
| |
| if (sunLongitude == INVALID) { |
| double day = getJulianDay() - jdnEpoch; // Days since epoch |
| |
| // Find the angular distance the sun in a fictitious |
| // circular orbit has travelled since the epoch. |
| double epochAngle = norm2PI(PI2/TROPICAL_YEAR*day); |
| |
| // The epoch wasn't at the sun's perigee; find the angular distance |
| // since perigee, which is called the "mean anomaly" |
| meanAnomalySun = norm2PI(epochAngle + sunEtaG - sunOmegaG); |
| |
| // Now find the "true anomaly", e.g. the real solar longitude |
| // by solving Kepler's equation for an elliptical orbit |
| sunLongitude = norm2PI(trueAnomaly(meanAnomalySun, sunE) + sunOmegaG); |
| } |
| return sunLongitude; |
| } |
| |
| /** |
| * The position of the sun at this object's current date and time, |
| * in equatorial coordinates. |
| */ |
| public Equatorial getSunPosition() { |
| return eclipticToEquatorial(getSunLongitude(), 0); |
| } |
| |
| private static class SolarLongitude { |
| double value; |
| SolarLongitude(double val) { value = val; } |
| } |
| |
| /** |
| * Constant representing the vernal equinox. |
| * For use with {@link #getSunTime getSunTime}. |
| * Note: In this case, "vernal" refers to the northern hemisphere's seasons. |
| */ |
| public static final SolarLongitude VERNAL_EQUINOX = new SolarLongitude(0); |
| |
| /** |
| * Constant representing the summer solstice. |
| * For use with {@link #getSunTime getSunTime}. |
| * Note: In this case, "summer" refers to the northern hemisphere's seasons. |
| */ |
| public static final SolarLongitude SUMMER_SOLSTICE = new SolarLongitude(PI/2); |
| |
| /** |
| * Constant representing the autumnal equinox. |
| * For use with {@link #getSunTime getSunTime}. |
| * Note: In this case, "autumn" refers to the northern hemisphere's seasons. |
| */ |
| public static final SolarLongitude AUTUMN_EQUINOX = new SolarLongitude(PI); |
| |
| /** |
| * Constant representing the winter solstice. |
| * For use with {@link #getSunTime getSunTime}. |
| * Note: In this case, "winter" refers to the northern hemisphere's seasons. |
| */ |
| public static final SolarLongitude WINTER_SOLSTICE = new SolarLongitude((PI*3)/2); |
| |
| /** |
| * Find the next time at which the sun's ecliptic longitude will have |
| * the desired value. |
| */ |
| public long getSunTime(double desired, boolean next) |
| { |
| return timeOfAngle( new AngleFunc() { public double eval() { return getSunLongitude(); } }, |
| desired, |
| TROPICAL_YEAR, |
| MINUTE_MS, |
| next); |
| } |
| |
| /** |
| * Find the next time at which the sun's ecliptic longitude will have |
| * the desired value. |
| */ |
| public long getSunTime(SolarLongitude desired, boolean next) { |
| return getSunTime(desired.value, next); |
| } |
| |
| /** |
| * Returns the time (GMT) of sunrise or sunset on the local date to which |
| * this calendar is currently set. |
| */ |
| public long getSunRiseSet(boolean rise) |
| { |
| // Make a rough guess: 6am or 6pm local time on the current day |
| long noon = ((time + fGmtOffset)/DAY_MS)*DAY_MS - fGmtOffset + 12*HOUR_MS; |
| |
| setTime(noon + (long)((rise ? -6 : 6) * HOUR_MS)); |
| |
| return riseOrSet(new CoordFunc() { |
| public Equatorial eval() { return getSunPosition(); } |
| }, |
| rise, |
| .533 * DEG_RAD, // Angular Diameter |
| 34 /60.0 * DEG_RAD, // Refraction correction |
| MINUTE_MS); // Desired accuracy |
| } |
| |
| //------------------------------------------------------------------------- |
| // The Moon |
| //------------------------------------------------------------------------- |
| |
| static final double moonL0 = 318.351648 * PI/180; // Mean long. at epoch |
