Coordinate systems

[YahooGroup]

This is a transfered topic from the ASA Yahoo Group.

 

Posted By: georgecarey47 Fri May 3, 2013 1:54 pm

I have never been able to get Autoslew, Maxim and Cartes du Ciel to give
consistent coordinates for objects and where the scope is pointing.
If I set all three to J2000 there is a big offset. This image shows Maxim when I
have slewed and synced on Beta Lyr.

http://geoastro.co.uk/may2013/coords.jpg

Autoslew says 18 50 3.38 and +33 21 52
The star coordinates are 18 50 05 and +33 21 46
To get the mouse position coordinates the same as Autoslew I have to move
slightly away from the star.
The circle that indicates where the scope is pointing is way off to the side.

If I set Autoslew to 'Real' and Maxim to J2000 the agreement is closer but not
spot on.

Can someone please give a guide on how to get everything in agreement?

George

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Posted By: jbaj82 Fri May 3, 2013 2:04 pm

I have the same issue. Most of the time I send slew commands to Autoslew over
Ascom in J2000, while Autoslew indicates "real". That way I get the best
pointing results.

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Posted By: nischangde Fri May 3, 2013 3:18 pm

Hi George,

the same problem happened to me, running Autoslew, Maximdl and Guide 8. Doing
all slews (except "Dither via mount") from Guide, I found out the most accurate
setting is to use "Real", called "Mean of Date" or (Mean) in Guide.

cs
Martin

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Posted By: georgecarey47 Fri May 3, 2013 4:54 pm

I think I may have cracked it.

Step 1 Upgrade to a newer version of Cartes du Ciel
Step 2 Set Autoslew to 'Real'
Step 3 Set Cartes du Ciel to 'Apparent, (true equator, equinox and epoch of the
date)

I now get everything displaying the same coordinates - see here
http://geoastro.co.uk/may2013/screen.jpg

Now I have to see if I can get asteroid and comet coordinates in the same form!

George

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Posted By: georgecarey47  Sun May 5, 2013 1:09 am

I had the chance to try a few tests tonight. With Cartes du Ciel and Autoslew
both set to 'Real' coordinates pointing was excellent. I have amended my
spreadsheet for making object lists so that it will now extract J2000
coordinates from the ephemeris.
The coordinates in the pointing list are set to J2000.
When Autoslew runs through the object list it converts the J2000 coordinates to
Real. This image was the first slew to comet Panstarrs at 10:30pm (BST). The
slew started at the other side of the sky in Hercules.
http://geoastro.co.uk/may2013/test.jpg
That is close enough for me!

The object list looks like this:

8
*****************************
Object Number 1
Object Name :21:00 C/2011 L4
Epoch: 2000
RA : 0.0824444444444444
DE : 70.4908333333333
*****************************
Object Number 2
Object Name :21:30 C/2011 L4
Epoch: 2000
RA : 0.0817777777777778
DE : 70.5083333333333
*****************************
Object Number 3
Object Name :22:00 C/2011 L4
Epoch: 2000
RA : 0.0811388888888889
DE : 70.5255555555556
*****************************
Object Number 4
Object Name :22:30 C/2011 L4
Epoch: 2000
RA : 0.0804722222222222
DE : 70.5430555555556
*****************************
Object Number 5
Object Name :23:00 C/2011 L4
Epoch: 2000
RA : 0.0798333333333333
DE : 70.5605555555556
*****************************
Object Number 6
Object Name :23:30 C/2011 L4
Epoch: 2000
RA : 0.0791666666666667
DE : 70.5777777777778
*****************************
Object Number 7
Object Name :00:00 C/2011 L4
Epoch: 2000
RA : 0.0785
DE : 70.5952777777778
*****************************
Object Number 8
Object Name :00:30 C/2011 L4
Epoch: 2000
RA : 0.0778333333333333
DE : 70.6127777777778


I have set the object 'name' as the time and the comet identification which
shows up neatly in the Autoslew window.

George