com.ibm.util
Class CalendarAstronomer

java.lang.Object
  |
  +--com.ibm.util.CalendarAstronomer

public class CalendarAstronomer
extends java.lang.Object

CalendarAstronomer 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.

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 CalendarAstronomer object has a time property that determines the date and time for which its calculations are performed. You can set and retrieve this property with setDate, getDate and related methods.

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 Practical Astronomy With Your Calculator, 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.

WARNING: 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 IslamicCalendar and ChineseCalendar.

Author:
Laura Werner, Alan Liu

Inner Class Summary
static class CalendarAstronomer.Ecliptic
          Represents the position of an object in the sky relative to the ecliptic, the plane of the earth's orbit around the Sun.
static class CalendarAstronomer.Equatorial
          Represents the position of an object in the sky relative to the plane of the earth's equator.
static class CalendarAstronomer.Horizon
          Represents the position of an object in the sky relative to the local horizon.
 
Field Summary
static com.ibm.util.CalendarAstronomer.SolarLongitude AUTUMN_EQUINOX
          Constant representing the autumnal equinox.
static long DAY_MS
          The number of milliseconds in one day.
static com.ibm.util.CalendarAstronomer.MoonAge FIRST_QUARTER
          Constant representing the moon's first quarter.
static com.ibm.util.CalendarAstronomer.MoonAge FULL_MOON
          Constant representing a full moon.
static int HOUR_MS
          The number of milliseconds in one hour.
static long JULIAN_EPOCH_MS
          The start of the julian day numbering scheme used by astronomers, which is 1/1/4713 BC (Julian), 12:00 GMT.
static com.ibm.util.CalendarAstronomer.MoonAge LAST_QUARTER
          Constant representing the moon's last quarter.
static int MINUTE_MS
          The number of milliseconds in one minute.
static com.ibm.util.CalendarAstronomer.MoonAge NEW_MOON
          Constant representing a new moon.
static int SECOND_MS
          The number of milliseconds in one second.
static double SIDEREAL_DAY
          The number of standard hours in one sidereal day.
static double SIDEREAL_MONTH
          The average number of days it takes for the moon to return to the same ecliptic longitude relative to the stellar background.
static double SIDEREAL_YEAR
          The average number of days it takes for the sun to return to the same position against the fixed stellar background.
static double SOLAR_DAY
          The number of sidereal hours in one mean solar day.
static com.ibm.util.CalendarAstronomer.SolarLongitude SUMMER_SOLSTICE
          Constant representing the summer solstice.
static double SYNODIC_MONTH
          The average number of solar days from one new moon to the next.
static double TROPICAL_YEAR
          The average number number of days between successive vernal equinoxes.
static com.ibm.util.CalendarAstronomer.SolarLongitude VERNAL_EQUINOX
          Constant representing the vernal equinox.
static com.ibm.util.CalendarAstronomer.SolarLongitude WINTER_SOLSTICE
          Constant representing the winter solstice.
 
Constructor Summary
CalendarAstronomer()
          Construct a new CalendarAstronomer object that is initialized to the current date and time.
CalendarAstronomer(java.util.Date d)
          Construct a new CalendarAstronomer object that is initialized to the specified date and time.
CalendarAstronomer(double longitude, double latitude)
          Construct a new CalendarAstronomer object with the given latitude and longitude.
CalendarAstronomer(long aTime)
          Construct a new CalendarAstronomer object that is initialized to the specified time.
 
Method Summary
 CalendarAstronomer.Equatorial eclipticToEquatorial(CalendarAstronomer.Ecliptic ecliptic)
          Convert from ecliptic to equatorial coordinates.
 CalendarAstronomer.Equatorial eclipticToEquatorial(double eclipLong)
          Convert from ecliptic longitude to equatorial coordinates.
 CalendarAstronomer.Equatorial eclipticToEquatorial(double eclipLong, double eclipLat)
          Convert from ecliptic to equatorial coordinates.
 CalendarAstronomer.Horizon eclipticToHorizon(double eclipLong)
           
 java.util.Date getDate()
          Get the current time of this CalendarAstronomer object, represented as a Date object.
 double getGreenwichSidereal()
          Returns the current Greenwich sidereal time, measured in hours
 double getJulianCentury()
          Return this object's time expressed in julian centuries: the number of centuries after 1/1/1900 AD, 12:00 GMT
 double getJulianDay()
          Get the current time of this CalendarAstronomer object, expressed as a "julian day number", which is the number of elapsed days since 1/1/4713 BC (Julian), 12:00 GMT.
 double getLocalSidereal()
          Returns the current local sidereal time, measured in hours
 double getMoonAge()
          The "age" of the moon at the time specified in this object.
 double getMoonPhase()
          Calculate the phase of the moon at the time set in this object.
 CalendarAstronomer.Equatorial getMoonPosition()
          The position of the moon at the time set on this object, in equatorial coordinates.
 long getMoonRiseSet(boolean rise)
          Returns the time (GMT) of sunrise or sunset on the local date to which this calendar is currently set.
 long getMoonTime(com.ibm.util.CalendarAstronomer.MoonAge desired, boolean next)
          Find the next or previous time at which the moon will be in the desired phase.
 long getMoonTime(double desired, boolean next)
          Find the next or previous time at which the Moon's ecliptic longitude will have the desired value.
 double getSunLongitude()
          The longitude of the sun at the time specified by this object.
 CalendarAstronomer.Equatorial getSunPosition()
          The position of the sun at this object's current date and time, in equatorial coordinates.
 long getSunRiseSet(boolean rise)
          Returns the time (GMT) of sunrise or sunset on the local date to which this calendar is currently set.
 long getSunTime(com.ibm.util.CalendarAstronomer.SolarLongitude desired, boolean next)
          Find the next time at which the sun's ecliptic longitude will have the desired value.
 long getSunTime(double desired, boolean next)
          Find the next time at which the sun's ecliptic longitude will have the desired value.
 long getTime()
          Get the current time of this CalendarAstronomer object, represented as the number of milliseconds since 1/1/1970 AD 0:00 GMT (Gregorian).
 java.lang.String local(long localMillis)
           
