# Seeking an ecliptic monitor

1. Jan 30, 2014

### snoopies622

I'm looking for a good source for the day by day (or even smaller graduations would be nice) angle of the sun along the ecliptic. I would like to know exactly when the various "solar terms" begin and end, and their dates and times vary from year to year.

http://en.wikipedia.org/wiki/Solar_term

Thanks.

2. Jan 30, 2014

### phyzguy

The JPL Horizons database will give you this information. For example, I set it up as follows:

Ephemeris Type [change] : OBSERVER
Target Body [change] : Sun [Sol] [10]
Observer Location [change] : Geocentric [500]
Time Span [change] : Start=2014-03-20 21:00, Stop=2014-03-20 22:00, Step=1 m
Table Settings [change] : QUANTITIES=1,9,15,20,23,24
Display/Output [change] : default (formatted HTML)

And I got the output below. This allows you to see that the vernal equinox (Sun's longitude = 0) happens at 2014-Mar-20 21:40 . It's a simple matter to set it up to find whatever longitude you want. For example, the first one (longitude = 315 degrees, which is RA = 21h) happens at 2014-Feb-01 16:23

Code (Text):

*******************************************************************************
Ephemeris / WWW_USER Thu Jan 30 07:11:50 2014 Pasadena, USA      / Horizons
*******************************************************************************
Target body name: Sun (10)                        {source: DE-0431LE-0431}
Center body name: Earth (399)                     {source: DE-0431LE-0431}
Center-site name: GEOCENTRIC
*******************************************************************************
Start time      : A.D. 2014-Mar-20 21:00:00.0000 UT
Stop  time      : A.D. 2014-Mar-20 22:00:00.0000 UT
Step-size       : 1 minutes
*******************************************************************************
Target pole/equ : IAU_SUN                         {East-longitude +}
Target radii    : 696000.0 x 696000.0 x 696000.0 k{Equator, meridian, pole}
Center geodetic : 0.00000000,0.00000000,0.0000000 {E-lon(deg),Lat(deg),Alt(km)}
Center cylindric: 0.00000000,0.00000000,0.0000000 {E-lon(deg),Dxy(km),Dz(km)}
Center pole/equ : High-precision EOP model        {East-longitude +}
Center radii    : 6378.1 x 6378.1 x 6356.8 km     {Equator, meridian, pole}
Target primary  : Sun
Vis. interferer : MOON (R_eq= 1737.400) km        {source: DE-0431LE-0431}
Rel. light bend : Sun, EARTH                      {source: DE-0431LE-0431}
Rel. lght bnd GM: 1.3271E+11, 3.9860E+05 km^3/s^2
Atmos refraction: NO (AIRLESS)
RA format       : HMS
