A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
USNO MICA almanac program user report
From: Paul Hirose
Date: 2003 Jun 7, 13:02 -0700
From: Paul Hirose
Date: 2003 Jun 7, 13:02 -0700
I recently purchased the U.S. Naval Observatory's MICA software, version 1.52. MICA runs on both DOS and Macintosh machines, and can generate most of the data tabulated in the Astronomical Almanac. http://aa.usno.navy.mil/software/mica/micainfo.html MICA's not a complete AA implementation. It doesn't do planetary satellites (except Earth's) and minor planets (asteroids). Nor will it compute eclipse data. So what does MICA do? It's got the sun, moon, planets, and many stars. It can produce a table of positions, with Astronomical Almanac accuracy, for any one of these bodies at a user-specified time interval. The time step may be specified in days, hours, minutes, or seconds. The smallest time step is .1 second. There are many choices for the place, origin, and frame of the output coordinates. "Place" may be geometric, astrometric, or apparent. "Origin" may be topocentric, geocentric, heliocentric, or barycentric. "Frame" may be equator of date, ecliptic of date, equator of 2000.0, ecliptic of 2000.0, or the local horizon. Not all possible combinations of those parameters are available, since some don't make sense or aren't used. Regrettably, only two time scales are available: UT1 and TDT. There's no user access to the TDT vs. UT1 correction factor. MICA obtains this from a table which apparently is hardwired into the program. An appendix in the manual shows the table, and the extrapolated portion is out of date. For example, for mid 2003 the table shows TDT 69 seconds ahead of UT1. The true value is around 64.2. So if you request a body's UT1 coordinates, they're being computed for a time about five seconds ahead of what you asked for. It's enough to shift the Moon's position 2.5 seconds of arc. Using TDT is not a complete cure. Topocentric coordinates will be incorrect since they depend of the rotational position of Earth and thus the TDT-UT1 table rears its head again. To get around this you must get the offset from the Web, examine the table in the manual to determine what MICA thinks the offset is, then fudge the observer's longitude to compensate for the discrepancy. And remember, on top of this you're using a time scale more than a minute ahead of UTC and UT1. It's a shame MICA has no means to update the TDT - UT1 table, or at least a way to enter the offset manually. Offering the UTC time scale would be an improvement too. Of course that would require a manual input for DUT1. MICA calculates local times of rise, set, and twilight, but that's all it does in local time. I think all positional calculations should be possible in local time. Particularly so since the stated audience for the program includes lawyers and accident investigators. These folks, and navigators, will be annoyed that MICA outputs horizontal coordinates with zenith distance, not altitude. If you're willing to tolerate that, it's possible to do celestial nav sight reduction with MICA. In fact, there's a chapter on that in the book. MICA's horizontal coordinates don't take refraction into account, so you still have to make that correction to your sextant reading. I mentioned "many stars". MICA has several catalogs of star or star-like objects. 1. The 57 navigational stars. 2. A 1535-star subset of the FK5 catalog. 3. A set of 233 extragalactic radio sources. 4. The Messier catalog. 5. A set of 1482 bright stars. Each catalog is indexed three different ways for convenience. For example, if the navigational star catalog is the active one, Rigel may be loaded by typing in that name, or BET ORI (beta Orionis), or 11 (its navigational star number). The catalogs are ASCII files and the manual describes the format so you can build your own catalog files. The format includes fields for proper motion and parallax, to enable positions to be calculated with high accuracy. Speaking of the manual, it's a well-written 6" x 9" 140-page hardbound book - quite refreshing in this age of "here's the PDF, print it yourself". Windows users will have a bit of a shock, though. MICA runs in a DOS window and is controlled entirely through the keyboard. You'll have to fight the urge to reach for your mouse. For all that, I'm fairly satisfied with the interface. After installing the software, you can set the book aside and start running MICA. Just about everything is obvious, though some settings are a bit clumsy to adjust. The output goes to the screen by default but may be directed to a file. A table up to 1000 lines can be produced at one go, but there's a command to continue the table seamlessly (no header inserted again) from where it left off. To allow its use as an astrometric engine, the DOS version of MICA may be run from a batch file. The MICA control files are ASCII files, but their names (one file for setup, one for execution) are fixed. Therefore, multiple invocations of MICA from a DOS batch file will require file renaming to change MICA's parameters. Though it's got flaws, I recommend MICA for celestial buffs, especially those needing authoritative "ground truth" data to validate their own software. The price is right, just $25 from Willmann-Bell. http://www.willbell.com/almanacs/almanac_mica.htm I've read MICA 2.0 will span the years 1850 - 2050, vs. 1990 - 2005 at present. If they can do that and fix the problems I pointed out, it should be a marvelous program.