 void setDate(java.util.Date date)
          Set the current date and time of this CalendarAstronomer object.
 void setJulianDay(double jdn)
          Set the current date and time of this CalendarAstronomer object.
 void setTime(long aTime)
          Set the current date and time of this CalendarAstronomer object.
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

SIDEREAL_DAY

public static final double SIDEREAL_DAY
The number of standard hours in one sidereal day. Approximately 24.93.

SOLAR_DAY

public static final double SOLAR_DAY
The number of sidereal hours in one mean solar day. Approximately 24.07.

SYNODIC_MONTH

public static final double SYNODIC_MONTH
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 Also:
SIDEREAL_MONTH

SIDEREAL_MONTH

public static final double SIDEREAL_MONTH
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 Also:
SYNODIC_MONTH

TROPICAL_YEAR

public static final double TROPICAL_YEAR
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 Also:
SIDEREAL_YEAR

SIDEREAL_YEAR

public static final double SIDEREAL_YEAR
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 Also:
TROPICAL_YEAR

SECOND_MS

public static final int SECOND_MS
The number of milliseconds in one second.

MINUTE_MS

public static final int MINUTE_MS
The number of milliseconds in one minute.

HOUR_MS

public static final int HOUR_MS
The number of milliseconds in one hour.

DAY_MS

public static final long DAY_MS
The number of milliseconds in one day.

JULIAN_EPOCH_MS

public static final long JULIAN_EPOCH_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 not the same thing. Also note that julian days start at noon, not midnight.

VERNAL_EQUINOX

public static final com.ibm.util.CalendarAstronomer.SolarLongitude VERNAL_EQUINOX
Constant representing the vernal equinox. For use with getSunTime. Note: In this case, "vernal" refers to the northern hemisphere's seasons.

SUMMER_SOLSTICE

public static final com.ibm.util.CalendarAstronomer.SolarLongitude SUMMER_SOLSTICE
Constant representing the summer solstice. For use with getSunTime. Note: In this case, "summer" refers to the northern hemisphere's seasons.

AUTUMN_EQUINOX

public static final com.ibm.util.CalendarAstronomer.SolarLongitude AUTUMN_EQUINOX
Constant representing the autumnal equinox. For use with getSunTime. Note: In this case, "autumn" refers to the northern hemisphere's seasons.

WINTER_SOLSTICE

public static final com.ibm.util.CalendarAstronomer.SolarLongitude WINTER_SOLSTICE
Constant representing the winter solstice. For use with getSunTime. Note: In this case, "winter" refers to the northern hemisphere's seasons.

NEW_MOON

public static final com.ibm.util.CalendarAstronomer.MoonAge NEW_MOON
Constant representing a new moon. For use with getMoonTime

FIRST_QUARTER

public static final com.ibm.util.CalendarAstronomer.MoonAge FIRST_QUARTER
Constant representing the moon's first quarter. For use with getMoonTime

FULL_MOON

public static final com.ibm.util.CalendarAstronomer.MoonAge FULL_MOON
Constant representing a full moon. For use with getMoonTime

LAST_QUARTER

public static final com.ibm.util.CalendarAstronomer.MoonAge LAST_QUARTER
Constant representing the moon's last quarter. For use with getMoonTime
Constructor Detail

CalendarAstronomer

public CalendarAstronomer()
Construct a new CalendarAstronomer object that is initialized to the current date and time.

CalendarAstronomer

public CalendarAstronomer(java.util.Date d)
Construct a new CalendarAstronomer object that is initialized to the specified date and time.

CalendarAstronomer

public CalendarAstronomer(long aTime)
Construct a new CalendarAstronomer object that is initialized to the specified time. The time is expressed as a number of milliseconds since January 1, 1970 AD (Gregorian).
See Also:
Date.getTime()

CalendarAstronomer

public CalendarAstronomer(double longitude,
                          double latitude)
Construct a new CalendarAstronomer object with the given latitude and longitude. The object's time is set to the current date and time.

