EQMOD incorrect time

[Stepe]

Hello

I am connecting my HEQ5 mount to a Windows10 laptop using EQMOD Eqdir LynxAstro cable. Looks like it works OK but the EQMOD control panel is showing a wrong clock time - 20mins ahead. The observatory coords are correct and while I was using a connection through the handcontrol of course I had to set the time myself so it came out correct. I have tried to unplug and re-plug the cable and also use another Eqdir cable but... nothing, always 20 mis ahead. Somebody has a suggestion on how to change the time displayed or why this happens?Thank you

[MartinB]

Interesting, I will check my own setup.  I guess this makes sense since the stars don't move in 1 hour jumps!  So the the true celestial time based on your coordinates will differ from the time on your watch.

[fifeskies]

Yes , true time will be 4 mins per degree different from your time zone prime meridian.

My location being just over 3 degrees West of the meridian I am about 13 mins different time from the zone clocks as far as the stars are concerned.

 

When you enter your co-ordinates into a hand controller it internally compensates the mount for the correction for zone time, allowing you to use the time from clocks watches etc to enter time data as this is far easier.

The hand controller simply asks for the time zone the entered time refers to (and for daylight saving confirmation when the 1 hour change is active).

 

 

Edited October 14, 2020 by fifeskies

[Stepe]

Uhmm fifeskies and MartinB, thank you for yr replies but... I am losing a few points here... I don't understand the prime meridian of the time zone thing... need to check my geographic knowledges.  What I understand however is that the hour displayed in the EQMOD panel is ...just a display that won't affect how EQMOD itself works with the mount (alignment, limits, park positions, planetarium interaction, game controller, etc)

[Stepe]

From EQMOD documentation:

EQASCOM shows the Local Sidereal Time and users should not be concerned that the value displayed does not match the PC time.

[fifeskies]

Stepe

I will try to illustrate

 

Taking the UK as an example , the Greenwich meridian passes through , you guessed it Greenwich.

In a much simplified view , the sun will be overhead at Greenwich at noon GMT.

(edit: I should really say due South not overhead, but it will be as near overhead as its going to get 🧐 )

 

I live just over 3 degrees West, when my UK clock tells me its midday noon MY sun is not overhead yet , it will not be overhead for another 13 minutes.

(and not overhead in East coast USA for another 5 hours).

Because the world only has 24 time zones , the actual sidereal time anywhere will be ahead or behind the time zone depending if it is East or West of the local meridian.

If my mount used just GMT to aim it would be aiming in the wrong place

(trying overhead for the sun in the above example when it is still off to the East of overhead from where I am, so the system needs to use the local sidereal time to find objects)

(Do NOT look at or aim at the Sun though a telescope of course unless it is designed for solar).

 

Hope that helps

Edited October 14, 2020 by fifeskies

[chrisshillito]

On 14/10/2020 at 14:18, Stepe said:

What I understand however is that the hour displayed in the EQMOD panel is ...just a display that won't affect how EQMOD itself works with the mount (alignment, limits, park positions, planetarium interaction, game controller, etc)

The "time" EQMOD displays is the the Local Sidereal Time. This is effectively the instantaneous Right Ascension value associated with the meridian line. LST is an essential parameter that EQMOD uses when calculating how to move the mount in order to bring it onto any celestial target. You are correct that LST doesn't have any bearing on park positions. Your planetarium will probably display its own LST calculation somewhere and this should be the same as EQMOD - if it isn't then there maybe some difference in observing site data between the planetarium and EQMOD which should be "fixed".

Chris.

[Stepe]

Now I begin to understand what you mean... fifesky and chris thank you for taking the time to explain and yes chris, Stellarium must make its own calculations for LST somewhere while it displays the watch time.