Re: Mach1 Unable to Find Home Position Suddenly

Roland Christen

The mount will always park according to the LST that the ASCOM driver calculates based on your time, date, location data. If it parks wrong, look at your LST number. Park2 and 3 are always 6 hours from LST. Park 1 , 4 and 5 are always at LST.

LST is your local sidereal time as calculated by the ASCOM driver from your local time that you input to the driver plus your time zone, your daylight savings setting, your longitude and of course your date.

When you slew to an object and it is off by 5 degrees, your inclination then is to move the mount 5 degrees to center the object and recal. When you do that you are actually shifting the entire sky including the overhead hour angle (LST or meridian line) by that same 5 degrees, and along with it all the park positions.

Is this a problem? Not really unless you specifically must have the mount park within a few arc seconds so that your rolloff roof clears the scope. Your time may be off for this session, but when you open up the next session it is not the exact time that determines where the sky objects are, it is the time difference. Therefore, objects will be centered even though the exact time is off as long as the time difference is correct.

This occurs dramatically twice a year when the time changes by 1 hour. If you forget to also change the daylight savings number by 1 hour then the time difference between the last session and the one after the 1 hour time change will be off by 1 hour. Then all sky objects will be 15 degrees in error, so then when you move the scope and recal or sync, you inadvertently also move the meridian line by 15 degrees and all parks accordingly. This is the most common effect that time has on the mount.


-----Original Message-----
From: Mikko Viljamaa <mikko.viljamaa@...>
To: main <>
Sent: Fri, Mar 20, 2020 5:11 pm
Subject: Re: [ap-gto] Mach1 Unable to Find Home Position Suddenly

Thanks Rolando, I have checked those a few times now. And if one of them would be incorrect, wouldn't the Mount always miss the position by the same 15 degrees or what not. Now the mount occasionally gets the park-3 correct. I keep checking but I'm pretty sure all the initial data is correct.

- Mikko

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