scem.1 (4629B)
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If not, see <http://www.gnu.org/licenses/>. 15 .Dd October 17, 2025 16 .\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""" 17 .Dt SCEM 1 18 .Os 19 .\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""" 20 .Sh NAME 21 .Nm scem 22 .Nd compute the position of the sun 23 .\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""" 24 .Sh SYNOPSIS 25 .Nm 26 .Op Fl DhVvr 27 .Op Fl a Ar algo 28 .Op Fl d Ar utc_date 29 .Ar latitude 30 .Ar longitude 31 .\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""" 32 .Sh DESCRIPTION 33 .Nm 34 computes the position of the sun relative to a given point on the Earth's 35 surface, on a given date. 36 .Pp 37 The latitude must be in [-90, 90] degrees relative to the equator. 38 It is positive towards the north. 39 The longitude must be in [-180, 180] degrees relative to Greenwich. 40 The angle is positive towards the east. 41 .Pp 42 The output depends on two options, 43 .Fl D 44 and 45 .Fl V . 46 If 47 .Fl D 48 is not provided, 49 .No 50 outputs the position of the sun in elevation and azimuth to the standard 51 output with the following format: 52 .Bd -literal -offset Ds 53 "%f %f\\n", elevation, azimuth 54 .Ed 55 .Pp 56 The elevation angle is in [-90, 90] degrees. 57 It defines the elevation of the sun relative to the horizon. 58 The azimuth angle is in [0, 360] degrees, with 0° indicating north, 59 90° east, 60 180° south, 61 and 270° west. 62 .Pp 63 If 64 .Fl V 65 is provided, 66 .Nm 67 outputs the direction from the sun as a 3D vector to the standard output 68 with the following format: 69 .Bd -literal -offset Ds 70 "%f %f %f\\n", vec[0], vec[1], vec[2] 71 .Ed 72 .Pp 73 The options are as follows: 74 .Bl -tag -width Ds 75 .\"""""""""""""""""""""""""""""""""""""" 76 .It Fl a Ar algo 77 Defines the algorithm to be used to calculate the position of the sun. 78 By default, use the 79 .Cm meeus 80 algorithm. 81 .Pp 82 The solar position algorithms are as follows: 83 .Bl -tag -width Ds 84 .It Cm meeus 85 The algorithm described in Jean Meeus' book, 86 .Dq Astronomical Algorithms . 87 .It Cm psa 88 The algorithm developed by the 89 .Dq Plataforma Solar de Almería . 90 .El 91 .\"""""""""""""""""""""""""""""""""""""" 92 .It Fl D 93 Suppress the sun direction from the output. 94 .It Fl d Ar utc_date 95 Date on which the position of the sun is calculated at the specified 96 location. 97 Must be defined in Coordinated Universal Time 98 .Pq UTC+00:00 . 99 By default, use the local date. 100 .Pp 101 The date must be in the format 102 .Dq YYYY-MM-DDThh:mm:ss , 103 i.e., as printed for the current date by the following date command: 104 .Bd -literal -offset Ds 105 date -u +"%Y-%m-%dT%H:%M:%S" 106 .Ed 107 .\"""""""""""""""""""""""""""""""""""""" 108 .It Fl h 109 Output short help and exit. 110 .\"""""""""""""""""""""""""""""""""""""" 111 .It Fl V 112 Add the 3D vector from the sun to the observer to the output with the first, 113 second and third components pointing east, north and up, respectively. 114 .It Fl v 115 Make 116 .Nm 117 verbose. 118 .\"""""""""""""""""""""""""""""""""""""" 119 .It Fl r 120 Output the solar direction in radians rather than degrees. 121 Meaningless if 122 .Fl D 123 is defined. 124 .El 125 .\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""" 126 .Sh EXIT STATUS 127 .Ex -std 128 .\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""" 129 .Sh EXAMPLES 130 Compute the current position of the sun for a latitude of 43.559962° north and a 131 longitude of 1.468150° east. 132 Output both the direction in radians and the corresponding 3D vector: 133 .Bd -literal -offset Ds 134 scem -V -r 43.559962 1.468150 135 .Ed 136 .Pp 137 Same location as above, setting the observation date to October 21, 2015, at 138 11:28:00 AM UTC+2. 139 Output the 3D vector only: 140 .Bd -literal -offset Ds 141 scem -D -V -d 2015-10-21T09:28:00 43.559962 1.468150 142 .Ed 143 .\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""" 144 .Sh SEE ALSO 145 .Rs 146 .%A Jean Meeus 147 .%B Astronomical Algorithms 148 .%D 1991 149 .Re 150 .Rs 151 .%A Manuel Blanco 152 .%A Kypros Milidonis 153 .%A Aristides Bonanos 154 .%T PSA+ updated PSA sun position algorithm 155 .%U https://github.com/CST-Modelling-Tools/Updated-PSA-sun-position-algorithm 156 .%D 2025 157 .Re