Lunar phase and position

PyAstronomy.pyasl.moonpos(jd, radian=False)

Computes RA and DEC of the Moon at given Julian date(s).

Parameters
jdfloat or array

The Julian date.

radianboolean, optional

If True, results are returned in RADIAN instead of DEGREES. Default is False.

Returns
RAfloat or array

Right ascension of the moon for given JD(s) in DEGREES.

DECfloat or array

Declination of the moon for given JD(s) in DEGREES.

DISTANCEfloat or array

Distance of the moon from the Earth for given JD(s) in KILOMETERS.

GEOLONGITUDEfloat or array

Apparent longitude of the moon for given JD(s) in DEGREES.

GEOLATITUDEfloat or array

Apparent latitude of the moon for given JD(s) in DEGREES.

Notes

Note

This function was ported from the IDL Astronomy User’s Library.

IDL - Documentation

PRO MOONPOS, jd, ra, dec, dis, geolong, geolat, RADIAN = radian

NAME:

MOONPOS

PURPOSE:

To compute the RA and Dec of the Moon at specified Julian date(s).

CALLING SEQUENCE:

MOONPOS, jd, ra, dec, dis, geolong, geolat, [/RADIAN ]

INPUTS:

JD - Julian ephemeris date, scalar or vector, double precision suggested

OUTPUTS:
Ra - Apparent right ascension of the moon in DEGREES, referred to the

true equator of the specified date(s)

Dec - The declination of the moon in DEGREES Dis - The Earth-moon distance in kilometers (between the center of the

Earth and the center of the Moon).

Geolong - Apparent longitude of the moon in DEGREES, referred to the

ecliptic of the specified date(s)

Geolat - Apparent longitude of the moon in DEGREES, referred to the

ecliptic of the specified date(s)

The output variables will all have the same number of elements as the input Julian date vector, JD. If JD is a scalar then the output variables will be also.

OPTIONAL INPUT KEYWORD:
/RADIAN - If this keyword is set and non-zero, then all output variables

are given in Radians rather than Degrees

EXAMPLES:

  1. Find the position of the moon on April 12, 1992

IDL> jdcnv,1992,4,12,0,jd ;Get Julian date IDL> moonpos, jd, ra ,dec ;Get RA and Dec of moon IDL> print,adstring(ra,dec,1)

==> 08 58 45.23 +13 46 6.1

This is within 1” from the position given in the Astronomical Almanac

  1. Plot the Earth-moon distance for every day at 0 TD in July, 1996

IDL> jdcnv,1996,7,1,0,jd ;Get Julian date of July 1 IDL> moonpos,jd+dindgen(31), ra, dec, dis ;Position at all 31 days IDL> plot,indgen(31),dis, /YNOZ

METHOD:

Derived from the Chapront ELP2000/82 Lunar Theory (Chapront-Touze’ and Chapront, 1983, 124, 50), as described by Jean Meeus in Chapter 47 of ``Astronomical Algorithms’’ (Willmann-Bell, Richmond), 2nd edition, 1998. Meeus quotes an approximate accuracy of 10” in longitude and 4” in latitude, but he does not give the time range for this accuracy.

Comparison of this IDL procedure with the example in ``Astronomical Algorithms’’ reveals a very small discrepancy (~1 km) in the distance computation, but no difference in the position calculation.

This procedure underwent a major rewrite in June 1996, and the new calling sequence is incompatible with the old (e.g. angles now returned in degrees instead of radians).

PROCEDURES CALLED:

CIRRANGE, ISARRAY(), NUTATE, TEN() - from IDL Astronomy Library POLY() - from IDL User’s Library

MODIFICATION HISTORY:

Written by Michael R. Greason, STX, 31 October 1988. Major rewrite, new (incompatible) calling sequence, much improved

accuracy, W. Landsman Hughes STX June 1996

Added /RADIAN keyword W. Landsman August 1997 Converted to IDL V5.0 W. Landsman September 1997 Use improved expressions for L’,D,M,M’, and F given in 2nd edition of

Meeus (very slight change), W. Landsman November 2000

Avoid 32767 overflow W. Landsman January 2005

Example: Finding the position of the Moon

from __future__ import print_function, division
import datetime
from PyAstronomy import pyasl
import numpy as np

# Convert calendar date to JD
# using the datetime package
jd = datetime.datetime(2013, 4, 16)
jd = pyasl.jdcnv(jd)
jd = np.arange(jd, jd + 20, 1)
# Calculate Moon positions
res = pyasl.moonpos(jd)

print("%15s  %8s  %8s  %11s  %8s  %8s" %
      ("JD", "RA", "DEC", "DIST", "GEOLON", "GEOLAT"))
print("%15s  %8s  %8s  %11s  %8s  %8s" %
      ("[d]", "[deg]", "[deg]", "[km]", "[deg]", "[deg]"))
for i in range(jd.size):
    print("%15.4f  %8.4f  %8.4f  %11.4f  %8.4f  %8.4f" %
          (jd[i], res[0][i], res[1][i], res[2][i], res[3][i], res[4][i]))
PyAstronomy.pyasl.moonphase(jd)

Computes the illuminated fraction of the Moon at given Julian date(s).

Parameters
jdfloat or array

The Julian date.

Returns
Fractionfloat or array

The illuminated fraction [0 - 1] of the Moon. Has the same size as jd.

Notes

Note

This function was ported from the IDL Astronomy User’s Library.

IDL - Documentation

NAME:

MPHASE

PURPOSE:

Return the illuminated fraction of the Moon at given Julian date(s)

CALLING SEQUENCE:

MPHASE, jd, k

INPUT:

JD - Julian date, scalar or vector, double precision recommended

OUTPUT:
k - illuminated fraction of Moon’s disk (0.0 < k < 1.0), same number

of elements as jd. k = 0 indicates a new moon, while k = 1 for a full moon.

EXAMPLE:

Plot the illuminated fraction of the moon for every day in July 1996 at 0 TD (~Greenwich noon).

IDL> jdcnv, 1996, 7, 1, 0, jd ;Get Julian date of July 1 IDL> mphase, jd+dindgen(31), k ;Moon phase for all 31 days IDL> plot, indgen(31),k ;Plot phase vs. July day number

Example: Find the Moon’s illuminated fraction

from __future__ import print_function, division
import datetime
from PyAstronomy import pyasl
import numpy as np

# Convert calendar date to JD
# using the datetime package
jd = datetime.datetime(2013, 4, 16)
jd = pyasl.jdcnv(jd)
jd = np.arange(jd, jd+20, 1)
mp = pyasl.moonphase(jd)

print("%15s  %3s" % ("JD", "Phase"))
for i in range(jd.size):
    print("%15.4f  %3d%%" % (jd[i], mp[i]*100.))