Astroart Forum

Hello,

When an image is astrometric calibrated, a Nort/East indicator is visible in the image. I was wondering if this indicator can be expanded with direction of the sun - as an option. This is very useful for images of comets (and maybe other objects) -> see example below. Maybe it is available, but i didn't found it yet.
thanks
Erik.

Hello,
thank you for the suggestion.
It's not available, but it's easy to do. I've added it to the "todo" list.
Fabio.

Thanks for considering this and put on the list to do.
Erik.

it would be very useful to have this indicator and also the vector -V. To determine them, I usually use the ephemerides generated by JPL.
Ciao Adriano

Hello, the sun indicator was added in SP1:
viewtopic.php?f=2&t=417
what is the -V vector? May you give more information?

Thanks a lot, Fabio!
From the site of Horizon JPL (http://ssd.jpl.nasa.gov/sbdb.cgi) will be found in the ephemeris of each solar system body. As regards the comets, one can extract two important parameters:
- PsAng the position angles of the extended Sun->target radius vector ("PsAng") is an indicator of the comet's gas-tail orientation in the sky (if we add 180 ° you get the Sun vector indicating the position of the Sun)
- PsAMS the negative of the target's heliocentric velocity vector which is an indicator of dust-tail orientation.

Both the vectors are oriented as seen in the observer's plane-of-sky, measured CCW (east) from reference frame North Celestial Pole.

If it were also possible to insert the PsAMS vector (i.e. -V), we would have all the information in the images of the comets.

Thanks.
Adriano

Thanks, the problem with PsAMS is that it cannot be calculated on a given image: to calculate you need the orbital parameters of the comet, at the time of the exposure. This could be shown as a data of the Astroart star atlas, but not on a generic image like the other vector.
This is related to another problem: on new comets and minor planets the orbital parameters are valid for a limited time, so after some months when the MPCORB is updated that data is lost. It would be interesting to store in the FITS header the actual orbital parameters used on a given minor planet, using custom keywords.