def helcorr(obs_long, obs_lat, obs_alt, ra2000, dec2000, jd, debug=False):
"""
Calculate barycentric velocity correction.
This function calculates the motion of an observer in
the direction of a star. In contract to :py:func:`baryvel`
and :py:func:`baryCorr`, the rotation of the Earth is
taken into account.
.. note:: This function was ported from the REDUCE IDL package.
See Piskunov & Valenti 2002, A&A 385, 1095 for a detailed
description of the package and/or visit
http://www.astro.uu.se/~piskunov/RESEARCH/REDUCE/
.. warning:: Contrary to the original implementation the longitude
increases toward the East and the right ascension is
given in degrees instead of hours. The JD is given as is,
in particular, nothing needs to be subtracted.
Parameters
----------
obs_long : float
Longitude of observatory (degrees, **eastern** direction is positive)
obs_lat : float
Latitude of observatory [deg]
obs_alt : float
Altitude of observatory [m]
ra2000 : float
Right ascension of object for epoch 2000.0 [deg]
dec2000 : float
Declination of object for epoch 2000.0 [deg]
jd : float
Julian date for the middle of exposure.
Returns
-------
Barycentric correction : float
The barycentric correction accounting for the rotation
of the Earth, the rotation of the Earth's center around
the Earth-Moon barycenter, and the motion of the Earth-Moon
barycenter around the center of the Sun [km/s].
HJD : float
Heliocentric Julian date for middle of exposure.
Notes
-----
:IDL REDUCE - Documentation:
Calculates heliocentric Julian date, barycentric and heliocentric radial
velocity corrections from:
INPUT:
<OBSLON> Longitude of observatory (degrees, western direction is positive)
<OBSLAT> Latitude of observatory (degrees)
<OBSALT> Altitude of observatory (meters)
<RA2000> Right ascension of object for epoch 2000.0 (hours)
<DE2000> Declination of object for epoch 2000.0 (degrees)
<JD> Julian date for the middle of exposure
[DEBUG=] set keyword to get additional results for debugging
OUTPUT:
<CORRECTION> barycentric correction - correction for rotation of earth,
rotation of earth center about the earth-moon barycenter, earth-moon
barycenter about the center of the Sun.
<HJD> Heliocentric Julian date for middle of exposure
Algorithms used are taken from the IRAF task noao.astutils.rvcorrect
and some procedures of the IDL Astrolib are used as well.
Accuracy is about 0.5 seconds in time and about 1 m/s in velocity.
History:
written by Peter Mittermayer, Nov 8,2003
2005-January-13 Kudryavtsev Made more accurate calculation of the sidereal time.
Conformity with MIDAS compute/barycorr is checked.
2005-June-20 Kochukhov Included precession of RA2000 and DEC2000 to current epoch
"""
from PyAstronomy.pyaC import degtorad
# This reverts the original longitude convention. After this,
# East longitudes are positive
obs_long = -obs_long
if jd < 2.4e6:
PE.warn(PE.PyAValError("The given Julian Date (" + str(jd) + ") is exceedingly small. Did you subtract 2.4e6?"))
# Covert JD to Gregorian calendar date
xjd = jd
year, month, day, ut = tuple(daycnv(xjd))
# Current epoch
epoch = year + month/12. + day/365.
# Precess ra2000 and dec2000 to current epoch, resulting ra is in degrees
ra = ra2000
dec = dec2000
ra, dec = precess(ra, dec, 2000.0, epoch)
# Calculate heliocentric julian date
rjd = jd-2.4e6
hjd = helio_jd(rjd, ra, dec) + 2.4e6
# DIURNAL VELOCITY (see IRAF task noao.astutil.rvcorrect)
# convert geodetic latitude into geocentric latitude to correct
# for rotation of earth
dlat = -(11.*60.+32.743)*np.sin(2.0*degtorad(obs_lat)) \
+1.1633*np.sin(4.0*degtorad(obs_lat)) - 0.0026*np.sin(6.0*degtorad(obs_lat))
lat = obs_lat + dlat/3600.0
# Calculate distance of observer from earth center
r = 6378160.0 * (0.998327073+0.001676438*np.cos(2.0*degtorad(lat)) \
-0.00000351 * np.cos(4.0*degtorad(lat)) + 0.000000008*np.cos(6.0*degtorad(lat))) \
+ obs_alt
# Calculate rotational velocity (perpendicular to the radius vector) in km/s
# 23.934469591229 is the sidereal day in hours for 1986
v = 2.*np.pi * (r/1000.) / (23.934469591229*3600.)