| static final double moonP0 = 36.340410 * PI/180; // Mean long. of perigee |
| static final double moonN0 = 318.510107 * PI/180; // Mean long. of node |
| static final double moonI = 5.145366 * PI/180; // Inclination of orbit |
| static final double moonE = 0.054900; // Eccentricity of orbit |
| |
| // These aren't used right now |
| static final double moonA = 3.84401e5; // semi-major axis (km) |
| static final double moonT0 = 0.5181 * PI/180; // Angular size at distance A |
| static final double moonPi = 0.9507 * PI/180; // Parallax at distance A |
| |
| /** |
| * The position of the moon at the time set on this |
| * object, in equatorial coordinates. |
| */ |
| public Equatorial getMoonPosition() |
| { |
| // |
| // See page 142 of "Practial Astronomy with your Calculator", |
| // by Peter Duffet-Smith, for details on the algorithm. |
| // |
| if (moonPosition == null) { |
| // Calculate the solar longitude. Has the side effect of |
| // filling in "meanAnomalySun" as well. |
| double sunLongitude = getSunLongitude(); |
| |
| // |
| // Find the # of days since the epoch of our orbital parameters. |
| // TODO: Convert the time of day portion into ephemeris time |
| // |
| double day = getJulianDay() - jdnEpoch; // Days since epoch |
| |
| // Calculate the mean longitude and anomaly of the moon, based on |
| // a circular orbit. Similar to the corresponding solar calculation. |
| double meanLongitude = norm2PI(13.1763966*PI/180*day + moonL0); |
| double meanAnomalyMoon = norm2PI(meanLongitude - 0.1114041*PI/180 * day - moonP0); |
| |
| // |
| // Calculate the following corrections: |
| // Evection: the sun's gravity affects the moon's eccentricity |
| // Annual Eqn: variation in the effect due to earth-sun distance |
| // A3: correction factor (for ???) |
| // |
| double evection = 1.2739*PI/180 * Math.sin(2 * (meanLongitude - sunLongitude) |
| - meanAnomalyMoon); |
| double annual = 0.1858*PI/180 * Math.sin(meanAnomalySun); |
| double a3 = 0.3700*PI/180 * Math.sin(meanAnomalySun); |
| |
| meanAnomalyMoon += evection - annual - a3; |
| |
| // |
| // More correction factors: |
| // center equation of the center correction |
| // a4 yet another error correction (???) |
| // |
| // TODO: Skip the equation of the center correction and solve Kepler's eqn? |
| // |
| double center = 6.2886*PI/180 * Math.sin(meanAnomalyMoon); |
| double a4 = 0.2140*PI/180 * Math.sin(2 * meanAnomalyMoon); |
| |
| // Now find the moon's corrected longitude |
| moonLongitude = meanLongitude + evection + center - annual + a4; |
| |
| // |
| // And finally, find the variation, caused by the fact that the sun's |
| // gravitational pull on the moon varies depending on which side of |
| // the earth the moon is on |
| // |
| double variation = 0.6583*PI/180 * Math.sin(2*(moonLongitude - sunLongitude)); |
| |
| moonLongitude += variation; |
| |
| // |
| // What we've calculated so far is the moon's longitude in the plane |
| // of its own orbit. Now map to the ecliptic to get the latitude |
| // and longitude. First we need to find the longitude of the ascending |
| // node, the position on the ecliptic where it is crossed by the moon's |
| // orbit as it crosses from the southern to the northern hemisphere. |
| // |
| double nodeLongitude = norm2PI(moonN0 - 0.0529539*PI/180 * day); |
| |
| nodeLongitude -= 0.16*PI/180 * Math.sin(meanAnomalySun); |
| |
| double y = Math.sin(moonLongitude - nodeLongitude); |
| double x = Math.cos(moonLongitude - nodeLongitude); |
| |
| moonEclipLong = Math.atan2(y*Math.cos(moonI), x) + nodeLongitude; |
| double moonEclipLat = Math.asin(y * Math.sin(moonI)); |
| |
| moonPosition = eclipticToEquatorial(moonEclipLong, moonEclipLat); |
| } |
