Problem in generating ephemeris data

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In summary: Expert SummarizerIn summary, the speaker is having trouble calculating the position of celestial bodies (specifically Pluto and the Moon) in the VSOP87C frame. They have coordinates in two different frames, with Pluto being in the J2000 frame and the Moon being in the ELP82 frame. The speaker needs help with the math to convert all coordinates to the VSOP87C frame and perform calculations. The suggested approach is to first convert all coordinates to the J2000 frame, apply light time corrections, and then rotate them to the mean equinox and ecliptic of date using a rotation matrix. Further assistance can be sought from other scientists or relevant literature.
  • #1
cptolemy
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Hi,

I' having an hard time with the following issue.

I've made some routines to calculate the ephemeris from Earth to Neptune with VSOP87C - referred to the mean equinox and ecliptic of date, I supose.
So, the data I receive, is already precessed to the mean equator and ecliptic of any date.

Then, I wrote the code for calculating the position of Pluto, with Pluto95 theory - these coordinates are referred to the mean equinox and ecliptic of J2000 however.

To complicate things, VSOP87 is not in the FK5 frame... And according to Meeus, we must make first the corrections of light time before converting them to FK5.

So my question is: how do get the position of Pluto into the VSOP87 frame (mean equinox and ecliptic of date, no FK5) to perform the calculations?

The same thing happens with the Moon - with ELP82 theory.

I'm really stuck... And I need help with the math in this one...

Kind regards,

CPtolemy
 
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  • #2


Dear CPtolemy,

Thank you for sharing your issue with us. It seems like you have a complex problem at hand, but fear not, there are several ways to approach this.

Firstly, when dealing with celestial bodies, it is important to have a consistent frame of reference. In this case, you have VSOP87C coordinates referred to the mean equinox and ecliptic of date, and Pluto95 coordinates referred to the mean equinox and ecliptic of J2000. To simplify the problem, I would suggest converting all coordinates to the mean equinox and ecliptic of J2000. This can be done by using the appropriate precession and nutation equations.

Once all coordinates are in the same frame, you can then apply the light time corrections as mentioned by Meeus. This will give you the correct positions of the celestial bodies in the J2000 frame.

To convert these coordinates to the VSOP87C frame, you will need to use a rotation matrix. This matrix will take the coordinates from the J2000 frame and rotate them to the mean equinox and ecliptic of date. You can find the necessary equations and values for this rotation in Meeus' book "Astronomical Algorithms".

Once you have the coordinates in the VSOP87C frame, you can then perform your calculations as desired.

As for the Moon, the same approach can be used. Convert the coordinates to the J2000 frame, apply light time corrections, and then rotate them to the mean equinox and ecliptic of date using the appropriate rotation matrix.

I hope this helps you with your calculations. If you need further assistance with the math, do not hesitate to reach out to other scientists or consult relevant literature. Good luck with your research!
 

1. What is ephemeris data and why is it important?

Ephemeris data is a set of astronomical information that includes the position, velocity, and other relevant parameters of celestial objects such as planets, moons, and comets. It is important because it allows scientists to accurately predict the movements and positions of these objects in space and time, which is essential for various scientific and navigational purposes.

2. What are some common problems encountered in generating ephemeris data?

One of the most common problems is the accuracy of the data. Small errors in measurement or calculation can lead to significant differences in the predicted positions of celestial objects. Another issue is the availability of data, as ephemeris information for certain objects may be limited or unavailable. Additionally, the complexity of the mathematical models used to generate ephemeris data can also present challenges.

3. How is ephemeris data generated?

Ephemeris data is generated through a combination of observations and calculations. Astronomers use telescopes and other instruments to observe the positions of celestial objects at specific times. This data is then input into mathematical models that take into account factors such as gravitational forces, orbital mechanics, and other celestial phenomena to predict the object's future positions.

4. What are some applications of ephemeris data?

Ephemeris data has a wide range of applications, including space exploration, satellite navigation, and astronomical research. It is also used in fields such as astrology and horology, as well as for predicting the occurrence of celestial events such as eclipses and meteor showers.

5. How accurate is ephemeris data?

The accuracy of ephemeris data depends on various factors, such as the quality of the observations, the complexity of the mathematical models used, and the time span for which the data is being predicted. Generally, ephemeris data is considered to be highly accurate for short-term predictions, but its accuracy decreases over longer time periods due to the influence of external factors such as gravitational perturbations from other celestial objects.

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