# Calculating local mean sidereal time (see astronomical almanach)
tu = (rjd-51545.0)/36525.0
gmst = 6.697374558 + ut + \
(236.555367908*(rjd-51545.0) + 0.093104*tu**2 - 6.2e-6*tu**3)/3600.0
lmst = idlMod(gmst-obs_long/15, 24)
# Projection of rotational velocity along the line of sight
vdiurnal = v*np.cos(degtorad(lat))*np.cos(degtorad(dec))*np.sin(degtorad(ra-lmst*15))
# BARICENTRIC and HELIOCENTRIC VELOCITIES
vh, vb = baryvel(xjd,0)
# Project to line of sight
vbar = vb[0]*np.cos(degtorad(dec))*np.cos(degtorad(ra)) + vb[1]*np.cos(degtorad(dec))*np.sin(degtorad(ra)) + \
vb[2]*np.sin(degtorad(dec))
vhel = vh[0]*np.cos(degtorad(dec))*np.cos(degtorad(ra)) + vh[1]*np.cos(degtorad(dec))*np.sin(degtorad(ra)) + \
vh[2]*np.sin(degtorad(dec))
# Use barycentric velocity for correction
corr = (vdiurnal + vbar)
if debug:
print ''
print '----- HELCORR.PRO - DEBUG INFO - START ----'
print '(obs_long (East positive),obs_lat,obs_alt) Observatory coordinates [deg,m]: ', -obs_long, obs_lat, obs_alt
print '(ra,dec) Object coordinates (for epoch 2000.0) [deg]: ', ra,dec
print '(ut) Universal time (middle of exposure) [hrs]: ', ut
print '(jd) Julian date (middle of exposure) (JD): ', jd
print '(hjd) Heliocentric Julian date (middle of exposure) (HJD): ', hjd
print '(gmst) Greenwich mean sidereal time [hrs]: ', idlMod(gmst, 24)
print '(lmst) Local mean sidereal time [hrs]: ', lmst
print '(dlat) Latitude correction [deg]: ', dlat
print '(lat) Geocentric latitude of observer [deg]: ', lat
print '(r) Distance of observer from center of earth [m]: ', r
print '(v) Rotational velocity of earth at the position of the observer [km/s]: ', v
print '(vdiurnal) Projected earth rotation and earth-moon revolution [km/s]: ', vdiurnal
print '(vbar) Barycentric velocity [km/s]: ', vbar
print '(vhel) Heliocentric velocity [km/s]: ', vhel
print '(corr) Vdiurnal+vbar [km/s]: ', corr
print '----- HELCORR.PRO - DEBUG INFO - END -----'
print ''
return corr, hjd
def baryvel(dje, deq):
"""
Calculate helio- and barycentric velocity.
.. note:: The "JPL" option present in IDL is not provided here.
Parameters
----------
dje : float
Julian ephemeris date
deq : float
Epoch of mean equinox of helio- and barycentric velocity output.
If `deq` is zero, `deq` is assumed to be equal to `dje`.
Returns
-------
dvelh : array
Heliocentric velocity vector [km/s].
dvelb : array
Barycentric velocity vector [km/s].
Notes
-----
.. note:: This function was ported from the IDL Astronomy User's Library.
:IDL - Documentation:
pro baryvel, dje, deq, dvelh, dvelb, JPL = JPL
NAME:
BARYVEL
PURPOSE:
Calculates heliocentric and barycentric velocity components of Earth.
EXPLANATION:
BARYVEL takes into account the Earth-Moon motion, and is useful for
radial velocity work to an accuracy of ~1 m/s.
CALLING SEQUENCE:
BARYVEL, dje, deq, dvelh, dvelb, [ JPL = ]
INPUTS:
DJE - (scalar) Julian ephemeris date.
DEQ - (scalar) epoch of mean equinox of dvelh and dvelb. If deq=0
then deq is assumed to be equal to dje.
