Table of contents
CSPICE_LSPCN computes L_s, the planetocentric longitude of the sun,
as seen from a specified body.
Given:
body the name of the central body, typically a planet.
[1,c1] = size(body); char = class(body)
or
[1,1] = size(body); cell = class(body)
et the epoch(s) at which the longitude of the sun (L_s) is
to be computed. `et' is expressed as seconds past J2000
TDB (Barycentric Dynamical Time).
[1,n] = size(et); double = class(et)
abcorr indicates the aberration corrections to be applied
when computing the longitude of the sun.
[1,c2] = size(abcorr); char = class(abcorr)
or
[1,1] = size(abcorr); cell = class(abcorr)
`abcorr' may be any of the following.
'NONE' Apply no correction.
'LT' Correct the position of the sun,
relative to the central body, for
planetary (light time) aberration.
'LT+S' Correct the position of the sun,
relative to the central body, for
planetary and stellar aberrations.
the call:
[lspcn] = cspice_lspcn( body, et, abcorr )
returns:
lspcn the planetocentric longitude(s) of the sun, often called
"L_s," for the specified body at the specified time.
[1,n] = size(et); double = class(et)
The longitude is defined in a right-handed frame whose
basis vectors are defined as follows:
- The positive Z direction is given by the instantaneous
angular velocity vector of the orbit of the body about
the sun.
- The positive X direction is that of the cross product
of the instantaneous north spin axis of the body with
the positive Z direction.
- The positive Y direction is Z x X.
Units are radians; the range is 0 to 2*pi. Longitudes are
positive to the east.
`lspcn' returns with the same vectorization measure (N) as
`et'.
None.
Any numerical results shown for these examples may differ between
platforms as the results depend on the SPICE kernels used as input
and the machine specific arithmetic implementation.
1) Compute the planetocentric longitude of the Sun as seen from
the Earth on 21 March 2006. The result should be approximately
0, as the date corresponds to the Spring equinox.
Use the meta-kernel shown below to load the required SPICE
kernels.
KPL/MK
File name: lspcn_ex1.tm
This meta-kernel is intended to support operation of SPICE
example programs. The kernels shown here should not be
assumed to contain adequate or correct versions of data
required by SPICE-based user applications.
In order for an application to use this meta-kernel, the
kernels referenced here must be present in the user's
current working directory.
The names and contents of the kernels referenced
by this meta-kernel are as follows:
File name Contents
--------- --------
de421.bsp Planetary ephemeris
pck00010.tpc Planet orientation and
radii
naif0011.tls Leapseconds
\begindata
KERNELS_TO_LOAD = ( 'de421.bsp',
'pck00010.tpc',
'naif0011.tls' )
\begintext
End of meta-kernel
Example code begins here.
function lspcn_ex1()
%
% Load kernels.
%
cspice_furnsh( 'lspcn_ex1.tm' )
et = cspice_str2et('21 march 2006');
lspcn = cspice_lspcn( 'earth', et, 'none' ) * cspice_dpr;
disp( lspcn )
%
% It's always good form to unload kernels after use,
% particularly in Matlab due to data persistence.
%
cspice_kclear
When this program was executed on a Mac/Intel/Octave6.x/64-bit
platform, the output was:
0.23645
2) Compute the planetocentric longitude of the Sun as seen from
the Earth for a set of dates.
Use the meta-kernel from the first example load the required SPICE
kernels.
Example code begins here.
function lspcn_ex2()
%
% Load kernels.
%
cspice_furnsh( 'lspcn_ex1.tm' )
et = cspice_str2et('21 march 2005') + [0:1000000.:10000000.];
lspcn = cspice_lspcn( 'earth', et, 'none' ) * cspice_dpr;
utcstr = cspice_et2utc(et, 'C', 0);
disp( ' UTC time lspcn' )
disp( '-------------------- --------')
for i = 1:11
fprintf( '%s %8.4f\n', utcstr(i,:), lspcn(i) )
end
%
% It's always good form to unload kernels after use,
% particularly in Matlab due to data persistence.