| return moonPosition; |
| } |
| |
| /** |
| * The "age" of the moon at the time specified in this object. |
| * This is really the angle between the |
| * current ecliptic longitudes of the sun and the moon, |
| * measured in radians. |
| * |
| * @see #getMoonPhase |
| */ |
| public double getMoonAge() { |
| // See page 147 of "Practial Astronomy with your Calculator", |
| // by Peter Duffet-Smith, for details on the algorithm. |
| // |
| // Force the moon's position to be calculated. We're going to use |
| // some the intermediate results cached during that calculation. |
| // |
| getMoonPosition(); |
| |
| return norm2PI(moonEclipLong - sunLongitude); |
| } |
| |
| /** |
| * Calculate the phase of the moon at the time set in this object. |
| * The returned phase is a <code>double</code> in the range |
| * <code>0 <= phase < 1</code>, interpreted as follows: |
| * <ul> |
| * <li>0.00: New moon |
| * <li>0.25: First quarter |
| * <li>0.50: Full moon |
| * <li>0.75: Last quarter |
| * </ul> |
| * |
| * @see #getMoonAge |
| */ |
| public double getMoonPhase() { |
| // See page 147 of "Practial Astronomy with your Calculator", |
| // by Peter Duffet-Smith, for details on the algorithm. |
| return 0.5 * (1 - Math.cos(getMoonAge())); |
| } |
| |
| private static class MoonAge { |
| double value; |
| MoonAge(double val) { value = val; } |
| } |
| |
| /** |
| * Constant representing a new moon. |
| * For use with {@link #getMoonTime getMoonTime} |
| */ |
| public static final MoonAge NEW_MOON = new MoonAge(0); |
| |
| /** |
| * Constant representing the moon's first quarter. |
| * For use with {@link #getMoonTime getMoonTime} |
| */ |
| public static final MoonAge FIRST_QUARTER = new MoonAge(PI/2); |
| |
| /** |
| * Constant representing a full moon. |
| * For use with {@link #getMoonTime getMoonTime} |
| */ |
| public static final MoonAge FULL_MOON = new MoonAge(PI); |
| |
| /** |
| * Constant representing the moon's last quarter. |
| * For use with {@link #getMoonTime getMoonTime} |
| */ |
| public static final MoonAge LAST_QUARTER = new MoonAge((PI*3)/2); |
| |
| /** |
| * Find the next or previous time at which the Moon's ecliptic |
| * longitude will have the desired value. |
| * <p> |
| * @param desired The desired longitude. |
| * @param next <tt>true</tt> if the next occurrance of the phase |
| * is desired, <tt>false</tt> for the previous occurrance. |
| */ |
| public long getMoonTime(double desired, boolean next) |
| { |
| return timeOfAngle( new AngleFunc() { |
| public double eval() { return getMoonAge(); } }, |
| desired, |
| SYNODIC_MONTH, |
| MINUTE_MS, |
| next); |
| } |
| |
| /** |
| * Find the next or previous time at which the moon will be in the |
| * desired phase. |
| * <p> |
| * @param desired The desired phase of the moon. |
| * @param next <tt>true</tt> if the next occurrance of the phase |
| * is desired, <tt>false</tt> for the previous occurrance. |
| */ |
| public long getMoonTime(MoonAge desired, boolean next) { |
| return getMoonTime(desired.value, next); |
| } |
| |
| /** |
| * Returns the time (GMT) of sunrise or sunset on the local date to which |
| * this calendar is currently set. |
| */ |
| public long getMoonRiseSet(boolean rise) |
| { |
| return riseOrSet(new CoordFunc() { |
| public Equatorial eval() { return getMoonPosition(); } |
| }, |
| rise, |
| .533 * DEG_RAD, // Angular Diameter |
| 34 /60.0 * DEG_RAD, // Refraction correction |
| MINUTE_MS); // Desired accuracy |
| } |
| |
| //------------------------------------------------------------------------- |
| // Interpolation methods for finding the time at which a given event occurs |
| //------------------------------------------------------------------------- |