OUTPUTS:
DVELH: (vector(3)) heliocentric velocity component. in km/s
DVELB: (vector(3)) barycentric velocity component. in km/s
The 3-vectors DVELH and DVELB are given in a right-handed coordinate
system with the +X axis toward the Vernal Equinox, and +Z axis
toward the celestial pole.
OPTIONAL KEYWORD SET:
JPL - if /JPL set, then BARYVEL will call the procedure JPLEPHINTERP
to compute the Earth velocity using the full JPL ephemeris.
The JPL ephemeris FITS file JPLEPH.405 must exist in either the
current directory, or in the directory specified by the
environment variable ASTRO_DATA. Alternatively, the JPL keyword
can be set to the full path and name of the ephemeris file.
A copy of the JPL ephemeris FITS file is available in
http://idlastro.gsfc.nasa.gov/ftp/data/
PROCEDURES CALLED:
Function PREMAT() -- computes precession matrix
JPLEPHREAD, JPLEPHINTERP, TDB2TDT - if /JPL keyword is set
NOTES:
Algorithm taken from FORTRAN program of Stumpff (1980, A&A Suppl, 41,1)
Stumpf claimed an accuracy of 42 cm/s for the velocity. A
comparison with the JPL FORTRAN planetary ephemeris program PLEPH
found agreement to within about 65 cm/s between 1986 and 1994
If /JPL is set (using JPLEPH.405 ephemeris file) then velocities are
given in the ICRS system; otherwise in the FK4 system.
EXAMPLE:
Compute the radial velocity of the Earth toward Altair on 15-Feb-1994
using both the original Stumpf algorithm and the JPL ephemeris
IDL> jdcnv, 1994, 2, 15, 0, jd ;==> JD = 2449398.5
IDL> baryvel, jd, 2000, vh, vb ;Original algorithm
==> vh = [-17.07243, -22.81121, -9.889315] ;Heliocentric km/s
==> vb = [-17.08083, -22.80471, -9.886582] ;Barycentric km/s
IDL> baryvel, jd, 2000, vh, vb, /jpl ;JPL ephemeris
==> vh = [-17.07236, -22.81126, -9.889419] ;Heliocentric km/s
==> vb = [-17.08083, -22.80484, -9.886409] ;Barycentric km/s
IDL> ra = ten(19,50,46.77)*15/!RADEG ;RA in radians
IDL> dec = ten(08,52,3.5)/!RADEG ;Dec in radians
IDL> v = vb[0]*cos(dec)*cos(ra) + $ ;Project velocity toward star
vb[1]*cos(dec)*sin(ra) + vb[2]*sin(dec)
REVISION HISTORY:
Jeff Valenti, U.C. Berkeley Translated BARVEL.FOR to IDL.
W. Landsman, Cleaned up program sent by Chris McCarthy (SfSU) June 1994
Converted to IDL V5.0 W. Landsman September 1997
Added /JPL keyword W. Landsman July 2001
Documentation update W. Landsman Dec 2005
"""
# Define constants
dc2pi = 2 * np.pi
cc2pi = 2 * np.pi
dc1 = 1.0
dcto = 2415020.0
dcjul = 36525.0 # days in Julian year
dcbes = 0.313
dctrop = 365.24219572 # days in tropical year (...572 insig)
dc1900 = 1900.0
AU = 1.4959787e8
# Constants dcfel(i,k) of fast changing elements.
dcfel = [1.7400353e00, 6.2833195099091e02, 5.2796e-6 \
,6.2565836e00, 6.2830194572674e02, -2.6180e-6 \
,4.7199666e00, 8.3997091449254e03, -1.9780e-5 \
,1.9636505e-1, 8.4334662911720e03, -5.6044e-5 \
,4.1547339e00, 5.2993466764997e01, 5.8845e-6 \
,4.6524223e00, 2.1354275911213e01, 5.6797e-6 \
,4.2620486e00, 7.5025342197656e00, 5.5317e-6 \
,1.4740694e00, 3.8377331909193e00, 5.6093e-6 ]
dcfel = np.resize(dcfel, (8,3))
