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Using OnStep

Mount Orientation

When Reset or when an Alignment is started, OnStep always assumed the telescope mount is at the Home Position.

  • For Equatorial Mounts the Home Position is when the polar axis (RA axis) and telescope are pointing at a celestial pole.  For Northern Hemisphere users this is the North Celestial Pole NCP, roughly where Polaris is.  For Southern Hemisphere users it's the South Celestial Pole (SCP) that you want the polar axis and telescope pointing at. 
    • For a German Equatorial Mount (GEM) the counterweight should be down at |HA| = 6 hours.
    • For a Fork Mount (or similar) the forks should be left and right of the OTA at HA = 0 hours.
  • For an Alt/Az Mount (Dobsonians, etc.) home is a level base with the telescope pointed north and at the horizon (Alt = 0 degrees.)  This does not change for Southern Hemisphere users.
  • Tips:
    • Your mount might have a manual that describes the polar alignment procedure (specific to its polar finder perhaps) and if not you can find much helpful advice on the internet. Wikipedia also has a nice write-up on Polar Alignment.
    • If your mount doesn't have clutches and you need to use OnStep to move to the polar home position you can do so by enabling tracking or starting an Align (see below.)  Then use a guide control (N/S/E/W pad,) and a fast guide rate setting, to move the 'scope.  Finally press a [Home (Reset)] button to tell OnStep this is the Home Position and that you are "starting over."
    • The Home Position can be changed in the Config.h Axis settings sections.


The site information specifies the Latitude, Longitude, and UTC Offset (opposite of a Time Zone value.)  The Android App (Menu->Site Selection,) website, and ASCOM driver all have facilities to upload site information.  Sky Planetarium can be configured to send the site information when connecting.  Many 3rd party planetarium programs (etc.) can do the same.

  • Tip: Since OnStep remembers these settings site info. usually only needs to be updated if your observing location has changed since the last use.  When the observing location (site) does change the Android App can use GPS (if available) to automatically fill the site information for quick upload.


OnStep needs the current date and time to locate celestial coordinates and know where the limits of motion are. The date/time can be set up manually by commands or automatically retrieved from a real time clock (RTC), like the DS3234 (SPI), or DS3231 (I2C) at startup.

Note that the time sent into OnStep via the LX200 time-setting command must be your local mean (standard, aka LMT) time not adjusted for daylight time if that is in effect in your location. OnStep stores this to the RTC as UTC and uses the UTC offset to do that conversion so the UTC offset MUST BE SET FIRST. The UTC offset is the reverse sign of your (standard) time zone, for example, eastern standard time (EST) is -5.0 so the UTC offset is +5.0. Since the time in the RTC is kept in UTC there's no need to adjust for daylight time. Once the UTC is known, OnStep calculates the position of objects in the sky using that, the date and the longitude to get the local sidereal time (LST) which is the RA currently on the meridian. If your object lists do not show objects you know are in the sky or shows ones you know are not or you receive errors about objects beyond limits when you know that is plainly not true, the problem is likely that the time or location was set incorrectly.

The Android App has a button to set the date/time from the device's local time.  The website has a clock button that does the same. My Sky Planetarium can be configured to automatically send up the date/time whenever you connect. All these find out if daylight time is in effect from the device and perform the LMT conversion to standard time that OnStep requires automatically and thus do not need to ask you. Many 3rd party planetarium programs (etc.) can do the same.

However, the time you enter on the SHC is going to be the local (clock) time and, since it has no connection to the real world, it needs you to tell it whether that was a daylight savings time or not. The time the SHC then sends to OnStep is adjusted to be the LMT and then OnStep goes through the UTC conversion as described above before being stored. One warning though... when you go to the time setting menu on the SHC again the time may appear to be one hour out. This is because OnStep sends its time back to the SHC converted from UTC back to the standard time as it would have received it using the inverse of the UTC offset. However, the SHC can't do its 'standard' to 'daylight' conversion (if daylight is in effect) because the 'daylight' yes/no flag is not stored anywhere so there is no basis on which to know when to do the conversion and thus it just shows you the raw 'standard' time.


Now that OnStep has the correct site information and date/time you can start an Align, depending on your configuration, up to 9 stars may be used.  Generally its best to pick stars that are a bit away from the NCP or SCP and spread out across the sky.  For a GEM type mount its a good idea to have stars on both sides of the Meridian.

Android App/Smart Hand Controller:

In the Android App and SHC start an align then a list of suitable stars will be displayed to choose from. Pick a bright easily identified star and do a goto. If the mount is well constructed and polar aligned and OnStep was setup correctly the star should be in a wide field eyepiece of a small telescope or in your finder 'scope. Use the guide controls to center the star in the eyepiece. Then accept the alignment point.  For the Android App you need to then press and hold the "Align" button on the direction pad.  For the SHC simply press the center button.  If more alignment stars are required the list of stars will reappear and this sequence will repeat until done.

Sky Planetarium:

In Sky Planetarium the "ASCOM Telescope Control" dialog has has controls to initiate the alignment.  Again, pick bright easily identified star(s).  Do a goto (right-click map and select goto) to the first star.  Center the star in the "Control" dialog (Menu->Connections->Control...) then right-click on the map and select "Telescope accept align".  Repeat this process for each align star until done.

In addition to this functionality there is "Goto Assist" in Sky Planetarium which works with OnStep to do high precision n-star alignment.  Documentation for using this (and other alignment methods) is in Sky Planetarium's built-in help.

The OnStep SWS Website:

If you have access to the SWS Website it also provides the ability to set the date/time/location and perform a multi-star alignment working side-by-side with nearly any planetarium program with telescope control capability like Sky Safari, Stellarium, CdC, etc.

Other Planetarium Programs:

In lieu of using the SWS Website nearly any planetarium program with telescope control capability can still perform a Sync (basically a 1-Star Align) or simply enable Tracking to get going.

  • Tip:  When setting up the connection to OnStep in Sky Safari in "Settings/Telescope/Setup" use "Scope Type" Meade LX200 Classic and "Mount Type" matching your mount, also be sure the "Set Time & Location" option is disabled otherwise connecting can be very slow.


You're now ready to find objects. Since this example is for a 1-star align the accuracy will be somewhat less than what a 3-star align can do (for example) and you might want to do a goto and sync on a nearby bright star every now and then to help with pointing accuracy depending on how far you travel from location to location in the sky.

If using an Android tablet this is where I usually exit my App and start Sky Safari and connect for control from there.