Since Daylight Saving Time (DST) is just a week away for most of the USA (you guys in Arizona and parts of Indiana are lucky :-), it bears reminding (and for new comers, warning) that the ASIAIR does not understand the concept of DST. They don't practice DST in China (heck, they have only a single time zone for the entire country!).

So, you need to go to your mount and turn off the DST setting. For some mounts that run on GPS and hell bent on setting the UTC offset to include the DST offset, you may need to also change the local time. The UTC Offset needs to be the UTC Offset for Winter (Standard) time and the local time on the mount should also show the time as if you are still in Winter (Standard) Time. If you don't know what the UTC Offset should be, go check Google now, so you will know what to set in your mounts a week from now.

If your don't do this, the coordinate system on ASIAIR and the coordinate system on the mount will be different, and the mount may not properly rotate during polar alignment. It may do an erroneous meridian flip when you perform a GOTO, not only pointing to the wrong location, or even drive your telescope into the tripod or pier. It will almost certainly also not perform Meridian flips (both automatic and manual) when a star crosses the Meridian.

The east-west position of a star in the sky is determined by its Right Ascension (RA). The east-west hour angle (HA) of your mount (the mechanical angle of the polar axis relative to the Meridian) is determined by the mount's motors. They are related by:

RA = LST - HA , where LST is the Local Sidereal Time.

The Local Sidereal Time can be computed from the Local Time, the Local Longitude and the Local UTC Offset.

Notice that a star crosses the meridian (when HA = 0) when the star's RA coincide with the Local Sidereal Time. This is how Longitude used to be determined accurately in the past by using a transit telescope located in Greenwich, England; everyone else checks when the same star crosses the meridian locally with their own transit instrument, and then figure out their local Longitude by comparing with the time the star crosses the meridian at Greenwich.

If Local time is wrong, or if UTC offset is wrong, or if Longitude is wrong, then the Local Sidereal Time is wrong. As a result, the HA (mount's angle) and RA (star's angle) will be off (usually by the 1 hour "Spring Forward" or "Fall Back").

Anyway, be prepared to make the corrections when DST arrives. Just remember that the ASIAIR assumes DST is always off at all times of the year, so you need to also turn off the DST on your mount, and for some mounts, you also need to adjust the time and UTC offset so that the mount thinks it is living in Winter (Standard) time.

Not all other countries changes to DST this coming weekend. Just make the above precautions when you switch to DST.

Chen

    Chen
    are you sure this works with all mounts? Last summer with my AVX I had DST and AAP was working fine

      And the time and gps should come from the tablet when you switch on AAP

        stevesp are you sure this works with all mounts?

        Try connecting to ASIAIR this Sunday morning. Regardless of the mount, Version 1.5.x of ASIAIR should now warn you to turn Daylight Saving Time (DST) off in the hand controller, if you had it set.

        My guess is that if you do not ever sync the ASIAIR to the Mount, you can ignore the warning, since the mount will be happily using its own Local Time, Longitude and the UTC offset to determine the correct Local Sidereal Time (LST). With a GPS, you only need the UTC and your longitude to determine the LST.

        However, if you ever use Sync To Mount to sync the Local Time from the ASIAIR app over to the Mount, that is where you can get into trouble if DST is turned on.

        I have personally never had a problem with Sync To Mount, but I have also always kept the DST of the mount off, and I never turn the GPS in my mount on. (Remember the old saw that a man with two watches is never sure what time it is?)

        Chen

          15 days later

          I found that I also have to modify the time on my tablet or phone to run at standard time. This is a huge pain in the @ for us stuck in daylight savings time.

          stevesp Yes, I agree with you........... After reading this original post and discussing this matter with Chen I was totally on board, and fully armed to make sure I had no problem come last Sunday, after the we once again put ourselves again through this now long ago needless practice of moving our clocks. For the love of God just put all of us in New England in the time zone we properly belong in, the Atlantic Time Zone, and keep us on DST all year. ( Sorry, I've digressed :-)) !! ).

          In any case come last Sunday evening as I was getting ready to start imaging I checked my GPS Ioptron 25CEMEC mount setting fully expecting to find that it had automatically adjusted from DST N. to Y. I was very surprise to see that it was still on DST N even though the clock itself had changed. I assumed then that I was all set, and would not have any problem as detailed in this post.

          After I did my PA, and then my first GO TO, it was clear however that I did have a problem. The mount would not point to the proper location. Bottom line I returned it to the Home Position, and then using the mount Hand Controller set the DST from N to Y. After that change and since then things are completely normal, and the GO TO function is perfect.

          I have no idea why this is the case with my mount since the details Chen described above make perfect sense. But for me no big deal. I will simply be mindful of this issue in the future, and keep hoping that sooner or latter we just stop this totally stupid practice of playing with our clocks. As if somehow by doing so we actually believe we really get an extra hour of daylight :-)) .

            The bottom line is the Local Sidereal Time (LST) of the mount has to be correct.

            If the LST is incorrect in either the Mount or in ASIAIR, then the location of the Meridian will be off. Auto Meridian Flips (and even manual Meridian Flips) will not work correctly.

            Check the LST on the hand controller. If it is correct, you are good to go since we can assume LST is correct in ASIAIR.

            If you cannot find LST on the hand controller, check the UTC and the Longitude on the hand controller. If those two are correct, then LST is correct.

            On iOS, UTC and Longitude are always correct as long as the GPS in the iPad is working. Therefore, ASIAIR's internal time should be independent of DST setting, since it should not even be using local time.

