JEphem           Presentation    Ephemeris    SkyMap    Curve    Date search    Informatic    Library    Download    Glossary    About
	JEphem Ephemeris trail

	Ephemeris trail
	Here, the purpose is to present the astronomical notions used by JEphem, and how they were included in the program. The building process of the program is described.

Contents

• Introduction : desired features, future developments, main information sources.



• Generalities about ephemeris calculation : how is performed ephemeris calculation today ? who is doing it ? What to use for JEphem ?



• Theories used in JEphem :


• VSOP87 : this theory from the BDL has been used to compute planetary positions, from Mercury to Neptune.
• Building VSOP87 : a class, BuildVSOP87, has been written to build data classes and files from BDL original files.
• Truncating VSOP87 : if we sum all the terms provided in the BDL original files, we have a precision of 0.003 arcsecond (compared with DE405). This precision is not always necessary and the computation is slow. So we need a way to select terms.
• Testing VSOP87 : what is JEphem worth? classes have been written to compare JEphem's results with reference computations.


• Pluto 99 : one of the BDL's theory, used to compute Pluto coordinates.



• ELP 2000-82B : an other theory from the BDL, used to compute Moon coordinates.



• Class organization : a first view of JEphem classes, handling these notions.



• Frames :


• Reference frames



• Coordinate transformations



• Handling frames : how frames were included in JEphem.



• Handling precision



• Units : to display coordinates we need to handle different units.



• Handling time : julian days, legal time, UTC, TAI, TDB... The different times used to develop JEphem are presented here.



• Putting all together : an overwiew of JEphem astronomical classes.



• Swiss Ephemeris : an other astronomy software that I included in JEphem for test purposes.