Time format     : CAL
EOP file        : eop.140129.p140422
EOP coverage    : DATA-BASED 1962-JAN-20 TO 2014-JAN-29. PREDICTS-> 2014-APR-21
Units conversion: 1 au= 149597870.700 km, c= 299792.458 km/s, 1 day= 86400.0 s
Table cut-offs 1: Elevation (-90.0deg=NO ),Airmass (>38.000=NO), Daylight (NO )
Table cut-offs 2: Solar Elongation (  0.0,180.0=NO ),Local Hour Angle( 0.0=NO )
****************************************************************************************************************************
Date__(UT)__HR:MN     R.A._(ICRF/J2000.0)_DEC  APmag  S-brt Sl-lon Sl-lat            delta      deldot    S-O-T /r    S-T-O
****************************************************************************************************************************
$$SOE 2014-Mar-20 21:00 23 59 53.90 -00 00 40.0 -26.75 -10.59 n.a. n.a. 0.99596242291714 0.4932997 0.0000 /? 0.0000 2014-Mar-20 21:01 23 59 54.05 -00 00 39.1 -26.75 -10.59 n.a. n.a. 0.99596262076792 0.4933022 0.0000 /? 0.0000 2014-Mar-20 21:02 23 59 54.20 -00 00 38.1 -26.75 -10.59 n.a. n.a. 0.99596281861970 0.4933046 0.0000 /? 0.0000 2014-Mar-20 21:03 23 59 54.35 -00 00 37.1 -26.75 -10.59 n.a. n.a. 0.99596301647246 0.4933071 0.0000 /? 0.0000 2014-Mar-20 21:04 23 59 54.51 -00 00 36.1 -26.75 -10.59 n.a. n.a. 0.99596321432621 0.4933096 0.0000 /? 0.0000 2014-Mar-20 21:05 23 59 54.66 -00 00 35.1 -26.75 -10.59 n.a. n.a. 0.99596341218094 0.4933120 0.0000 /? 0.0000 2014-Mar-20 21:06 23 59 54.81 -00 00 34.1 -26.75 -10.59 n.a. n.a. 0.99596361003666 0.4933145 0.0000 /? 0.0000 2014-Mar-20 21:07 23 59 54.96 -00 00 33.1 -26.75 -10.59 n.a. n.a. 0.99596380789337 0.4933170 0.0000 /? 0.0000 2014-Mar-20 21:08 23 59 55.11 -00 00 32.1 -26.75 -10.59 n.a. n.a. 0.99596400575107 0.4933194 0.0000 /? 0.0000 2014-Mar-20 21:09 23 59 55.27 -00 00 31.2 -26.75 -10.59 n.a. n.a. 0.99596420360975 0.4933219 0.0000 /? 0.0000 2014-Mar-20 21:10 23 59 55.42 -00 00 30.2 -26.75 -10.59 n.a. n.a. 0.99596440146942 0.4933243 0.0000 /? 0.0000 2014-Mar-20 21:11 23 59 55.57 -00 00 29.2 -26.75 -10.59 n.a. n.a. 0.99596459933007 0.4933268 0.0000 /? 0.0000 2014-Mar-20 21:12 23 59 55.72 -00 00 28.2 -26.75 -10.59 n.a. n.a. 0.99596479719171 0.4933292 0.0000 /? 0.0000 2014-Mar-20 21:13 23 59 55.87 -00 00 27.2 -26.75 -10.59 n.a. n.a. 0.99596499505434 0.4933317 0.0000 /? 0.0000 2014-Mar-20 21:14 23 59 56.02 -00 00 26.2 -26.75 -10.59 n.a. n.a. 0.99596519291795 0.4933342 0.0000 /? 0.0000 2014-Mar-20 21:15 23 59 56.18 -00 00 25.2 -26.75 -10.59 n.a. n.a. 0.99596539078255 0.4933366 0.0000 /? 