Manual Entering of RA/Dec Coordinates in the GoTo tool

[mgCatskills]

I've been searching for obscure objects that aren't in SharpCap's own catalogs, and often aren't in Stellarium. Sometime I can get the RA/DEC from SkySafari; sometimes I google the object, and find RA/Dec coordinates listed on a website. I've mastered how to enter them successfully into SharpCap, but often the location is near but not precisely where I'm trying to aim.

I presume this is because the coordinates are based on different dates.

Does SharpCap expect the coordinates to be J2000?

If the source is using a different date, is there a way to tell SharpCap the epoch so it will do the conversion? For example, I'm pretty sure I had one website list the coordinates as J2023.

Anyway, currently when I hand enter coordinates it's a crap shoot, and it's accurate less than half the time. It's pretty frustrating.

Regards,
Michael

[admin]

Hi Michael,

SharpCap expects all entered co-ordinates to be J2000, and will convert them to JNOW when sending them to the mount (if required). The same applies to co-ordinates in the built in and custom catalogs that SharpCap uses. Actually I just wrote this up as I was updating that part of the user manual the other day.

The theory behind that choice was that pretty much every where I looked for co-ordinates online, I was finding them in J2000, so it seemed to make sense to work that way.

To work around that in the current version of SharpCap, you would have to go to the python scripting level

Code: Select all

from SharpCap.Base import RADecPosition, Epoch
SharpCap.Mounts.SelectedMount.SlewTo(RADecPosition(12.00, 45.00, Epoch.JNOW))

That code will slew the mount to RA=12h, Dec=+45 in JNOW.

What sites have JNOW co-ordinates shown? If such sites are significant and commonly used then I may have to have an option for this in the GOTO page.

cheers,

Robin

[mgCatskills]

Robin,

I was copying RA/DEC coordinates from different sources, as I said. Many came from Sky Safari 7, as I was copying coordinates out of the object information.

All I'm sure about is that I copied the numbers accurately and SharpCap accepted them (though seems to round off decimal fractions). And they all had me pointing in the correct vicinity but not right on the target, despite platesolving.

I originally assumed that the coordinates Sky Safari lists are J2000, though my initial Google Search didn't definitively confirm that.

The search did lead me to settings under Precession & Nutation. This includes a "Use Current Epoch" toggle which defaults to on. There's also a Precession Epoch text box below it, which contains 2000.00. And an "include Nutation" toggle, also defaults to on. Plus some "other corrections".

When Use Current Epoch is toggled on, is that JNow? I suspect so, especially since a lot of mounts need that. If so, that would explain why I kept missing the target. If that's the case, then I guess I can turn off "Use Current Epoch" and assume the value would then convert to whatever date is in the text box, i.e. J2000 I could then enter the values into SharpCap. I'm guessing at this point, but will try to confirm.

Anyway, this stuff is mostly new to me. Frustrating that I wasted multiple observing opportunities. In a few cases it was obvious I was missing the target and was able to correct. In others, not obvious, either because the target was tiny (e.g. Neptune), or a galaxy in a cluster where I pointed to the wrong one.

Robin, thanks for clarifying this. I was dealing with uncertainties on both inputs and outputs. Now that you've confirmed I need J2000 as input, I can focus on getting appropriate outputs.

Michael

[admin]

Hi Michael,

glad that you are getting to grips with this. I suspect that the 'Current Epoch' switch in Sky Safari will mean using JNOW co-ordinates.

Note that for 2023, the maximum difference between J2000 and JNOW co-ordinates should be 8 minutes of arc in distance on the sky (the RA co-ordinate may vary by more than this if you are near the N/S celestial pole). That means that the target would be in view even if you had the wrong co-ordinate type unless you are working at a very narrow FOV. If you are missing the target by more than that, something else may be wrong.

cheers,

Robin