| |
| private interface AngleFunc { |
| public double eval(); |
| }; |
| |
| private long timeOfAngle(AngleFunc func, double desired, |
| double periodDays, long epsilon, boolean next) |
| { |
| // Find the value of the function at the current time |
| double lastAngle = func.eval(); |
| |
| // Find out how far we are from the desired angle |
| double deltaAngle = norm2PI(desired - lastAngle) ; |
| |
| // Using the average period, estimate the next (or previous) time at |
| // which the desired angle occurs. |
| double deltaT = (deltaAngle + (next ? 0 : -PI2)) * (periodDays*DAY_MS) / PI2; |
| |
| double lastDeltaT = deltaT; // Liu |
| long startTime = time; // Liu |
| |
| setTime(time + (long)deltaT); |
| |
| // Now iterate until we get the error below epsilon. Throughout |
| // this loop we use normPI to get values in the range -Pi to Pi, |
| // since we're using them as correction factors rather than absolute angles. |
| do { |
| // Evaluate the function at the time we've estimated |
| double angle = func.eval(); |
| |
| // Find the # of milliseconds per radian at this point on the curve |
| double factor = Math.abs(deltaT / normPI(angle-lastAngle)); |
| |
| // Correct the time estimate based on how far off the angle is |
| deltaT = normPI(desired - angle) * factor; |
| |
| // HACK: |
| // |
| // If abs(deltaT) begins to diverge we need to quit this loop. |
| // This only appears to happen when attempting to locate, for |
| // example, a new moon on the day of the new moon. E.g.: |
| // |
| // This result is correct: |
| // newMoon(7508(Mon Jul 23 00:00:00 CST 1990,false))= |
| // Sun Jul 22 10:57:41 CST 1990 |
| // |
| // But attempting to make the same call a day earlier causes deltaT |
| // to diverge: |
| // CalendarAstronomer.timeOfAngle() diverging: 1.348508727575625E9 -> |
| // 1.3649828540224032E9 |
| // newMoon(7507(Sun Jul 22 00:00:00 CST 1990,false))= |
| // Sun Jul 08 13:56:15 CST 1990 |
| // |
| // As a temporary solution, we catch this specific condition and |
| // adjust our start time by one eighth period days (either forward |
| // or backward) and try again. |
| // Liu 11/9/00 |
| if (Math.abs(deltaT) > Math.abs(lastDeltaT)) { |
| long delta = (long) (periodDays * DAY_MS / 8); |
| setTime(startTime + (next ? delta : -delta)); |
| return timeOfAngle(func, desired, periodDays, epsilon, next); |
| } |
| |
| lastDeltaT = deltaT; |
| lastAngle = angle; |
| |
| setTime(time + (long)deltaT); |
| } |
| while (Math.abs(deltaT) > epsilon); |
| |
| return time; |
| } |
| |
| private interface CoordFunc { |
| public Equatorial eval(); |
| }; |
| |
| private long riseOrSet(CoordFunc func, boolean rise, |
| double diameter, double refraction, |
| long epsilon) |
| { |
| Equatorial pos = null; |
| double tanL = Math.tan(fLatitude); |
| long deltaT = Long.MAX_VALUE; |
| int count = 0; |
| |
| // |
| // Calculate the object's position at the current time, then use that |
| // position to calculate the time of rising or setting. The position |
| // will be different at that time, so iterate until the error is allowable. |
| // |
| do { |
| // See "Practical Astronomy With Your Calculator, section 33. |
| pos = func.eval(); |
| double angle = Math.acos(-tanL * Math.tan(pos.declination)); |
| double lst = ((rise ? PI2-angle : angle) + pos.ascension ) * 24 / PI2; |
| |
| // Convert from LST to Universal Time. |
| long newTime = lstToUT( lst ); |
| |
| deltaT = newTime - time; |
| setTime(newTime); |
| } |
| while (++ count < 5 && Math.abs(deltaT) > epsilon); |
| |
| // Calculate the correction due to refraction and the object's angular diameter |
| double cosD = Math.cos(pos.declination); |
