Package gaiasky.util.coord

Class AstroUtils

java.lang.Object

gaiasky.util.coord.AstroUtils

public class AstroUtils
extends Object

Astronomical utilities. Contains functions to convert Julian dates, reference systems, and more.

Field Summary

Fields

Modifier and Type	Field	Description
static final long	J2000_MS	Milliseconds of J2000 in the scale of Instant.
static final double	JD_J2000	Julian date of reference epoch J2000 = JD2451544.5 = 2000-01-01T00:00:00Z.
static final double	JD_J2010	Julian date of reference epoch J2010 = JD2455197.5 = 2010-01-01T00:00:00Z.
static final double	JD_J2015	Julian date of reference epoch J2015.0 = JD2457023.5 = 2015-01-01T00:00:00Z.
static final double	JD_J2015_5	Julian date of reference epoch J2015.5 = JD2457206.125 = 2015-01-01T00:00:00Z.
static final double	JD_TO_Y	Julian days per year.

Constructor Summary

Constructors

Constructor	Description
AstroUtils()

Method Summary

Modifier and Type	Method	Description
static double	absoluteMagnitudeToPseudoSize(double absMag)	Computes the pseudo-size of a star from the absolute magnitude.
static double	absoluteToApparentMagnitude(double distPc, double absMag)	Converts an absolute magnitude to an apparent magnitude at the given distance in parsecs.
static double	apparentToAbsoluteMagnitude(double distPc, double appMag)	Converts an apparent magnitude to an absolute magnitude given the distance in parsecs.
static long[]	getCalendarDay(double julianDate)	Gets the Gregorian calendar quantities given the Julian date.
static long[]	getDayQuantities(double dayFraction)	Deprecated. Not used anymore.
static double	getDaysSince(Instant date, double epoch_jd)	Returns the elapsed days since the given julian date jd until the given date.
static double	getDaysSinceJ2000(Instant date)	Returns the elapsed days since the epoch J2000 until the given date.
static double	getJulianDate(double refEpoch)	Get julian date from a double reference epoch, as a Gregorian calendar year plus fraction.
static double	getJulianDate(Instant instant)	Gets the Julian date from a given Instant.
static double	getJulianDateCache(Instant instant)	Gets the Julian Date for the given Instant.
static double	getJulianDateUTC(int year, int month, int day, int hour, int min, int sec, int nanos)	Computes the Julian Date (JD) for a given date and time with nanosecond precision, using either the Julian or Gregorian calendar depending on the date.
static double	getJulianDayNumberBook(int year, int month, int day)	Deprecated. This does not work well!
static double	getJulianDayNumberGregorian(int year, int month, int day)	Determine Julian day number from Gregorian calendar date.
static double	getJulianDayNumberJulianCalendar(int year, int month, int day)	Returns the Julian day number of a date in the Julian calendar.
static double	getMsSince(Instant date, double epoch_jd)	Returns the elapsed milliseconds since the given julian date jd until the given date.
static String	getSpectralType(float tEff)	Get the spectral type from the effective temperature for main sequence stars.
static double	getSunLongitude(Instant date)	Returns the Sun's ecliptic longitude in degrees for the given time.
static boolean	isLeapYearGregorian(int year)	Is a given year in the Gregorian calendar a leap year ?
static Instant	julianDateToInstant(double jd)
static double	obliquity(double julianDate)	Returns the obliquity of the ecliptic (inclination of the Earth's axis of rotation) for a given date, in degrees
static void	plutoEclipticCoordinates(Instant date, Vector3Q out)	Spherical ecliptic coordinates of Pluto at the given date.
static double	T(double julianDate)	Time T measured in Julian centuries from the Epoch J2000.0.
static double	tau(double julianDate)

Methods inherited from class java.lang.Object

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

Field Details

JD_TO_Y

public static final double JD_TO_Y

Julian days per year.

See Also:

• Constant Field Values

JD_J2000

public static final double JD_J2000

Julian date of reference epoch J2000 = JD2451544.5 = 2000-01-01T00:00:00Z.

JD_J2010

public static final double JD_J2010

Julian date of reference epoch J2010 = JD2455197.5 = 2010-01-01T00:00:00Z.

JD_J2015

public static final double JD_J2015

Julian date of reference epoch J2015.0 = JD2457023.5 = 2015-01-01T00:00:00Z.

JD_J2015_5

public static final double JD_J2015_5

Julian date of reference epoch J2015.5 = JD2457206.125 = 2015-01-01T00:00:00Z.

J2000_MS

public static final long J2000_MS

Milliseconds of J2000 in the scale of Instant. This is the number of milliseconds elapsed since 1970-01-01T00:00:00Z (UTC) until 2000-01-01T00:00:00Z (UTC).

Constructor Details

AstroUtils

public AstroUtils()

Method Details

getJulianDate

public static double getJulianDate(double refEpoch)

Get julian date from a double reference epoch, as a Gregorian calendar year plus fraction.

Parameters:

refEpoch - The reference epoch as a Gregorian calendar year.

Returns:

The julian date.

getSunLongitude

public static double getSunLongitude(Instant date)

Returns the Sun's ecliptic longitude in degrees for the given time. Caches the last Sun's longitude for future use.

Parameters:

date - The time for which the longitude must be calculated.

Returns:

The Sun's longitude in [deg].

getJulianDateUTC

public static double getJulianDateUTC(int year,
 int month,
 int day,
 int hour,
 int min,
 int sec,
 int nanos)

Computes the Julian Date (JD) for a given date and time with nanosecond precision, using either the Julian or Gregorian calendar depending on the date.

