marstimeglobal
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Contents: Description, Arguments, Usage, Examples, Sub-Functions, Related Functions, Source Supported Under Version: > 1.13
Description Returns information on Mars global time parameters, including solar longitude
Arguments and Return Values
Usage Syntax: marstimeglobal(Dt) For input, this function takes the J2000 TT offset - the number of days since noon Terrestrial Time (TT) on January 1, 2000. To get the current offset (assuming your computer's clock is accurate), use MJD2Dt(MJD(clock(1))). The accuracy of the outputs depends on the accuracy of the input time. If you are using the current system time, that means the outputs are only as accurate as your system clock. Most of the equations used in these Mars time calculations are adapted from NASA GISS Mars24 (available at http://www.giss.nasa.gov/tools/mars24/) and Allison, M., and M. McEwen (2000), A post-Pathfinder evaluation of aerocentric solar coordinates with improved timing recipes for Mars seasonal/diurnal climate studies, Planet. Space Sci., 48, 215-235, doi:10.1016/S0032-0633(99)00092-6 (available at http://pubs.giss.nasa.gov/cgi-bin/abstract.cgi?id=al05000n). The Mars24 pages have good explanations of the physical meaning of the various martian time quantities, as well as an overview of martian timekeeping. The function will return a structure with the global Mars time parameters for the input time. They are: Dt: J2000 TT offset, in days (this is just the input) M: Mean anomaly of Mars, in degrees; accurate within 0.001 degrees aFMS: Angle of Fiction Mean Sun, in degrees; accurate within 0.001 degrees PBS: Longitudinal perturbation, in degrees; accurate within ~0.007 degrees EoC: Equation of center (true anomaly minus mean anomaly), in degrees; accurate within ~0.007 degrees nu: True anomaly of Mars, in degrees; accurate within ~0.008 degrees R: Distance from the Sun to Mars, in AU; accurate within ~0.0001 AU hlon: Heliocentric longitude of Mars, in degrees; accurate within ~0.01 degrees hlat: Heliocentric latitude of Mars, in degrees; accurate within ~0.0003 degrees LS: Areocentric solar longitude, in degrees; accurate within 0.008 degrees NOTE that for the following three time quantities, due to 0.004 degrees of uncertainty (1 part in 90,000) in the inertial location of the martian prime meridian, there is an uncertainty of 1 second (2.7e-4 hr, or 1.1e-5 sol) in all of these quantities, in addition to the theoretical limits given below. EoT: Equation of Time, in (martian) hours; accurate within 3 s (0.000833 hr) MSD: Mars Sol Date, in sols; accurate within 0.1 s (1.2e-6 sol) MTC: Coordinated Mars Time, in (martian) hours; accurate to 0.1 s (0.000028 hr) ssplon: Planetocentric longitude of subsolar point, in degrees; accurate within ~0.013 degrees decl: Declination (planetocentric latitude of subsolar point), in degrees; accurate within ~0.0035 degrees The stated accuracy ranges are only applicable between 1900 and 2100. Outside that range, the returned values should be considered to be questionable. Most values in the returned structure are single precision (float format), since the values cannot be determined to enough significant figures to warrant double precision. When marstimeglobal() is entered without any arguments, it prints its description, as shown below.
Examples dv> marstimeglobal() Calculates global Mars time data, given J2000 TT offset (in days) marstimeglobal(Dt), where Dt is the number of days since J2000 TT Fields in returned structure (all angles in degrees): Dt: J2000 TT offset, in days (the input); as accurate as the input M: Mean anomaly; accurate within 0.001 degrees aFMS: Angle of Fiction Mean Sun; accurate within 0.001 degrees PBS: Longitude perturbation angle; accurate within ~0.007 degrees EoC: Equation of center (true anomaly minus mean anomaly); accurate within ~0.007 degrees nu: True anomaly; accurate within ~0.008 degrees R: Distance from the Sun to Mars, in AU; accurate within ~0.0001 AU hlon: Heliocentric longitude of Mars; accurate within ~0.01 degrees hlat: Heliocentric latitude of Mars; accurate within ~0.0003 degrees LS: Areocentric solar longitude; accurate within 0.008 degrees EoT: Equation of Time, in hours; accurate within 3 s (0.000833 hr) MSD: Mars Sol Date, in sols; accurate within 0.1 s (1.2e-6 sol) MTC: Coordinated Mars Time, in hours; accurate to 0.1 s (0.000028 hr) ssplon: Planetocentric longitude of subsolar point; accurate within ~0.013 degrees decl: Declination (planetocentric latitude of subsolar point); accurate within ~0.0035 degrees All stated accuracies are for dates between 1900 and 2100, provided the input time is exact. Outside that range, questionable accuracy. See http://www.giss.nasa.gov/tools/mars24/help/algorithm.html and http://pubs.giss.nasa.gov/cgi-bin/abstract.cgi?doi=10.1016/ S0032-0633(99)00092-6 S. Marshall 11-10-2009 0 dv> MJD2Dt(MJD(clock(1))) 3616.56492959585 dv> marstimeglobal(MJD2Dt(MJD(clock(1)))) struct, 15 elements Dt: 3616.56493641395 M: 114.542068481445 aFMS: 5.60520267486572 PBS: -0.00852344185113907 EoC: 9.23740196228027 nu: 123.779472351074 R: 1.59311711788177 hlon: 99.8689727783203 hlat: 1.36212980747223 LS: 14.8426046371460 EoT: -0.525308668613434 MSD: 48311.4206354473 MTC: 10.0952510833740 ssplon: 36.4508705139160 decl: 6.26008605957031 |
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Recent Library Changes Created On: 11-18-2009 |