| double psi = Math.acos(Math.sin(fLatitude) / cosD); |
| double x = diameter / 2 + refraction; |
| double y = Math.asin(Math.sin(x) / Math.sin(psi)); |
| long delta = (long)((240 * y * RAD_DEG / cosD)*SECOND_MS); |
| |
| return time + (rise ? -delta : delta); |
| } |
| |
| //------------------------------------------------------------------------- |
| // Other utility methods |
| //------------------------------------------------------------------------- |
| |
| private static final double normalize(double value, double range) { |
| return value - range * Math.floor(value / range); |
| } |
| |
| /** |
| * Normalize an angle so that it's in the range 0 - 2pi. |
| * For positive angles this is just (angle % 2pi), but the Java |
| * mod operator doesn't work that way for negative numbers.... |
| */ |
| private static final double norm2PI(double angle) { |
| return normalize(angle, PI2); |
| } |
| |
| /** |
| * Normalize an angle into the range -PI - PI |
| */ |
| private static final double normPI(double angle) { |
| return normalize(angle + PI, PI2) - PI; |
| } |
| |
| /** |
| * Find the "true anomaly" (longitude) of an object from |
| * its mean anomaly and the eccentricity of its orbit. This uses |
| * an iterative solution to Kepler's equation. |
| * |
| * @param meanAnomaly The object's longitude calculated as if it were in |
| * a regular, circular orbit, measured in radians |
| * from the point of perigee. |
| * |
| * @param eccentricity The eccentricity of the orbit |
| * |
| * @return The true anomaly (longitude) measured in radians |
| */ |
| private double trueAnomaly(double meanAnomaly, double eccentricity) |
| { |
| // First, solve Kepler's equation iteratively |
| double delta; |
| double E = meanAnomaly; |
| do { |
| delta = E - eccentricity * Math.sin(E) - meanAnomaly; |
| E = E - delta / (1 - eccentricity * Math.cos(E)); |
| } |
| while (Math.abs(delta) > accuracy); |
| |
| return 2.0 * Math.atan( Math.tan(E/2) * Math.sqrt( (1+eccentricity) |
| /(1-eccentricity) ) ); |
| } |
| |
| static private final double accuracy = 0.01 * PI/180; // 0.01 degrees |
| |
| /** |
| * Return the obliquity of the ecliptic (the angle between the ecliptic |
| * and the earth's equator) at the current time. This varies due to |
| * the precession of the earth's axis. |
| * |
| * @return the obliquity of the ecliptic relative to the equator, |
| * measured in radians. |
| */ |
| private double eclipticObliquity() { |
| if (eclipObliquity == INVALID) { |
| final double epoch = 2451545.0; // 2000 AD, January 1.5 |
| |
| double T = (getJulianDay() - epoch) / 36525; |
| |
| eclipObliquity = 23.439292 |
| - 46.815/3600 * T |
| - 0.0006 * T*T |
| + 0.00181 * T*T*T; |
| |
| eclipObliquity *= DEG_RAD; |
| } |
| return eclipObliquity; |
| } |
| |
| |
| //------------------------------------------------------------------------- |
| // Private data |
| //------------------------------------------------------------------------- |
| |
| /** |
| * Current time in milliseconds since 1/1/1970 AD |
| * @see java.util.Date#getTime |
| */ |
| private long time; |
| |
| /* These aren't used yet, but they'll be needed for sunset calculations |
| * and equatorial to horizon coordinate conversions |
| */ |
| private double fLongitude = 0.0; |
| private double fLatitude = 0.0; |
| private long fGmtOffset = 0; |
| |
| // |
| // The following fields are used to cache calculated results for improved |
| // performance. These values all depend on the current time setting |
| // of this object, so the clearCache method is provided. |
| // |
| static final private double INVALID = Double.MIN_VALUE; |
| |
| private transient double julianDay = INVALID; |
