I am getting a little confused by which coordinates are reported by the mount. Moat other apps I work with give and expect J2000. SiTech gives JNow through ASCOM. Is there a way for the mount issue J2000 coordinates?
The J2000 coordinates are 20 years old, and obsolete as far as precision coordinates go. But there is not a J2020. There is JNOW! That is good, because it is always up to date and accurate.
SiTech, and all mounts and planetarium programs use JNOW AND J2000. However you do not need to worry or try to use a particular setting. It is all automatic when you tell the mount to go to a target. The only coordinates that are constant are the J2000 in the star catalogs, so your program then automatically calculates the JNOW and goes there.
When you click on a star or target in SiTech SkyView, the blue window that comes up shows both the JNOW and J2000 coordinates.
I use SharpCap to operate my QHY camera. Here is my concern: I
enter the J2000 coordinates of a target star. Click on J2000 and
GoTo. The mount slews to the target and reports the JNow
position. SharpCap has a built-in Platesolve feature and it
solves the image and reports what I think are J2000 coords. The
position from SiTech seems to differ from and the Platesolve are
slightly different. Can I be sure the difference is the
difference between J200 and JNow?
Or is the diff. within the accuracy limit of mount movement?
On 5/12/20 16:06, Don W wrote:
Hi Ned,
The J2000 coordinates are 20 years old, and obsolete as far as
precision coordinates go. But there is not a J2020. There is
JNOW! That is good, because it is always up to date and
accurate.
SiTech, and all mounts and planetarium programs use JNOW AND
J2000. However you do not need to worry or try to use a
particular setting. It is all automatic when you tell the mount
to go to a target. The only coordinates that are constant are
the J2000 in the star catalogs, so your program then
automatically calculates the JNOW and goes there.
When you click on a star or target in SiTech SkyView, the blue
window that comes up shows both the JNOW and J2000 coordinates.
All star catalogs are J2000 being used for platesolves. But the reported positions of platesolves are JNow. If you manually enter coordinates, you have to tell the program if they are JNow or J2000. Any time you call up a target by name, whether by SiTech or other program, you will go to the JNow coordinates.
The differences between J200 and JNow are small. They vary all around the sky. They are on the same order as the error in slewing to a new target. So they are nothing to worry about. Your targets will be in the FOV.