0.0000 2014-Mar-20 21:16 23 59 56.33 -00 00 24.2 -26.75 -10.59 n.a. n.a. 0.99596558864814 0.4933391 0.0000 /? 0.0000 2014-Mar-20 21:17 23 59 56.48 -00 00 23.3 -26.75 -10.59 n.a. n.a. 0.99596578651471 0.4933415 0.0000 /? 0.0000 2014-Mar-20 21:18 23 59 56.63 -00 00 22.3 -26.75 -10.59 n.a. n.a. 0.99596598438226 0.4933440 0.0000 /? 0.0000 2014-Mar-20 21:19 23 59 56.78 -00 00 21.3 -26.75 -10.59 n.a. n.a. 0.99596618225081 0.4933465 0.0000 /? 0.0000 2014-Mar-20 21:20 23 59 56.94 -00 00 20.3 -26.75 -10.59 n.a. n.a. 0.99596638012033 0.4933489 0.0000 /? 0.0000 2014-Mar-20 21:21 23 59 57.09 -00 00 19.3 -26.75 -10.59 n.a. n.a. 0.99596657799084 0.4933514 0.0000 /? 0.0000 2014-Mar-20 21:22 23 59 57.24 -00 00 18.3 -26.75 -10.59 n.a. n.a. 0.99596677586234 0.4933538 0.0000 /? 0.0000 2014-Mar-20 21:23 23 59 57.39 -00 00 17.3 -26.75 -10.59 n.a. n.a. 0.99596697373483 0.4933563 0.0000 /? 0.0000 2014-Mar-20 21:24 23 59 57.54 -00 00 16.3 -26.75 -10.59 n.a. n.a. 0.99596717160829 0.4933587 0.0000 /? 0.0000 2014-Mar-20 21:25 23 59 57.70 -00 00 15.4 -26.75 -10.59 n.a. n.a. 0.99596736948275 0.4933612 0.0000 /? 0.0000 2014-Mar-20 21:26 23 59 57.85 -00 00 14.4 -26.75 -10.59 n.a. n.a. 0.99596756735818 0.4933636 0.0000 /? 0.0000 2014-Mar-20 21:27 23 59 58.00 -00 00 13.4 -26.75 -10.59 n.a. n.a. 0.99596776523460 0.4933661 0.0000 /? 0.0000 2014-Mar-20 21:28 23 59 58.15 -00 00 12.4 -26.75 -10.59 n.a. n.a. 0.99596796311201 0.4933686 0.0000 /? 0.0000 2014-Mar-20 21:29 23 59 58.30 -00 00 11.4 -26.75 -10.59 n.a. n.a. 0.99596816099040 0.4933710 0.0000 /? 0.0000 2014-Mar-20 21:30 23 59 58.45 -00 00 10.4 -26.75 -10.59 n.a. n.a. 0.99596835886978 0.4933735 0.0000 /? 0.0000 2014-Mar-20 21:31 23 59 58.61 -00 00 09.4 -26.75 -10.59 n.a. n.a. 0.99596855675014 0.4933759 0.0000 /? 0.0000 2014-Mar-20 21:32 23 59 58.76 -00 00 08.4 -26.75 -10.59 n.a. n.a. 0.99596875463148 0.4933784 0.0000 /? 0.0000 2014-Mar-20 21:33 23 59 58.91 -00 00 07.4 -26.75 -10.59 n.a. n.a. 0.99596895251381 0.4933808 0.0000 /? 0.0000 2014-Mar-20 21:34 23 59 59.06 -00 00 06.5 -26.75 -10.59 n.a. n.a. 0.99596915039712 0.4933833 0.0000 /? 0.0000 2014-Mar-20 21:35 23 59 59.21 -00 00 05.5 -26.75 -10.59 n.a. n.a. 0.99596934828142 0.4933857 0.0000 /? 0.0000 2014-Mar-20 21:36 23 59 59.37 -00 00 04.5 -26.75 -10.59 n.a. n.a. 0.99596954616670 0.4933882 0.0000 /? 0.0000 2014-Mar-20 21:37 23 59 59.52 -00 00 03.5 -26.75 -10.59 n.a. n.a. 0.99596974405296 0.4933906 0.0000 /? 0.0000 2014-Mar-20 21:38 23 59 59.67 -00 00 02.5 -26.75 -10.59 n.a. n.a. 0.99596994194021 0.4933931 0.0000 /? 