Phases by Fanel Donea
Click here to download Phases.
[a PC MSDOS program in a self-extracting archive]
This text first appeared in 'International Amateur-Professional Photoelectric
Photometry (IAPPP) Communications' No.57 , p40-42 , Autumn 1994
Thanks are due to Dr.Terry Oswalt , editor of IAPPP Comm. , for
the permission to reproduce it.
PHASES - a program helping the eclipsing binary observer
============================================================
Fanel Donea , Astronomical Institute , Bucharest , Romania
fdonea@mpifr-bonn.mpg.de,
fdonea@roimar.imar.ro
The program computes heliocentrical phases , hour angles and horizon system
positions of known eclipsing binaries for a given period of time with a given
time step and , in addition , some data concerning the Moon's phase ( fraction
illuminated , from 0.0 to 1.0) and its position in the sky. It also computes
the angle to the Moon's direction for each star. The stars' names and
coordinates are read from an input file.
An observer (especially an amateur,using a small telescope) might find this
simple utility program useful for several reasons.
First of all , the pre-computed hour angle may help finding the star
( sidereal clocks can go wrong or , in the case of amateurs , may even
be absent ).
Knowing beforehand the altitude and azimuth angle of the star is also
useful. Observations made under a certain altitude are bad , or simply
impossible because the star is set or because of hindering terrestrial objects.
The azimuth angle is measured , like hour angles , from the South , westerly
(S=0 degrees , W=90 ,N=180..).
There may sometimes be mistakes when summer time is used ( deciding quickly
about adding or subtracting one hour may result into errors ). The program
avoids this by indicating civil time ( the time read on watches,either in the
summer or winter time ). It automatically detects whether a summer schedule is
in use or not. It's based on the assumption that , for a certain year , clocks
are put forward by one hour at 00:00 hours , the last Sunday in March ( 00:00
becomes 01:00 ) and back again by one hour at 00:00 hours , the last Sunday
in September (when 01:00 becomes 00:00).
The position of the Moon on the night sky is ,of course ,of great importance
to the observer.Full moon close to the observed region is evidently something
to be avoided .That added to the table Moon's phase , Moon's coordinates and
the 'angle to the Moon'='atm' column for each star. There is some redundancy
but that's always better than having to compute by hand.
Finally , there may be a need to observe specifically a given phase interval
( intervals missing from the light curve or interesting minima ).
The program makes all its calculations starting approximately at dusk and
ending at dawn ,thus covering only the interval when observations are possible
(if there is one). Civil twilight is used here (altitude of the Sun = -6 deg);
though not all stars are visible until the end of astronomical twilight
(altitude of the Sun = -18 degrees), some bright stars may be visible already,
before it gets completely dark.
The program can also be used to monitor approximately positions of objects
other than eclipsing binaries , provided they have relatively constant
equatorial coordinates. Non zero dummy minimum and period should then be
entered in the input file , and the 'PHASE' column in the output should be
ignored.
The input file could look like this :
------------------------------------------------------------------------------
GO_Cyg 2446351.3280 0.7177632 20 36 54 35 24 0
BV_Dra 2445739.1145 0.3500710 15 11 42 61 53 0
------------------------------------------------------------------------------
| | | | |
| | | | |
(6 char name) (HJD of minimum) (period,d) RA(h,min,sec),DEC(deg,min,sec)
Negative declinations should be entered with degrees,minutes and seconds all
negative. For instance , -20.25 degrees should be entered as -20 -15 0.
All numerical formats are accepted as long as numbers are separated by blank
characters. The name of the star should be 6 characters long with no blank.
The number of stars is guessed by the program , and , even with 4 or 5 stars,
printing the output file will still be possible on most printers.
A sample output is , for instance (for GO Cyg and BV Dra , 2 nights starting
on 1-JAN-1994 , time step=60 min ) :
------------------------------------------------------------------------------
***********************************
* *
* Phases of GO_Cyg and BV_Dra *
* *
***********************************
Computed for 2 consecutive nights starting 1-JAN-1994
LONGITUDE = -26.096312 degrees
LATITUDE = 44.413889 degrees
LOCAL TIME - U.T. = 2.00 hours
GO_Cyg :
========
Min = 2446351.328000 d T= 0.717763 d
R.A.= 20.615000 h Decl.= 35.400000 deg
BV_Dra :
========
Min = 2445739.114500 d T= 0.350071 d
R.A.= 15.195000 h Decl.= 61.883333 deg
Civil time is supposed to be one hour ahead of local time from the last
Sunday in March until the last Sunday in September.