# constants dceps and ccsel(i,k) of slowly changing elements.
dceps = [4.093198e-1, -2.271110e-4, -2.860401e-8 ]
ccsel = [1.675104e-2, -4.179579e-5, -1.260516e-7 \
,2.220221e-1, 2.809917e-2, 1.852532e-5 \
,1.589963e00, 3.418075e-2, 1.430200e-5 \
,2.994089e00, 2.590824e-2, 4.155840e-6 \
,8.155457e-1, 2.486352e-2, 6.836840e-6 \
,1.735614e00, 1.763719e-2, 6.370440e-6 \
,1.968564e00, 1.524020e-2, -2.517152e-6 \
,1.282417e00, 8.703393e-3, 2.289292e-5 \
,2.280820e00, 1.918010e-2, 4.484520e-6 \
,4.833473e-2, 1.641773e-4, -4.654200e-7 \
,5.589232e-2, -3.455092e-4, -7.388560e-7 \
,4.634443e-2, -2.658234e-5, 7.757000e-8 \
,8.997041e-3, 6.329728e-6, -1.939256e-9 \
,2.284178e-2, -9.941590e-5, 6.787400e-8 \
,4.350267e-2, -6.839749e-5, -2.714956e-7 \
,1.348204e-2, 1.091504e-5, 6.903760e-7 \
,3.106570e-2, -1.665665e-4, -1.590188e-7 ]
ccsel = np.resize(ccsel, (17,3))
# Constants of the arguments of the short-period perturbations.
dcargs = [5.0974222e0, -7.8604195454652e2 \
,3.9584962e0, -5.7533848094674e2 \
,1.6338070e0, -1.1506769618935e3 \
,2.5487111e0, -3.9302097727326e2 \
,4.9255514e0, -5.8849265665348e2 \
,1.3363463e0, -5.5076098609303e2 \
,1.6072053e0, -5.2237501616674e2 \
,1.3629480e0, -1.1790629318198e3 \
,5.5657014e0, -1.0977134971135e3 \
,5.0708205e0, -1.5774000881978e2 \
,3.9318944e0, 5.2963464780000e1 \
,4.8989497e0, 3.9809289073258e1 \
,1.3097446e0, 7.7540959633708e1 \
,3.5147141e0, 7.9618578146517e1 \
,3.5413158e0, -5.4868336758022e2 ]
dcargs = np.resize(dcargs, (15,2))
# Amplitudes ccamps(n,k) of the short-period perturbations.
ccamps = \
[-2.279594e-5, 1.407414e-5, 8.273188e-6, 1.340565e-5, -2.490817e-7 \
,-3.494537e-5, 2.860401e-7, 1.289448e-7, 1.627237e-5, -1.823138e-7 \
, 6.593466e-7, 1.322572e-5, 9.258695e-6, -4.674248e-7, -3.646275e-7 \
, 1.140767e-5, -2.049792e-5, -4.747930e-6, -2.638763e-6, -1.245408e-7 \
, 9.516893e-6, -2.748894e-6, -1.319381e-6, -4.549908e-6, -1.864821e-7 \
, 7.310990e-6, -1.924710e-6, -8.772849e-7, -3.334143e-6, -1.745256e-7 \
,-2.603449e-6, 7.359472e-6, 3.168357e-6, 1.119056e-6, -1.655307e-7 \
,-3.228859e-6, 1.308997e-7, 1.013137e-7, 2.403899e-6, -3.736225e-7 \
, 3.442177e-7, 2.671323e-6, 1.832858e-6, -2.394688e-7, -3.478444e-7 \
, 8.702406e-6, -8.421214e-6, -1.372341e-6, -1.455234e-6, -4.998479e-8 \
,-1.488378e-6, -1.251789e-5, 5.226868e-7, -2.049301e-7, 0.e0 \
,-8.043059e-6, -2.991300e-6, 1.473654e-7, -3.154542e-7, 0.e0 \
, 3.699128e-6, -3.316126e-6, 2.901257e-7, 3.407826e-7, 0.e0 \
, 2.550120e-6, -1.241123e-6, 9.901116e-8, 2.210482e-7, 0.e0 \
,-6.351059e-7, 2.341650e-6, 1.061492e-6, 2.878231e-7, 0.e0 ]
ccamps = np.resize(ccamps, (15,5))