0.0000 2014-Mar-20 21:39 23 59 59.82 -00 00 01.5 -26.75 -10.59 n.a. n.a. 0.99597013982844 0.4933955 0.0000 /? 0.0000 2014-Mar-20 21:40 23 59 59.97 -00 00 00.5 -26.75 -10.59 n.a. n.a. 0.99597033771766 0.4933980 0.0000 /? 0.0000 2014-Mar-20 21:41 00 00 00.12 +00 00 00.5 -26.75 -10.59 n.a. n.a. 0.99597053560786 0.4934004 0.0000 /? 0.0000 2014-Mar-20 21:42 00 00 00.28 +00 00 01.4 -26.75 -10.59 n.a. n.a. 0.99597073349904 0.4934029 0.0000 /? 0.0000 2014-Mar-20 21:43 00 00 00.43 +00 00 02.4 -26.75 -10.59 n.a. n.a. 0.99597093139120 0.4934053 0.0000 /? 0.0000 2014-Mar-20 21:44 00 00 00.58 +00 00 03.4 -26.75 -10.59 n.a. n.a. 0.99597112928435 0.4934078 0.0000 /? 0.0000 2014-Mar-20 21:45 00 00 00.73 +00 00 04.4 -26.75 -10.59 n.a. n.a. 0.99597132717848 0.4934102 0.0000 /? 0.0000 2014-Mar-20 21:46 00 00 00.88 +00 00 05.4 -26.75 -10.59 n.a. n.a. 0.99597152507359 0.4934127 0.0000 /? 0.0000 2014-Mar-20 21:47 00 00 01.04 +00 00 06.4 -26.75 -10.59 n.a. n.a. 0.99597172296969 0.4934151 0.0000 /? 0.0000 2014-Mar-20 21:48 00 00 01.19 +00 00 07.4 -26.75 -10.59 n.a. n.a. 0.99597192086676 0.4934176 0.0000 /? 0.0000 2014-Mar-20 21:49 00 00 01.34 +00 00 08.4 -26.75 -10.59 n.a. n.a. 0.99597211876483 0.4934200 0.0000 /? 0.0000 2014-Mar-20 21:50 00 00 01.49 +00 00 09.3 -26.75 -10.59 n.a. n.a. 0.99597231666387 0.4934225 0.0000 /? 0.0000 2014-Mar-20 21:51 00 00 01.64 +00 00 10.3 -26.75 -10.59 n.a. n.a. 0.99597251456389 0.4934249 0.0000 /? 0.0000 2014-Mar-20 21:52 00 00 01.80 +00 00 11.3 -26.75 -10.59 n.a. n.a. 0.99597271246490 0.4934274 0.0000 /? 0.0000 2014-Mar-20 21:53 00 00 01.95 +00 00 12.3 -26.75 -10.59 n.a. n.a. 0.99597291036689 0.4934298 0.0000 /? 0.0000 2014-Mar-20 21:54 00 00 02.10 +00 00 13.3 -26.75 -10.59 n.a. n.a. 0.99597310826986 0.4934323 0.0000 /? 0.0000 2014-Mar-20 21:55 00 00 02.25 +00 00 14.3 -26.75 -10.59 n.a. n.a. 0.99597330617382 0.4934347 0.0000 /? 0.0000 2014-Mar-20 21:56 00 00 02.40 +00 00 15.3 -26.75 -10.59 n.a. n.a. 0.99597350407875 0.4934372 0.0000 /? 0.0000 2014-Mar-20 21:57 00 00 02.55 +00 00 16.3 -26.75 -10.59 n.a. n.a. 0.99597370198467 0.4934396 0.0000 /? 0.0000 2014-Mar-20 21:58 00 00 02.71 +00 00 17.2 -26.75 -10.59 n.a. n.a. 0.99597389989157 0.4934421 0.0000 /? 0.0000 2014-Mar-20 21:59 00 00 02.86 +00 00 18.2 -26.75 -10.59 n.a. n.a. 0.99597409779945 0.4934445 0.0000 /? 0.0000 2014-Mar-20 22:00 00 00 03.01 +00 00 19.2 -26.75 -10.59 n.a. n.a. 0.99597429570831 0.4934470 0.0000 /? 0.0000$$EOE
****************************************************************************************************************************
Column meaning:

TIME

Prior to 1962, times are UT1. Dates thereafter are UTC. Any 'b' symbol in
the 1st-column denotes a B.C. date. First-column blank (" ") denotes an A.D.
date. Calendar dates prior to 1582-Oct-15 are in the Julian calendar system.
Later calendar dates are in the Gregorian system.

Time tags refer to the same instant throughout the universe, regardless of
where the observer is located.

The dynamical Coordinate Time scale is used internally. It is equivalent to
the current IAU definition of "TDB". Conversion between CT and the selected
non-uniform UT output scale has not been determined for UTC times after the
next July or January 1st.  The last known leap-second is used over any future
interval.

NOTE: "n.a." in output means quantity "not available" at the print-time.

R.A._(ICRF/J2000.0)_DEC =
J2000.0 astrometric right ascension and declination of target center.
Adjusted for light-time. Units: HMS (HH MM SS.ff) and DMS (DD MM SS.f)

APmag S-brt =
Sun's approximate apparent visual magnitude & surface brightness.
APmag= M - 5 + 5*log10(d), where M= 4.83 and d= distance from Sun in parsecs.
Units: MAGNITUDE & VISUAL MAGNITUDES PER SQUARE ARCSECOND

Sl-lon Sl-lat =
Apparent planetographic ("geodetic") longitude and latitude of the Sun
(IAU2009) as seen by the observer at print-time. This is NOT exactly the same
as the "sub-solar" (nearest) point for a non-spherical target shape, but is
generally very close if not an irregular body shape. Light travel-time from Sun
to target and from target to observer is taken into account. Latitude is the
angle between the equatorial plane and the line perpendicular to the reference
ellipsoid of the body. The reference ellipsoid is an oblate spheroid with a
single flatness coefficient in which the y-axis body radius is taken to be the
same value as the x-axis radius.  For the gas giants Jupiter, Saturn, Uranus
and Neptune, IAU2009 longitude is based on the "System III" prime meridian
rotation angle of the magnetic field. By contrast, pole direction (thus
latitude) is relative to the body dynamical equator. There can be an offset
between the magnetic pole and the dynamical pole of rotation. Positive
longitude is to the EAST.  Units: DEGREES

delta  deldot =
Range ("delta") and range-rate ("delta-dot") of target center with respect
to the observer at the instant light seen by the observer at print-time would
have left the target center (print-time minus down-leg light-time); the
distance traveled by a light ray emanating from the center of the target and
recorded by the observer at print-time. "deldot" is a projection of the
velocity vector along this ray, the light-time-corrected line-of-sight from the
coordinate center, and indicates relative motion. A positive "deldot" means the
target center is moving away from the observer (coordinate center). A negative
"deldot" means the target center is moving toward the observer.
Units: AU and KM/S

S-O-T /r =
Sun-Observer-Target angle; target's apparent solar elongation seen from
observer location at print-time. If negative, the target center is behind
the Sun. Angular units: DEGREES.

The '/r' column is a Sun-relative code, output for observing sites
with defined rotation models only.

/T indicates target trails Sun (evening sky)
/L indicates target leads Sun  (morning sky)

NOTE: The S-O-T solar elongation angle is the total separation in any
direction. It does not indicate the angle of Sun leading or trailing.

S-T-O =
"S-T-O" is the Sun->Target->Observer angle; the interior vertex angle at
target center formed by a vector to the apparent center of the Sun at
reflection time on the target and the apparent vector to the observer at
print-time. Slightly different from true PHASE ANGLE (requestable separately)
at the few arcsecond level in that it includes stellar aberration on the
down-leg from target to observer.  Units: DEGREES

Computations by ...
Solar System Dynamics Group, Horizons On-Line Ephemeris System
4800 Oak Grove Drive, Jet Propulsion Laboratory
Information: http://ssd.jpl.nasa.gov/
Connect    : telnet://ssd.jpl.nasa.gov:6775  (via browser)
telnet ssd.jpl.nasa.gov 6775    (via command-line)
Author     : Jon.Giorgini@jpl.nasa.gov

****************************************************************************************************************************

3. Jan 30, 2014

### snoopies622

Thanks phyzguy, that was easy. :) If I used it correctly, this year solar spring begins Feburary 1st, 11:23 AM EST. Yay spring!

4. Jan 30, 2014

### snoopies622

On the other hand, sites like this one point to a later date — even after compensating for the different time zone.

http://www.asia-home.com/china/solterms/lang/en/print/dyna.php [Broken]

Would someone please confirm my prediction?

Last edited by a moderator: May 6, 2017
5. Jan 30, 2014

### phyzguy

I think you did it right. I don't know what causes the discrepancy. I would tend to believe JPL.

6. Jan 30, 2014

### tfr000

What ya doing with the data? Anything fun?

I went to http://www.imcce.fr/en/ephemerides/formulaire/form_ephepos.php and typed in your data... are you looking for the time when the Sun's ecliptic longitude is exactly 21h00m?
I got about 11:44 UTC on Feb. 1, which is 7:44 Eastern, I believe.

Edit... oops, make that the Sun's right ascention is exactly 21h00m.

Last edited: Jan 30, 2014
7. Jan 30, 2014

### snoopies622

Thanks for the other source tfr000, I got the same answer. Yup, 21 hours exactly ~ I just wanna know when to celebrate spring!

8. Jan 30, 2014

### davenn

when the daffodils bloom and the lambs are frolicking in the fields

Dave