            It is trivial to confirm that the LST on ASIAIR is correct by pointing to a star that has not yet reached Meridian. Perform a fake AutoRun and see what ASIAIR reports as the time before the Meridian Flip. Then check with a planetary program for when the Meridian flip should occur.

            The problem occurs when the mount does not have the correct UTC and longitude. The mass market mounts don't like to confuse their customers, and usually use local time instead of UTC to set up time. That is where UTC offsets and Daylight Saving Time become the source of confusion.

            If the mount cannot establish its time, you have to push Date and Time information from the ASIAIR to the mount. When you do that, ASIAIR will be pushing a Local TIme to the mount, with the assumumption that DST on the mount is turned off.

            Longitude comes into play when you compute LST from UTC.

            Because ZWO is so hell bent not to make its user learn the concepts of astronomy, you don't find LST mentioned anywhere in the ASIAIR's GUI, even though LST is the first concept one learns in an introductory astronomy class.

            Fortunately, there are plenty of apps at the Apple App Store that can display LST. LST is also available in planetary programs. SkySafari displays it in the Date and Time setup under the Advanced tab. Any of those sourses wil confirm if the LST shown in the hand controller is correct.

            Again, check LST on the mount -- if it is accurate and if the mount is aligned ("star aligned" if the motors don't have absolute encoders), the mount should point to the correct location that ASIAIR commands the mount to point to.

            Chen

            3 months later

            I am thinking that these replies and solutions are related to the hand controller input to the mount. I have a 2 year old EQ6R Pro mount (no GPS) and never used the hand controller. I started with the EQDIR cable to laptop from the beginning. My understanding is that there is no information stored on the mount itself. Therefore, it would seem that any information on time would be coming from the phone through the ASIAIR PRO to the mount. I hit sync in AAP and it is still 1 hour off. Is there another fix? I never want to use the hand controller and bought just purchased the ASIAIR PRO because I thought I didn't need the hand controller. Please help. Can a time offset function not be added to the programs?

            4 months later

            You are kind of correct. The mount gets its info from the hand controller (if used, I usually don't) or the wireless controller, your device. Your device must not be on daylight savings time. Turn off network supplied time zone and use GTM offset.

            14 days later

            stevesp

            I use an iOptron Alt-Az Pro mount and a CEM40 . The Alt-Az built in gps will always use DST and it throws off the asiair slew-to.

            Its strange because it does this even if I do or do not 'sync to mount' . Once I change the DST off in the mount hand controller it solves the problem.

            On the CEM40, I just do not plug in the GPS and it works entirely off the AAP ...no problems there.

                2 months later

                I'm very confused with all of this.
                I have the AsiAir Plus, SW Neq6 Pro mount with v5 hand controler.

                Here is what I have been doing with no issues with AMF and GoTo's
                1) Turn mount on
                2) Input time and date (currently in Day light savings)
                3) do a rough 1 star alignment
                4) slew mount back to home position
                5) connect USB cable from AsiAir to Hand controller.
                6) Open AIRair App on Ipad/phone
                7) Connect mount in App & sync phone to mount
                8) Do a PA
                9) and you know the rest.....

                I have not touched the Ipad/phone time settings and my Goto's and Meridian flips have worked perfectly every time. The same goes when we have not been in Day light savings.... So what I'm I missing?

                One thing to note is after I do a sync from the App to Mount, the next time I use the mount and enter the time & date and setup for the night the day light saving is turned off in the Hand controller. I suspect this was done by the sync phone to mount.

                Cheers
                Wayne

                11 days later

                DST ended 7 Nov 2021 so it should be Off or No as you should have the same settings that you have in your Hand Controller.

                3 months later

                Please let me know if this response from Celestron (regarding the DST issue) is sufficient (I have a Celestron AVX mount)
                CELESTRON: "If you have the DST at Standard all you need to do is set up your correct timezone and everything will run smooth"
                Do I (can I) trust this???

                4 months later

                Hope this is helpful to CGX and CGXL users. When DST arrives I set the time in the Hand Controller to one hour behind DST, as if it never changed to DST. So when the time is 9pm in Summer, I set the time in the HC for 8pm. And I set the hand controller to Standard time. Bam! Works.

                a month later

                Very odd. I've used mine with an EQ6-R several times during DST without even thinking about this and it's worked every time. Note I connect directly to the USB port on the mount (the hand controller is still wrapped in it's shipping packaging). In other words, works fine as is.

                6 months later

                I hope I get an answer on this question. I get leavening the DST off and will leave it off. Do I leave the time setting itself the same also or go forward one hour like the clocks. ? HEM27EC mount.

                How does one go about turning off DST in the mount? I am using the AM5 mount with ASIAIR Plus (both using latest versions of software and firmware). When I open the AM5 app I do not see any setting to turn DST off!!

                w7ay

                How do you turn off DST on the AM5? The ASIAIR app tells you to turn it off, but gives you no clues how to do it. I went into the mount app and there is no way to change the time?

                How do I go about doing this?

                • jsg replied to this.

                    JohnKulczycki

                    Chen doesn't know, he doesn't use the AM5 mount. I have the same question. The newest version of ASIAIR (2.1) has this on the mount settings page:
                    "Please ensure that DST is disabled on HC, It's normal that the time on the mount is 1 hour earlier than your local time."

                    Yet I don't see any way to do this using the mount's app or the mount's hand controller (HC). Does anyone know what this is about and how to ensure that the ASIAIR Plus and the mount are communicating successfully in regard to guiding, tracking and the meridian flip?

                    Thanks!
                    Jerry