# Constants csec3 and ccsec(n,k) of the secular perturbations in longitude.
ccsec3 = -7.757020e-8
ccsec = [1.289600e-6, 5.550147e-1, 2.076942e00 \
,3.102810e-5, 4.035027e00, 3.525565e-1 \
,9.124190e-6, 9.990265e-1, 2.622706e00 \
,9.793240e-7, 5.508259e00, 1.559103e01 ]
ccsec = np.resize(ccsec, (4,3))
# Sidereal rates.
dcsld = 1.990987e-7 # sidereal rate in longitude
ccsgd = 1.990969e-7 # sidereal rate in mean anomaly
# Constants used in the calculation of the lunar contribution.
cckm = 3.122140e-5
ccmld = 2.661699e-6
ccfdi = 2.399485e-7
# Constants dcargm(i,k) of the arguments of the perturbations of the motion
# of the moon.
dcargm = [5.1679830e0, 8.3286911095275e3 \
,5.4913150e0, -7.2140632838100e3 \
,5.9598530e0, 1.5542754389685e4 ]
dcargm = np.resize(dcargm, (3,2))
# Amplitudes ccampm(n,k) of the perturbations of the moon.
ccampm = [ 1.097594e-1, 2.896773e-7, 5.450474e-2, 1.438491e-7 \
,-2.223581e-2, 5.083103e-8, 1.002548e-2, -2.291823e-8 \
, 1.148966e-2, 5.658888e-8, 8.249439e-3, 4.063015e-8 ]
ccampm = np.resize(ccampm, (3,4))
# ccpamv(k)=a*m*dl,dt (planets), dc1mme=1-mass(earth+moon)
ccpamv = [8.326827e-11, 1.843484e-11, 1.988712e-12, 1.881276e-12]
dc1mme = 0.99999696e0
# Time arguments.
dt = (dje - dcto) / dcjul
tvec = np.array([1e0, dt, dt*dt])
# Values of all elements for the instant(aneous?) dje.
temp = idlMod(np.dot(dcfel, tvec), dc2pi)
dml = temp[0]
forbel = temp[1:8]
g = forbel[0] # old fortran equivalence
deps = idlMod(np.sum(tvec*dceps), dc2pi)
sorbel = idlMod(np.dot(ccsel, tvec), dc2pi)
e = sorbel[0] # old fortran equivalence
# Secular perturbations in longitude.
dummy = np.cos(2.0)
sn = np.sin(idlMod(np.dot(ccsec[::,1:3], tvec[0:2]), cc2pi))
# Periodic perturbations of the emb (earth-moon barycenter).
pertl = np.sum(ccsec[::,0] * sn) + (dt * ccsec3 * sn[2])
pertld = 0.0
pertr = 0.0
pertrd = 0.0
for k in xrange(15):
a = idlMod((dcargs[k,0] + dt*dcargs[k,1]), dc2pi)
cosa = np.cos(a)
sina = np.sin(a)
pertl = pertl + ccamps[k,0]*cosa + ccamps[k,1]*sina
pertr = pertr + ccamps[k,2]*cosa + ccamps[k,3]*sina
if k < 11:
pertld = pertld + (ccamps[k,1]*cosa-ccamps[k,0]*sina)*ccamps[k,4]
pertrd = pertrd + (ccamps[k,3]*cosa-ccamps[k,2]*sina)*ccamps[k,4]
# Elliptic part of the motion of the emb.
phi = (e*e/4e0)*(((8e0/e)-e)*np.sin(g) +5*np.sin(2*g) +(13/3e0)*e*np.sin(3*g))
f = g + phi
sinf = np.sin(f)
cosf = np.cos(f)
dpsi = (dc1 - e*e) / (dc1 + e*cosf)
phid = 2*e*ccsgd*((1 + 1.5*e*e)*cosf + e*(1.25 - 0.5*sinf*sinf))
psid = ccsgd*e*sinf / np.sqrt(dc1 - e*e)
# Perturbed heliocentric motion of the emb.
d1pdro = dc1+pertr
drd = d1pdro * (psid + dpsi*pertrd)
drld = d1pdro*dpsi * (dcsld+phid+pertld)
dtl = idlMod((dml + phi + pertl), dc2pi)
dsinls = np.sin(dtl)
dcosls = np.cos(dtl)