| private transient double julianCentury = INVALID; |
| private transient double sunLongitude = INVALID; |
| private transient double meanAnomalySun = INVALID; |
| private transient double moonLongitude = INVALID; |
| private transient double moonEclipLong = INVALID; |
| private transient double meanAnomalyMoon = INVALID; |
| private transient double eclipObliquity = INVALID; |
| private transient double siderealT0 = INVALID; |
| private transient double siderealTime = INVALID; |
| |
| private transient Equatorial moonPosition = null; |
| |
| private void clearCache() { |
| julianDay = INVALID; |
| julianCentury = INVALID; |
| sunLongitude = INVALID; |
| meanAnomalySun = INVALID; |
| moonLongitude = INVALID; |
| moonEclipLong = INVALID; |
| meanAnomalyMoon = INVALID; |
| eclipObliquity = INVALID; |
| siderealTime = INVALID; |
| siderealT0 = INVALID; |
| moonPosition = null; |
| } |
| |
| private static void out(String s) { |
| System.out.println(s); |
| } |
| |
| private static String deg(double rad) { |
| return Double.toString(rad * RAD_DEG); |
| } |
| |
| private static String hours(long ms) { |
| return Double.toString((double)ms / HOUR_MS) + " hours"; |
| } |
| public String local(long localMillis) { |
| return new Date(localMillis - TimeZone.getDefault().getRawOffset()).toString(); |
| } |
| |
| |
| /** |
| * Represents the position of an object in the sky relative to the ecliptic, |
| * the plane of the earth's orbit around the Sun. |
| * This is a spherical coordinate system in which the latitude |
| * specifies the position north or south of the plane of the ecliptic. |
| * The longitude specifies the position along the ecliptic plane |
| * relative to the "First Point of Aries", which is the Sun's position in the sky |
| * at the Vernal Equinox. |
| * <p> |
| * Note that Ecliptic objects are immutable and cannot be modified |
| * once they are constructed. This allows them to be passed and returned by |
| * value without worrying about whether other code will modify them. |
| * |
| * @see CalendarAstronomer.Equatorial |
| * @see CalendarAstronomer.Horizon |
| */ |
| public static final class Ecliptic { |
| /** |
| * Constructs an Ecliptic coordinate object. |
| * <p> |
| * @param lat The ecliptic latitude, measured in radians. |
| * @param lon The ecliptic longitude, measured in radians. |
| */ |
| public Ecliptic(double lat, double lon) { |
| latitude = lat; |
| longitude = lon; |
| } |
| |
| /** |
| * Return a string representation of this object |
| */ |
| public String toString() { |
| return Double.toString(longitude*RAD_DEG) + "," + (latitude*RAD_DEG); |
| } |
| |
| /** |
| * The ecliptic latitude, in radians. This specifies an object's |
| * position north or south of the plane of the ecliptic, |
| * with positive angles representing north. |
| */ |
| public final double latitude; |
| |
| /** |
| * The ecliptic longitude, in radians. |
| * This specifies an object's position along the ecliptic plane |
| * relative to the "First Point of Aries", which is the Sun's position |
| * in the sky at the Vernal Equinox, |
| * with positive angles representing east. |
| * <p> |
| * A bit of trivia: the first point of Aries is currently in the |
| * constellation Pisces, due to the precession of the earth's axis. |
| */ |
| public final double longitude; |
| }; |
| |
| /** |
| * Represents the position of an |
| * object in the sky relative to the plane of the earth's equator. |
| * The <i>Right Ascension</i> specifies the position east or west |
| * along the equator, relative to the sun's position at the vernal |
| * equinox. The <i>Declination</i> is the position north or south |
| * of the equatorial plane. |
| * <p> |