%
cspice_kclear
When this program was executed on a Mac/Intel/Octave6.x/64-bit
platform, the output was:
UTC time lspcn
-------------------- --------
2005 MAR 21 00:00:00 0.4815
2005 APR 01 13:46:40 11.9353
2005 APR 13 03:33:20 23.3193
2005 APR 24 17:20:00 34.6294
2005 MAY 06 07:06:40 45.8611
2005 MAY 17 20:53:20 57.0476
2005 MAY 29 10:40:00 68.1626
2005 JUN 10 00:26:40 79.2509
2005 JUN 21 14:13:20 90.3058
2005 JUL 03 04:00:00 101.3366
2005 JUL 14 17:46:40 112.3833
The direction of the vernal equinox for the central body is
determined from the instantaneous equatorial and orbital planes
of the central body. This equinox definition is specified in
reference [1]. The "instantaneous orbital plane" is interpreted
in this routine as the plane normal to the cross product of the
position and velocity of the central body relative to the sun.
The geometric state of the central body relative to the sun is
used for this normal vector computation. The "instantaneous
equatorial plane" is normal to the central body's north pole
at the requested epoch. The pole direction is determined from
rotational elements loaded via a PCK file.
The result returned by this routine will depend on the
ephemeris data and rotational elements used. The result may
differ from that given in any particular version of the
Astronomical Almanac, due to differences in these input data,
and due to differences in precision of the computations.
1) If the input body name cannot be translated to an ID code,
and if the name is not a string representation of an integer
(for example, '399'), the error SPICE(NOTRANSLATION) is
signaled by a routine in the call tree of this routine.
2) If no SPK (ephemeris) file has been loaded prior to calling
this routine, or if the SPK data has insufficient coverage, an
error is signaled by a routine in the call tree of this
routine.
3) If a PCK file containing rotational elements for the central
body has not been loaded prior to calling this routine, an
error is signaled by a routine in the call tree of this
routine.
4) If the instantaneous angular velocity and spin axis of `body'
are parallel, an error is signaled by a
routine in the call tree of this routine.
5) If any of the input arguments, `body', `et' or `abcorr', is
undefined, an error is signaled by the Matlab error handling
system.
6) If any of the input arguments, `body', `et' or `abcorr', is
not of the expected type, or it does not have the expected
dimensions and size, an error is signaled by the Mice
interface.
Appropriate SPICE kernels must be loaded by the calling program
before this routine is called.
The following data are required:
- An SPK file (or files) containing ephemeris data sufficient to
compute the geometric state of the central body relative to
the sun at `et' must be loaded before this routine is called. If
light time correction is used, data must be available that
enable computation of the state the sun relative to the solar
system barycenter at the light-time corrected epoch. If
stellar aberration correction is used, data must be available
that enable computation of the state the central body relative
to the solar system barycenter at `et'.
- A PCK file containing rotational elements for the central body
must be loaded before this routine is called.
None.
MICE.REQ
ABCORR.REQ
[1] "The Astronomical Almanac for the Year 2005," page L9,
United States Naval Observatory, U.S. Government Printing
Office, Washington, D.C., 2004.
J. Diaz del Rio (ODC Space)
E.D. Wright (JPL)
-Mice Version 1.1.0, 25-AUG-2021 (EDW) (JDR)
Edited the header to comply with NAIF standard. Added
meta-kernel to example #1. Updated code examples to produce
formatted output and added a call to cspice_kclear. Added the
problem statement to both examples.
Added -Parameters, -Particulars, -Exceptions, -Files, -Restrictions,
-Literature_References and -Author_and_Institution sections, and
square brackets to output argument in function declaration.
Eliminated use of "lasterror" in rethrow.
Removed reference to the function's corresponding CSPICE header from
-Required_Reading section.
-Mice Version 1.0.0, 10-NOV-2015 (EDW)
Script rewritten to call CSPICE interface.
-Mice Version 0.9.0, 23-OCT-2015 (EDW)
Pure Matlab script.
planetocentric longitude of sun
compute L_s
compute Ls
compute L_sub_s
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