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Forum Index : Microcontroller and PC projects : MMX - lunar occultation of a star
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| cdeagle Senior Member  Joined: 22/06/2014 Location: United StatesPosts: 261 |
This post describes a MMBASIC program for the MicroMite MMX, Raspberry Pi and DOS platforms which can be used to predict occultations of a star by the Moon. A lunar occultation occurs whenever the Moon moves across the location of another celestial object. Here is a typical user interaction with the program, star_occult.bas, and the results provided. lunar occultation of a star =========================== Spica please input the calendar date (month [1 - 12], day [1 - 31], year [yyyy]) < for example, october 21, 1986 is input as 10,21,1986 > < b.c. dates are negative, a.d. dates are positive > < the day of the month may also include a decimal part > ? 2,1,1987 please input the geographic latitude of the observer (degrees [-90 to +90], minutes [0 - 60], seconds [0 - 60]) (north latitudes are positive, south latitudes are negative) ? 40,0,0 please input the geographic longitude of the observer (degrees [0 - 360], minutes [0 - 60], seconds [0 - 60]) (east longitude is positive, west longitude is negative) ? -105,0,0 please input the altitude of the observer (meters) (positive above sea level, negative below sea level) ? 0 please input the number of days to simulate ? 30 searching for occultation conditions ... begin occultation conditions ---------------------------- calendar date February 18 1987 utc time 12 hours 26 minutes 13.32 seconds utc julian day 2446845.01820969 topocentric coordinates lunar azimuth angle 213 deg 43 min 59.35 sec lunar elevation angle 32 deg 45 min 24.36 sec lunar phase 79.27 end occultation conditions -------------------------- calendar date February 18 1987 utc time 13 hours 15 minutes 56.89 seconds utc julian day 2446845.05274173 topocentric coordinates lunar azimuth angle 225 deg 34 min 30.72 sec lunar elevation angle 26 deg 37 min 43.62 sec lunar phase 78.97 event duration 0 hours 49 minutes 43.57 seconds The celestial coordinates of the star of interest are defined by the user in a subroutine called star_data. The following illustrates the coordinates for the star Spica. Note that the value for the star's declination in degrees is input as a string. This allows the software to compute the correct "sign" for declination. sub star_data ' star coordinates subroutine ''''''''''''''''''''''''''''' local rasc_hr, rasc_min, rasc_sec local decl_deg$ as string, decl_min, decl_sec local decl.deg ' star name star_name$ = "Spica" ' j2000 right ascension (hours, minutes, seconds) rasc_hr = 13.0 rasc_min = 25.0 rasc_sec = 11.587.0 ' j2000 right ascension (radians) rasc_star = (15.0 * dtr) * (rasc_hr + rasc_min / 60.0 + rasc_sec / 3600.0) ' j2000 declination (degrees, minutes, seconds) ' (note: input declination in degrees as a string) decl_deg$ = "-11.0" decl_min = 9.0 decl_sec = 40.71 decl.deg = val(decl_deg$) ' j2000 declination (radians) if (left$(decl_deg$, 1) = "-" and decl.deg = 0.0) then decl_star = -dtr * (decl_min / 60.0 + decl_sec / 3600.0) elseif (decl.deg = 0.0) then decl_star = dtr * (decl_min / 60.0 + decl_sec / 3600.0) else decl_star = dtr * sgn(decl.deg) * (abs(decl.deg) + decl_min / 60.0 + decl_sec / 3600.0) end if end sub Here is a zip archive of the MMBASIC source code, the PDF document for the MATLAB version and several data files for other stars. 2017-07-24_120438_star_occult.zip |
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