Understanding VSOP87 Column Names: BDL File Structure & Explanation

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In summary, the VSOP87 files in the BDL server contain one file per planet and version, with a variable number of terms for each planet. These terms correspond to the heliocentric coordinates and velocities for each planet at a given time (T). The columns in the file represent the X, Y, Z, U, V, and W components of the heliocentric coordinates and velocities. The formula provided can be used to calculate the velocities from the terms in the BDL file.
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Philosophaie
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VSOP87 files
In BDL server, we find one file per planet. Here is an extract of VSOP87 file (for Neptune, version A) :

VSOP87 VERSION A1 NEPTUNE VARIABLE 1 (XYZ) *T**0 772 TERMS HELIOCENTRIC DYNAMICAL ECLIPTIC AND EQUINOX J2000
1810 1 0 0 0 0 0 0 0 1 0 0 0 0 -0.00682678287 30.05889926953 30.05890004476 5.31211340029 38.13303563780
1810 2 0 0 0 0 0 0 0 0 0 0 0 0 0.00000000000 -0.27080164222 0.27080164222 3.14159265359 0.00000000000
etc...
1810 771 0 0 0 0 6-16 0 2 0 0 0 0 0.00000001037 -0.00000001976 0.00000002232 2.42169508541 158.37366516480
1810 772 0 0 0 0 0 0 19-20 0 0 0 0 0.00000000619 0.00000002392 0.00000002471 3.93681150847 658.18966002270

VSOP87 VERSION A1 NEPTUNE VARIABLE 1 (XYZ) *T**2 102 TERMS HELIOCENTRIC DYNAMICAL ECLIPTIC AND EQUINOX J2000
1812 1 0 0 0 0 0 0 0 0 0 0 0 0 0.00000000000 0.00005371138 0.00005371138 0.00000000000 0.00000000000
1812 2 0 0 0 0 0 0 1 -1 0 0 0 0 0.00004488541 0.00000656405 0.00004536283 5.02700751836 36.64856292950
etc...
1812 101 0 0 0 0 1 0 0 -1 0 0 0 0 0.00000001759 -0.00000001439 0.00000002273 5.59760233612 491.55792945680
1812 102 0 0 0 0 0 3 0 -4 0 0 0 0 -0.00000002773 -0.00000000305 0.00000002790 1.90430778774 487.36514376280
etc..

The second row is n.
Rows 3-14 are some combination of A,B,C and X,Y,Z?
The 15th row is T^alpha
The Last 4 rows are the Helocentric components?

Could someone please define the columns: which is the X component of A, Y component of B, Z component of C, etc.

http://www.astrosurf.com/jephem/astro/ephemeris/et320buildVSOP_en.htm

The formula to use is :
et320img01.gif
Derivating with respect to time, we get the velocities :
et320img02.gif
Where :
- Ai, Bi, Ci are the terms in the BDL file.
- n is the number of terms given for a planet and a power of time (for example, n = 772 for Neptune, for variable X, T 0).
- T is in thousands of julian day from JD2000, T = (jd - JD2000) / 365250
 
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- X is the first column (the heliocentric x coordinate)- Y is the second column (the heliocentric y coordinate)- Z is the third column (the heliocentric z coordinate)- U is the fourth column (the heliocentric radial velocity)- V is the fifth column (the heliocentric tangential velocity in the x direction)- W is the sixth column (the heliocentric tangential velocity in the y direction)
 

Related to Understanding VSOP87 Column Names: BDL File Structure & Explanation

1. What is the purpose of the "BDL" file in the VSOP87 column names?

The "BDL" file is a data file that contains the coefficients for the VSOP87 mathematical model. These coefficients are used to calculate the positions of celestial bodies, such as planets, at a given time.

2. How are the column names in the VSOP87 file structured?

The column names in the VSOP87 file are structured in a specific format, consisting of a letter followed by a number. The letter represents the type of coefficient (position, velocity, etc.), and the number indicates the order in which the coefficient appears in the mathematical formula.

3. What does "VSOP87" stand for?

"VSOP87" stands for "Variations Séculaires des Orbites Planétaires" or "Secular Variations of Planetary Orbits." It is a mathematical model used to calculate the positions of planets in the solar system over a long period of time.

4. How do I interpret the values in the "BDL" file?

The values in the "BDL" file represent the coefficients for the VSOP87 model. These coefficients are used in the mathematical formula to calculate the positions of celestial bodies. The values can be interpreted as the strength and direction of the gravitational pull between the celestial bodies at a given time.

5. What is the significance of understanding the VSOP87 column names?

Understanding the VSOP87 column names is crucial for accurately using the mathematical model to calculate the positions of celestial bodies. It allows for proper interpretation of the values in the "BDL" file and ensures accurate calculations for scientific research and astronomical observations.

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