( 'atm' = angle to the Moon , 'Lmst'=local mean sidereal time )
Night 1 of 2
*********** Saturday , 1-JAN-1994 / Sunday , 2-JAN-1994 *****************
TIME GO_Cyg BV_Dra Moon
Civil Lmst phas h.ang alt azm atm phas h.ang alt azm atm phs alt azm
17:00 23:28 0.54 02:51 56 90 134 0.51 08:16 25 154 79 0.8 -33 210
18:00 00:28 0.60 03:51 46 99 134 0.63 09:16 21 161 79 0.8 -27 225
19:00 01:28 0.66 04:51 35 108 134 0.75 10:17 18 168 79 0.8 -19 238
20:00 02:29 0.72 05:52 25 116 134 0.87 11:17 17 175 79 0.8 -10 249
21:00 03:29 0.78 06:52 16 124 134 0.98 12:17 16 182 78 0.8 -0 260
22:00 04:29 0.84 07:52 8 134 134 0.10 13:17 17 189 78 0.8 10 270
23:00 05:29 0.89 08:52 0 144 134 0.22 14:17 20 196 78 0.8 20 281
00:00 06:29 0.95 09:52 -5 154 133 0.34 15:17 23 203 78 0.8 30 293
01:00 07:29 0.01 10:52 -9 166 133 0.46 16:18 28 209 78 0.8 39 306
02:00 08:29 0.07 11:53 -10 179 133 0.58 17:18 34 214 78 0.8 46 323
03:00 09:30 0.13 12:53 -9 191 133 0.70 18:18 40 218 78 0.8 50 344
04:00 10:30 0.18 13:53 -6 203 133 0.82 19:18 47 221 78 0.8 51 7
05:00 11:30 0.24 14:53 -1 214 133 0.94 20:18 54 221 78 0.8 48 28
06:00 12:30 0.30 15:53 6 224 133 0.06 21:18 61 219 78 0.8 41 46
07:00 13:30 0.36 16:53 14 234 133 0.17 22:19 67 211 78 0.8 33 61
Night 2 of 2
*********** Sunday , 2-JAN-1994 / Monday , 3-JAN-1994 *****************
TIME GO_Cyg BV_Dra Moon
Civil Lmst phas h.ang alt azm atm phas h.ang alt azm atm phs alt azm
17:00 23:32 0.94 02:55 56 90 132 0.36 08:20 25 155 77 0.8 -42 197
18:00 00:32 0.00 03:55 45 100 132 0.48 09:20 21 161 77 0.8 -37 215
19:00 01:32 0.05 04:55 34 108 132 0.60 10:21 18 168 77 0.7 -30 230
20:00 02:32 0.11 05:56 25 116 132 0.72 11:21 17 175 77 0.7 -22 243
21:00 03:33 0.17 06:56 15 125 131 0.84 12:21 16 183 77 0.7 -12 255
22:00 04:33 0.23 07:56 7 134 131 0.96 13:21 18 190 77 0.7 -2 265
23:00 05:33 0.29 08:56 0 144 131 0.08 14:21 20 197 77 0.7 8 276
00:00 06:33 0.34 09:56 -5 155 131 0.20 15:21 24 203 77 0.7 18 287
01:00 07:33 0.40 10:56 -9 167 131 0.32 16:22 29 209 77 0.7 27 298
02:00 08:33 0.46 11:57 -10 179 131 0.44 17:22 34 214 77 0.7 36 312
03:00 09:34 0.52 12:57 -9 192 130 0.55 18:22 41 218 77 0.7 42 329
04:00 10:34 0.58 13:57 -6 204 130 0.67 19:22 47 221 77 0.7 45 349
05:00 11:34 0.63 14:57 -1 215 130 0.79 20:22 54 221 77 0.7 45 9
06:00 12:34 0.69 15:57 6 225 130 0.91 21:22 61 219 77 0.7 42 29
07:00 13:34 0.75 16:57 14 234 130 0.03 22:23 68 210 77 0.7 35 46
The program is written in standard C language and is freely available
in IBM PC format from the author. Some parts of the source code could
also be available.