Parameters:
longitude - The desired longitude, in degrees east of the Greenwich meridian.
latitude - The desired latitude, in degrees. Positive values signify North, negative South.
See Also:
Date.getTime()
Method Detail

setTime

public void setTime(long aTime)
Set the current date and time of this CalendarAstronomer object. All astronomical calculations are performed based on this time setting.
Parameters:
aTime - the date and time, expressed as the number of milliseconds since 1/1/1970 0:00 GMT (Gregorian).
See Also:
setDate(java.util.Date), getTime()

setDate

public void setDate(java.util.Date date)
Set the current date and time of this CalendarAstronomer object. All astronomical calculations are performed based on this time setting.
Parameters:
aTime - the time and date, expressed as a Date object.
See Also:
setTime(long), getDate()

setJulianDay

public void setJulianDay(double jdn)
Set the current date and time of this CalendarAstronomer object. All astronomical calculations are performed based on this time setting.
Parameters:
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 noon. To get the jdn for the corresponding midnight, subtract 0.5.
See Also:
getJulianDay(), JULIAN_EPOCH_MS

getTime

public long getTime()
Get the current time of this CalendarAstronomer object, represented as the number of milliseconds since 1/1/1970 AD 0:00 GMT (Gregorian).
See Also:
setTime(long), getDate()

getDate

public java.util.Date getDate()
Get the current time of this CalendarAstronomer object, represented as a Date object.
See Also:
setDate(java.util.Date), getTime()

getJulianDay

public double getJulianDay()
Get the current time of this CalendarAstronomer object, expressed as a "julian day number", which is the number of elapsed days since 1/1/4713 BC (Julian), 12:00 GMT.
See Also:
setJulianDay(double), JULIAN_EPOCH_MS

getJulianCentury

public double getJulianCentury()
Return this object's time expressed in julian centuries: the number of centuries after 1/1/1900 AD, 12:00 GMT
See Also:
getJulianDay()

getGreenwichSidereal

public double getGreenwichSidereal()
Returns the current Greenwich sidereal time, measured in hours

getLocalSidereal

public double getLocalSidereal()
Returns the current local sidereal time, measured in hours

eclipticToEquatorial

public final CalendarAstronomer.Equatorial eclipticToEquatorial(CalendarAstronomer.Ecliptic ecliptic)
Convert from ecliptic to equatorial coordinates.
Parameters:
ecliptic - A point in the sky in ecliptic coordinates.
Returns:
The corresponding point in equatorial coordinates.

eclipticToEquatorial

public final CalendarAstronomer.Equatorial eclipticToEquatorial(double eclipLong,
                                                                double eclipLat)
Convert from ecliptic to equatorial coordinates.
Parameters:
eclipLong - The ecliptic longitude
eclipLat - The ecliptic latitude
Returns:
The corresponding point in equatorial coordinates.

eclipticToEquatorial

public final CalendarAstronomer.Equatorial eclipticToEquatorial(double eclipLong)
Convert from ecliptic longitude to equatorial coordinates.
Parameters:
eclipLong - The ecliptic longitude
Returns:
The corresponding point in equatorial coordinates.

eclipticToHorizon

public CalendarAstronomer.Horizon eclipticToHorizon(double eclipLong)

getSunLongitude

public double getSunLongitude()
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.

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.


getSunPosition

public CalendarAstronomer.Equatorial getSunPosition()
The position of the sun at this object's current date and time, in equatorial coordinates.

getSunTime

public long getSunTime(double desired,
                       boolean next)
Find the next time at which the sun's ecliptic longitude will have the desired value.

getSunTime

public long getSunTime(com.ibm.util.CalendarAstronomer.SolarLongitude desired,
                       boolean next)
Find the next time at which the sun's ecliptic longitude will have the desired value.

getSunRiseSet

public long getSunRiseSet(boolean rise)
Returns the time (GMT) of sunrise or sunset on the local date to which this calendar is currently set.

getMoonPosition

public CalendarAstronomer.Equatorial getMoonPosition()
The position of the moon at the time set on this object, in equatorial coordinates.

getMoonAge

public double getMoonAge()
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 Also:
getMoonPhase()

getMoonPhase

public double getMoonPhase()
Calculate the phase of the moon at the time set in this object. The returned phase is a double in the range 0 <= phase < 1, interpreted as follows:
See Also:
getMoonAge()

getMoonTime

public long getMoonTime(double desired,
                        boolean next)
Find the next or previous time at which the Moon's ecliptic longitude will have the desired value.

Parameters:
desired - The desired longitude.
next - true if the next occurrance of the phase is desired, false for the previous occurrance.

getMoonTime

public long getMoonTime(com.ibm.util.CalendarAstronomer.MoonAge desired,
                        boolean next)
Find the next or previous time at which the moon will be in the desired phase.

Parameters:
desired - The desired phase of the moon.
next - true if the next occurrance of the phase is desired, false for the previous occurrance.

getMoonRiseSet

public long getMoonRiseSet(boolean rise)
Returns the time (GMT) of sunrise or sunset on the local date to which this calendar is currently set.

local

public java.lang.String local(long localMillis)


Copyright (c) 2001 IBM Corporation and others.