The calendar transition is determined by comparing the input against a predefined gregorianSwitch Instant, after which the Gregorian calendar is used. The input quantities are assumed to be in UTC.

Parameters:

year - the year component of the date

month - the month component of the date (1 = January, ..., 12 = December)

day - the day of the month (1-31)

hour - the hour of the day (0–23)

min - the minute of the hour (0–59)

sec - the second of the minute (0–59)

nanos - the nanosecond of the second (0–999,999,999)

Returns:

the Julian Date corresponding to the given date and time

Throws:

DateTimeException - if the date-time values are invalid

getJulianDateCache

public static double getJulianDateCache(Instant instant)

Gets the Julian Date for the given Instant. It uses a cache.

Parameters:

instant - The date.

Returns:

The Julian Date.

getJulianDate

public static double getJulianDate(Instant instant)

Gets the Julian date from a given Instant. Instants are by definition in UTC.

Parameters:

instant - The instant.

Returns:

The Julian date.

getDaysSinceJ2000

public static double getDaysSinceJ2000(Instant date)

Returns the elapsed days since the epoch J2000 until the given date. Can be negative.

Parameters:

date - The date.

Returns:

The elapsed days.

getMsSince

public static double getMsSince(Instant date,
 double epoch_jd)

Returns the elapsed milliseconds since the given julian date jd until the given date. Can be negative.

Parameters:

date - The date.

epoch_jd - The reference epoch in julian days.

Returns:

The elapsed milliseconds.

getDaysSince

public static double getDaysSince(Instant date,
 double epoch_jd)

Returns the elapsed days since the given julian date jd until the given date. Can be negative.

Parameters:

date - The date.

epoch_jd - The reference epoch in julian days.

Returns:

The elapsed days

getCalendarDay

public static long[] getCalendarDay(double julianDate)

Gets the Gregorian calendar quantities given the Julian date.

Parameters:

julianDate - The Julian date.

Returns:

Vector with [year, month, day, hour, min, sec, nanos].

getJulianDayNumberBook

@Deprecated
public static double getJulianDayNumberBook(int year,
 int month,
 int day)

Deprecated.

This does not work well!

Returns the Julian day number. Uses the method shown in "Astronomical Algorithms" by Jean Meeus.

Parameters:

year - The year

month - The month in [1:12]

day - The day in the month, starting at 1

Returns:

The Julian date

getJulianDayNumberJulianCalendar

public static double getJulianDayNumberJulianCalendar(int year,
 int month,
 int day)

Returns the Julian day number of a date in the Julian calendar. Uses Wikipedia's algorithm.

Parameters:

year - The year

month - The month in [1:12]

day - The day in the month, starting at 1

Returns:

The Julian date

See Also:

• http://en.wikipedia.org/wiki/Julian_day

isLeapYearGregorian

public static boolean isLeapYearGregorian(int year)

Is a given year in the Gregorian calendar a leap year ?

Parameters:

year - The year.

Returns:

Whether the year in the Gregorian calendar is a leap year.

getJulianDayNumberGregorian

public static double getJulianDayNumberGregorian(int year,
 int month,
 int day)

Determine Julian day number from Gregorian calendar date.

Parameters:

year - The year.

month - The month.

day - The day.

Returns:

The julian day number.

julianDateToInstant

public static Instant julianDateToInstant(double jd)

getDayQuantities

@Deprecated
public static long[] getDayQuantities(double dayFraction)

Deprecated.

Not used anymore.

Gets the day quantities from the day fraction

Parameters:

dayFraction - The day fraction.

Returns:

[hours, minutes, seconds, nanos].

obliquity

public static double obliquity(double julianDate)

Returns the obliquity of the ecliptic (inclination of the Earth's axis of rotation) for a given date, in degrees

Returns:

The obliquity in degrees

T

public static double T(double julianDate)

Time T measured in Julian centuries from the Epoch J2000.0.

Parameters:

julianDate - The julian date.

Returns:

The time in julian centuries.

tau

public static double tau(double julianDate)

apparentToAbsoluteMagnitude

public static double apparentToAbsoluteMagnitude(double distPc,
 double appMag)

Converts an apparent magnitude to an absolute magnitude given the distance in parsecs.

Parameters:

distPc - The distance to the star in parsecs.

appMag - The apparent magnitude.

Returns:

The absolute magnitude.

absoluteToApparentMagnitude

public static double absoluteToApparentMagnitude(double distPc,
 double absMag)

Converts an absolute magnitude to an apparent magnitude at the given distance in parsecs.

Parameters:

distPc - The distance to the star in parsecs.

absMag - The absolute magnitude.

Returns:

The apparent magnitude at the given distance.

absoluteMagnitudeToPseudoSize

public static double absoluteMagnitudeToPseudoSize(double absMag)

Computes the pseudo-size of a star from the absolute magnitude.

Parameters:

absMag - The absolute magnitude of the star.

Returns:

The pseudo-size of this star, mainly used for rendering purposes. It has no physical meaning and has no relation to the actual physical size of the star.

getSpectralType

public static String getSpectralType(float tEff)

Get the spectral type from the effective temperature for main sequence stars. More info: see here.

plutoEclipticCoordinates

public static void plutoEclipticCoordinates(Instant date,
 Vector3Q out)

Spherical ecliptic coordinates of Pluto at the given date.

Parameters:

date - The date.

out - The out vector with [lambda, beta, r] in radians and kilometres.