dxhd = drd*dcosls - drld*dsinls
dyhd = drd*dsinls + drld*dcosls
# Influence of eccentricity, evection and variation on the geocentric
# motion of the moon.
pertl = 0.0
pertld = 0.0
pertp = 0.0
pertpd = 0.0
for k in xrange(3):
a = idlMod((dcargm[k,0] + dt*dcargm[k,1]), dc2pi)
sina = np.sin(a)
cosa = np.cos(a)
pertl = pertl + ccampm[k,0]*sina
pertld = pertld + ccampm[k,1]*cosa
pertp = pertp + ccampm[k,2]*cosa
pertpd = pertpd - ccampm[k,3]*sina
# Heliocentric motion of the earth.
tl = forbel[1] + pertl
sinlm = np.sin(tl)
coslm = np.cos(tl)
sigma = cckm / (1.0 + pertp)
a = sigma*(ccmld + pertld)
b = sigma*pertpd
dxhd = dxhd + a*sinlm + b*coslm
dyhd = dyhd - a*coslm + b*sinlm
dzhd= -sigma*ccfdi*np.cos(forbel[2])
# Barycentric motion of the earth.
dxbd = dxhd*dc1mme
dybd = dyhd*dc1mme
dzbd = dzhd*dc1mme
for k in xrange(4):
plon = forbel[k+3]
pomg = sorbel[k+1]
pecc = sorbel[k+9]
tl = idlMod((plon + 2.0*pecc*np.sin(plon-pomg)), cc2pi)
dxbd = dxbd + ccpamv[k]*(np.sin(tl) + pecc*np.sin(pomg))
dybd = dybd - ccpamv[k]*(np.cos(tl) + pecc*np.cos(pomg))
dzbd = dzbd - ccpamv[k]*sorbel[k+13]*np.cos(plon - sorbel[k+5])
# Transition to mean equator of date.
dcosep = np.cos(deps)
dsinep = np.sin(deps)
dyahd = dcosep*dyhd - dsinep*dzhd
dzahd = dsinep*dyhd + dcosep*dzhd
dyabd = dcosep*dybd - dsinep*dzbd
dzabd = dsinep*dybd + dcosep*dzbd
# Epoch of mean equinox (deq) of zero implies that we should use
# Julian ephemeris date (dje) as epoch of mean equinox.
if deq == 0:
dvelh = AU * np.array([dxhd, dyahd, dzahd])
dvelb = AU * np.array([dxbd, dyabd, dzabd])
return dvelh, dvelb
# General precession from epoch dje to deq.
deqdat = (dje-dcto-dcbes) / dctrop + dc1900
prema = np.transpose(premat(deqdat, deq, FK4=True))
dvelh = AU * np.dot( [dxhd, dyahd, dzahd], prema )
dvelb = AU * np.dot( [dxbd, dyabd, dzabd], prema )
return dvelh, dvelb
def sunpos(jd, end_jd=None, jd_steps=None, outfile=None, radian=False, plot=False, full_output=False):
"""
Compute right ascension and declination of the Sun at a given time.
Parameters
----------
jd : float
The Julian date
end_jd : float, optional
The end of the time period as Julian date. If given,
`sunpos` computes RA and DEC at `jd_steps` time points
between `jd` and ending at `end_jd`.
jd_steps : integer, optional
The number of steps between `jd` and `end_jd`
for which RA and DEC are to be calculated.
outfile : string, optional
If given, the output will be written to a file named according
to `outfile`.
radian : boolean, optional
Results are returned in radian instead of in degrees.
Default is False.
plot : boolean, optional
If True, the result is plotted.
full_output: boolean, optional
If True, `sunpos`, additionally, returns the elongation and
obliquity of the Sun.
Returns
-------
Time : array
The JDs for which calculations where carried out.
Ra : array
Right ascension of the Sun.
Dec : array
Declination of the Sun.
Elongation : array, optional
Elongation of the Sun (only of `full_output`
is set to True).
Obliquity : array, optional
Obliquity of the Sun (only of `full_output`
is set to True).
Notes
-----
.. note:: This function was ported from the IDL Astronomy User's Library.
:IDL - Documentation:
NAME:
SUNPOS
PURPOSE:
To compute the RA and Dec of the Sun at a given date.