| * Note that Equatorial objects are immutable and cannot be modified |
| * once they are constructed. This allows them to be passed and returned by |
| * value without worrying about whether other code will modify them. |
| * |
| * @see CalendarAstronomer.Ecliptic |
| * @see CalendarAstronomer.Horizon |
| */ |
| public static final class Equatorial { |
| /** |
| * Constructs an Equatorial coordinate object. |
| * <p> |
| * @param asc The right ascension, measured in radians. |
| * @param dec The declination, measured in radians. |
| */ |
| public Equatorial(double asc, double dec) { |
| ascension = asc; |
| declination = dec; |
| } |
| |
| /** |
| * Return a string representation of this object, with the |
| * angles measured in degrees. |
| */ |
| public String toString() { |
| return Double.toString(ascension*RAD_DEG) + "," + (declination*RAD_DEG); |
| } |
| |
| /** |
| * Return a string representation of this object with the right ascension |
| * measured in hours, minutes, and seconds. |
| */ |
| public String toHmsString() { |
| return radToHms(ascension) + "," + radToDms(declination); |
| } |
| |
| /** |
| * The right ascension, in radians. |
| * This is the position east or west along the equator |
| * relative to the sun's position at the vernal equinox, |
| * with positive angles representing East. |
| */ |
| public final double ascension; |
| |
| /** |
| * The declination, in radians. |
| * This is the position north or south of the equatorial plane, |
| * with positive angles representing north. |
| */ |
| public final double declination; |
| }; |
| |
| /** |
| * Represents the position of an object in the sky relative to |
| * the local horizon. |
| * The <i>Altitude</i> represents the object's elevation above the horizon, |
| * with objects below the horizon having a negative altitude. |
| * The <i>Azimuth</i> is the geographic direction of the object from the |
| * observer's position, with 0 representing north. The azimuth increases |
| * clockwise from north. |
| * <p> |
| * Note that Horizon objects are immutable and cannot be modified |
| * once they are constructed. This allows them to be passed and returned by |
| * value without worrying about whether other code will modify them. |
| * |
| * @see CalendarAstronomer.Ecliptic |
| * @see CalendarAstronomer.Equatorial |
| */ |
| public static final class Horizon { |
| /** |
| * Constructs a Horizon coordinate object. |
| * <p> |
| * @param alt The altitude, measured in radians above the horizon. |
| * @param azim The azimuth, measured in radians clockwise from north. |
| */ |
| public Horizon(double alt, double azim) { |
| altitude = alt; |
| azimuth = azim; |
| } |
| |
| /** |
| * Return a string representation of this object, with the |
| * angles measured in degrees. |
| */ |
| public String toString() { |
| return Double.toString(altitude*RAD_DEG) + "," + (azimuth*RAD_DEG); |
| } |
| |
| /** The object's altitude above the horizon, in radians. */ |
| public final double altitude; |
| |
| /** The object's direction, in radians clockwise from north. */ |
| public final double azimuth; |
| }; |
| |
| static private String radToHms(double angle) { |
| int hrs = (int) (angle*RAD_HOUR); |
| int min = (int)((angle*RAD_HOUR - hrs) * 60); |
| int sec = (int)((angle*RAD_HOUR - hrs - min/60.0) * 3600); |
| |
| return Integer.toString(hrs) + "h" + min + "m" + sec + "s"; |
| } |
| |
| static private String radToDms(double angle) { |
| int deg = (int) (angle*RAD_DEG); |
| int min = (int)((angle*RAD_DEG - deg) * 60); |
| int sec = (int)((angle*RAD_DEG - deg - min/60.0) * 3600); |
| |
| return Integer.toString(deg) + "\u00b0" + min + "'" + sec + "\""; |
| } |
| } |
