A personal blog by George Gladfelter


Occultations of bright planets and stars (magnitude 3.3 or brighter) for April, 2019 through 2020

All dates and times are MST

Only events visible from western South Dakota are listed.

Times listed below are valid for observers at the Journey Museum in Rapid City.


Occultation of 123 zeta Tau 2.97 by moon 31% illuminated, phase= 293 degrees

8/25/2019 start 4:17:03.8, ends 4:40:58.9


Occultation of 13 mu Gem 2.87 by moon 98% illuminated, phase= 194 degrees

12/13/2019 start 02:25:22.7, end 03:19:52.7


Occultation of 13 mu Gem 2.87 by moon 88% illuminated at phase= 139 degrees

02/05/2020 start 22:00:45.3, end 22:23:05.5


Occultation of Mars 1.2 by moon 24% illuminated at phase= 302 degrees:

02/18/2020 04:45:24.6 Start Partial

02/18/2020 04:45:37.4 Start Total

02/18/2020 06:05:51.1 End Total

02/18/2020 06:06:05.4 End Partial


Occultation of Acrab 2.56 by moon 28% illuminated at phase= 64 degrees

09/21/2020 18:26:19.7 Start Total, 19:22:55.6 End Total


Occultation of Venus -3.9 by moon 5% illuminated at phase= 335 degrees

This event occurs during daylight hours and may be visible using a telescope IF EXTREME CAUTION IS EXERCISED!

12/12/2020 14:24:27.3 Start Partial

12/12/2020 14:24:56.8 Start Total

12/12/2020 15:18:18.2 End Total

12/12/2020 15:18:45.3 End Partial


Notes about occultations:  The timing is very specific to your exact location.  Few clocks can be relied on to be accurate at the sub-second level, including the inexpensive radio-controlled clocks which are typically corrected once per day around midnight, also note that the clock display on a computer or phone is typically corrected infrequently.  The accuracy of a clock can be verified by time signals broadcast on shortwave frequencies, or by using a GPS receiver, or by accessing a network time server on the Internet if you have software specifically designed for this purpose. However, it is very difficult to visually determine the exact time when a star appears or disappears at the illuminated limb of the moon.  Photography, therefore, is very helpful.


If you need data for your particular location, please send me an email with the latitude, longitude, and preferably also your altitude above mean sea level in meters or feet, for your observing location.  Please specify the units you use, such as degrees and meters and specify North or South, East or West for your coordinates.




High Precision Daily Polynomial Coefficients for Lunar Coordinates



The Astronomical Almanac lists the apparent right ascension, apparent declination, and true distance (light time not factored in) of the moon at zero hours Terrestrial Time for each day of the year.  The online web site at http://asa.usno.navy.mil/SecD/LunarPoly.html gives daily polynomials for apparent right ascension, apparent declination, and horizontal parallax for any desired time during the day listed.  However, there are a few points to consider: (1) the polynomials for 2019 are not yet posted as of April 11.  (2) The coefficients for horizontal parallax have not had the required number of significant figures to match the distance listed in the Astronomical Almanac.  (3) Their daily polynomials have never been listed for years beyond the current year.


Posted here is a text file for 2019-2020 giving the daily coefficients for apparent Right Ascension, apparent Declination, True Distance, and Horizontal Parallax,   The distance is the true distance in kilometers (light time not factored in).  The others are in degrees.  Each quantity is to be computed as:

                quantity = A0 + A1f + A2f2 + ... + A5f5

                where f = h/24, with h = time (TT) in hours

                so that  0.0  <=   f   <  1.0


The results for the angular coordinates should agree very closely with the apparent coordinates as listed in the Astronomical Almanac, section D, and the distance should agree within a few meters. In late March, the coefficients of the polynomials were recomputed so as to minimize any discontinuity in the calculation of any quantity at the boundary between one day and the next.


If you have any questions, comments, or needs concerning these polynomials, please send an email to:   g e o r g e 0 7 @ r a p . m i d c o . n e t  (omit imbedded spaces).