CALLING SEQUENCE:
SUNPOS, jd, ra, dec, [elong, obliquity, /RADIAN ]
INPUTS:
jd - The Julian date of the day (and time), scalar or vector
usually double precision
OUTPUTS:
ra - The right ascension of the sun at that date in DEGREES
double precision, same number of elements as jd
dec - The declination of the sun at that date in DEGREES
OPTIONAL OUTPUTS:
elong - Ecliptic longitude of the sun at that date in DEGREES.
obliquity - the obliquity of the ecliptic, in DEGREES
OPTIONAL INPUT KEYWORD:
/RADIAN - If this keyword is set and non-zero, then all output variables
are given in Radians rather than Degrees
NOTES:
Patrick Wallace (Rutherford Appleton Laboratory, UK) has tested the
accuracy of a C adaptation of the sunpos.pro code and found the
following results. From 1900-2100 SUNPOS gave 7.3 arcsec maximum
error, 2.6 arcsec RMS. Over the shorter interval 1950-2050 the figures
were 6.4 arcsec max, 2.2 arcsec RMS.
The returned RA and Dec are in the given date's equinox.
Procedure was extensively revised in May 1996, and the new calling
sequence is incompatible with the old one.
METHOD:
Uses a truncated version of Newcomb's Sun. Adapted from the IDL
routine SUN_POS by CD Pike, which was adapted from a FORTRAN routine
by B. Emerson (RGO).
EXAMPLE:
(1) Find the apparent RA and Dec of the Sun on May 1, 1982
IDL> jdcnv, 1982, 5, 1,0 ,jd ;Find Julian date jd = 2445090.5
IDL> sunpos, jd, ra, dec
IDL> print,adstring(ra,dec,2)
02 31 32.61 +14 54 34.9
The Astronomical Almanac gives 02 31 32.58 +14 54 34.9 so the error
in SUNPOS for this case is < 0.5".
(2) Find the apparent RA and Dec of the Sun for every day in 1997
IDL> jdcnv, 1997,1,1,0, jd ;Julian date on Jan 1, 1997
IDL> sunpos, jd+ dindgen(365), ra, dec ;RA and Dec for each day
MODIFICATION HISTORY:
Written by Michael R. Greason, STX, 28 October 1988.
Accept vector arguments, W. Landsman April,1989
Eliminated negative right ascensions. MRG, Hughes STX, 6 May 1992.
Rewritten using the 1993 Almanac. Keywords added. MRG, HSTX,
10 February 1994.
Major rewrite, improved accuracy, always return values in degrees
W. Landsman May, 1996
Added /RADIAN keyword, W. Landsman August, 1997
Converted to IDL V5.0 W. Landsman September 1997
"""
if end_jd is None:
# Form time in Julian centuries from 1900.0
start_jd = (jd - 2415020.0)/36525.0
# Zime array
time = np.array([start_jd])
else:
if jd >= end_jd:
raise(PE.PyAValError("`end_jd` needs to be larger than `jd`.", \
where="sunpos", \
solution="Modify the parameters."))
if jd_steps is None:
raise(PE.PyAValError("You specified `end_jd`, but no value for `jd_steps`.", \
where="sunpos", \
solution="Specify `jd_steps`, e.g., given jd_steps=10"))
# Form time in Julian centuries from 1900.0
start_jd = (jd - 2415020.0)/36525.0
end_jd = (end_jd - 2415020.0)/36525.0
# Time array
timestep = (end_jd-start_jd)/float(jd_steps)
time = np.arange(start_jd, end_jd, timestep)
# Mean solar longitude
sunlon = (279.696678 + idlMod( (36000.768925*time), 360.0) )*3600.0
# Allow for ellipticity of the orbit (equation of center)
# using the Earth's mean anomaly ME
me = 358.475844 + idlMod( (35999.049750*time) , 360.0 )
ellcor = ( 6910.1 - 17.2*time ) * np.sin(me*np.pi/180.) + 72.3 * np.sin(2.0*me*np.pi/180.)
