The first line is an "echo" of some of the input values from the control file, for example:
30.334 97.760 520. Austin, Texas 2000 3.5 15 F F T T T
The latitude, longitude, height, and site name are listed. The epoch of RA and Dec is given. The magnitude cut-off and altitude cut-off are given. The five true/false flags are given.
The next line gives the date and time zone, for example:
*** 1996 June 2 Sun evening *** Times are PM CDT *** 2116 558
For the prediction date of July 26, the evening predictions are for Thursday. The predictions times are PM for the time zone CDT (Central Daylight Time). Note, CST stands for Central Standard Time. The value 2116 is the local time of twilight when the sun is 10 degrees below the horizon. The value 558 is the local time of morning twilight when the sun is 10 degrees below the horizon. These two times are given using a 24-hour clock, so on the prediction date, evening twilight ends at 9:16 PM CDT, and morning twilight starts at 5:58 AM CDT the following morning.
The next line gives the titles for each data line:
H M S Tim Al Azi C Dir Mag Dys F Hgt Shd Rng EW Phs R A Dec
Each of these fields is discussed below.
A header line containing information about an object is output above the predictions for that object, for example:
20625 Cosmos 2082 Rk 90 46B 10.4 3.9 23 2.5 p 2.0 var 2.5
The object's NORAD catalog number is given. The object's name is given. The object's International Designation (ID) is given. The three size values, the RCS value, and the computed intrinsic magnitude at full phase and 1000 Km (derived from the sizes) are given if they are available. The class value is given. The observed intrinsic magnitude is given (if available). Finally, the comments field from the intrinsic magnitudes file is given.
Each set of predictions has the following form:
H M S Tim Al Azi C Dir Mag Dys F Hgt Shd Rng EW Phs R A Dec 9 41 54 18 36 261 67 4.0 31 4 536 493 829 .9 115 1251 10.7 9 43 22 18 41 297 C 92 3.9 31 4 536 499 759 1.0 123 1234 38.7 9 44 49 18 34 331 117 4.3 31 4 537 505 855 1.0 124 1140 64.9
H, M, and S are the hour, minute, and second, respectively of the prediction point.
The Tim value is the estimated uncertainty in the time of prediction. So 18 indicates 18 seconds "likely" error in the prediction. (In this case the orbital elements are 31 days old. This is unusual.) If the extimated uncertainty is less than or equal to 4 seconds, the field is left blank.
The Al value is the altitudinal angle (elevation angle) in degrees of the prediction point. The Azi value is the azimuthal angle (bearing angle) in degrees of the prediction point.
A letter C after the azimuth indicates that this is the point of culmination. The absence of the C would indicate that this is not a culmination prediction point.
The Dir value is the direction that the satellite is traveling. A value of 0 means traveling "up". A value of 90 means "right". A value of 180 means "down". A value of 270 means "left". In the given example, the satellite travels right and a little up from the southwest until the culmination point is reached. Then it travels right and a little down as it moves into the northwest.
The Mag value is the predicted maximum magnitude if an observed intrinsic magnitude was available. This does not mean that the satellite cannot be brighter or fainter than this magnitude. The satellite can be brighter if it reflects the sun better than expected at this phase angle. It can be fainter than expected if it reflects the sun worse than expected at this phase angle or if it is a non-spherical object and its particular orientation is unfavorable on this pass. Since the comment "var 2.5" appears, then it is likely that the object can change in brightness from this "maximum predicted magnitude" to a brightness that is 2.5 magnitudes fainter. Often such a variation will take place in less than 2 minutes. If "var att" appears, then the object varies very slowly and is usually constant at some brightness equal to or less than the prediction. However, the comment "var att" applies to a large percent of all objects, so it is not normally explicitly included as a comment.
If an observed intrinsic magnitude is not available, then the special value "20" is used for the intrinsic magnitude. This will normally produce a predicted magnitude between 18 and 24. If the observer has an expectation of the intrinsic brightness because of a knowledge of the expected size, then this "20" magnitude can be transformed as follows: 20 is subtracted and the expected intrinsic magnitude is added. For example, if 20.4 appears, but the observer expects an intrinsic magnitude of 3.5, then 20.4 - 20 + 3.5 = 3.9 and the expected magnitude is 3.9. If the object is observed to be about 4.4, then an intrinsic magnitude of 4.0 would be appropriate.
H M S Tim Al Azi C Dir Mag Dys F Hgt Shd Rng EW Phs R A Dec 9 41 54 18 36 261 67 4.0 31 4 536 493 829 .9 115 1251 10.7 9 43 22 18 41 297 C 92 3.9 31 4 536 499 759 1.0 123 1234 38.7 9 44 49 18 34 331 117 4.3 31 4 537 505 855 1.0 124 1140 64.9
The Dys value is the number of days from the epoch of the elements to the prediction date.
The F value is the fraction of a revolution (in tenths) that the object has made since its last perigee. A fractional value of 9, 0, or 1 indicates that the object is near perigee. A fractional value of 4, 5, or 6 indicates that the object is near apogee. A value of 2 indicates the object is rising from perigee to apogee.
The Hgt value is the height of the object in miles.
The Shd value is the height of the object above the Earth's shadow in miles.
The Rng value is the range of the object in miles.
The EW value is the distance east/west that the orbital plane moves in one minute. If this satellite is one minute early, it will be 1.0 degrees to the east of the predicted position. If it is one minute late, it will be 1.0 degrees west of the predicted position.
The Phs value is the sun-object-observer angle. A value of 0 indicates full phase, a value of 180 indicates new phase.
The R A value is the right ascension of the prediction.
The Dec value is the Declination of the prediction.