sunlon += ellcor
# Allow for the Venus perturbations using the mean anomaly of Venus MV
mv = 212.603219 + idlMod( (58517.803875*time) , 360.0 )
vencorr = 4.8 * np.cos( (299.1017 + mv - me)*np.pi/180. ) + \
5.5 * np.cos( (148.3133 + 2.0 * mv - 2.0 * me )*np.pi/180. ) + \
2.5 * np.cos( (315.9433 + 2.0 * mv - 3.0 * me )*np.pi/180. ) + \
1.6 * np.cos( (345.2533 + 3.0 * mv - 4.0 * me )*np.pi/180. ) + \
1.0 * np.cos( (318.15 + 3.0 * mv - 5.0 * me )*np.pi/180. )
sunlon += vencorr
# Allow for the Mars perturbations using the mean anomaly of Mars MM
mm = 319.529425 + idlMod( (19139.858500*time) , 360.0 )
marscorr = 2.0 * np.cos( (343.8883 - 2.0 * mm + 2.0 * me)*np.pi/180. ) + \
1.8 * np.cos( (200.4017 - 2.0 * mm + me)*np.pi/180. )
sunlon += marscorr
# Allow for the Jupiter perturbations using the mean anomaly of Jupiter MJ
mj = 225.328328 + idlMod( (3034.6920239*time) , 360.0 )
jupcorr = 7.2 * np.cos( (179.5317 - mj + me )*np.pi/180. ) + \
2.6 * np.cos( (263.2167 - mj )*np.pi/180. ) + \
2.7 * np.cos( ( 87.1450 - 2.0 * mj + 2.0 * me )*np.pi/180. ) + \
1.6 * np.cos( (109.4933 - 2.0 * mj + me )*np.pi/180. )
sunlon += jupcorr
# Allow for the Moon's perturbations using the mean elongation of
# the Moon from the Sun D
d = 350.7376814 + idlMod( (445267.11422*time) , 360.0 )
mooncorr = 6.5*np.sin(d*np.pi/180.)
sunlon += mooncorr
# Allow for long period terms
longterm = 6.4*np.sin( (231.19 + 20.20*time)*np.pi/180. )
sunlon += longterm
sunlon = idlMod( ( sunlon + 2592000.0 ) , 1296000.0 )
longmed = sunlon/3600.0
# Allow for Aberration
sunlon -= 20.5
# Allow for Nutation using the longitude of the Moons mean node OMEGA
omega = 259.183275 - idlMod( (1934.142008*time) , 360.0 )
sunlon = sunlon - 17.2*np.sin(omega*np.pi/180.)
# Calculate the True Obliquity
oblt = 23.452294 - 0.0130125*time + ( 9.2*np.cos(omega*np.pi/180.) )/3600.0
# Right Ascension and Declination
sunlon /= 3600.0
ra = np.arctan2( np.sin(sunlon*np.pi/180.) * np.cos(oblt*np.pi/180.), np.cos(sunlon*np.pi/180.) )
neg = np.where(ra < 0.0)[0]
nneg = len(neg)
if nneg > 0: ra[neg] += 2.0*np.pi
dec = np.arcsin( np.sin(sunlon*np.pi/180.) * np.sin(oblt*np.pi/180.) )
if radian:
oblt *= (np.pi/180.)
longmed *= (np.pi/180.)
else:
ra /= (np.pi/180.)
dec /= (np.pi/180.)
jd = time*36525.0 + 2415020.0
if outfile is not None:
# Write results to a file
of = open(outfile, 'w')
of.write("# File created by 'sunpos'\n")
if not full_output:
of.write("# 1) JD, 2) ra, 3) dec\n")
np.savetxt(of, np.transpose(np.vstack((jd, ra, dec))))
else:
of.write("# 1) JD, 2) ra, 3) dec, 4) longitude, 5) obliquity\n")
np.savetxt(of, np.transpose(np.vstack((jd, ra, dec, longmed, oblt))))
of.close()
if plot:
if not _ic.check["matplotlib"]:
raise(PE.PyARequiredImport("Could not import matplotlib.", \
where="sunpos", \
solution=["Install matplotlib", "Switch `plot` flag to False."]))
import matplotlib.pylab as plt
plt.plot(jd, ra, 'k-', label="RA")
plt.plot(jd, dec, 'g-', label="DEC")
plt.legend()
plt.show()
if full_output:
return jd, ra, dec, longmed, oblt
else:
return jd, ra, dec
