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Basically AlpacaScope is a lot like the SCC SkyFi and Sequence Generator Pro's WiFi Scope.

Unlike the SkyFi, there is no special device you have to buy to control your telescope; you can just use your Windows, Mac or Linux computer. AlpacaScope controls your telescope via ASCOM Alpaca which is an open source and open standard for astronomy software.

If your telescope does not yet support Alpaca, there is good news: you can use ASCOM Remote Server to bridge Alpaca to the older Windows-only ASCOM platform.


Download the latest binary appropriate for your hardware/OS.

Note there are now CLI and GUI versions of AlpacaScope! Please download the version which works for you. :) Please note that the GUI version requires an OpenGL video card/driver.


[](Step-by-setup instructions to use AlpacaScope with SkySafari).

My setup looks like this:

Celestron Evolution <-> CWPI <-> ASCOM <-> ASCOM Remote <-> AlpacaScope <-> SkySafari
             Focuser  <-'           `-> Sharp Cap
                                     `-> ZWO Camera

Basically, just download the binary for your system (easist to run on the same Windows box as ASCOM & the ASCOM Remote Server) and run it. It will automatically find the ASCOM Remote Server running on your network and connect to it.

Configure SkySafari or other remote control software to connect to AlpacaScope on port 4030 using the Celestron NexStar (I use the NexStar/Advanced GT) or Meade LX200 GPS protocol. AlpacaScope supports both, but defaults to NexStar.

AlpacaScope supports the "Auto-Detect SkyFi" feature in SkySafari so you should not need to enter the IP address of your computer running AlpacaScope.

Graphical User Interface

Hopefully the above is pretty self-explainatory. In general, the defaults (other than the mount type) should work 99% of the time and you can just press Start AlpacaScope Services. This will then:

  • If 'Auto Discover Alpaca Mount' is enabled, it will try to find it on your local network
  • Attempt to connect to ASCOM Remote or your Alpaca mount directly
  • Start SkyFi auto-discovery for SkySafari
  • Listen for new connections on the ListenIP/ListenPort

Command Line Flags

AlpacaScope supports a number of optional CLI options. For a full list use the --help flag.

  • --help Built in help
  • --alpaca-host Manually set the FQDN or IP address of the host running ASCOM Remote Server
  • --alpaca-port Specify a custom TCP Port where ASCOM Remote Server is listening
  • --listen-ip Manually set an IP address to listen on
  • --listen-port Override the default port of 4030 to listen on
  • --mount-type Specify your mount type: altaz, eqn, or eqs. altaz is the default.
  • --mode Choose between nexstar and lx200 protocols. nexstar is the default.
  • --debug Print debugging information


TL;DR: I have a Celestron Evolution EdgeHD 800 and I'd like to be able to control it via SkySafari.

Unfortunately, the WiFi on the Evolution mount is known to be a bit flakey and it's annoying when it drops out and you have to exit the app, reconnect to WiFi, restart the app, and re-connect to the telescope.

So I decided to create this little application which allows me to control the telescope via CWPI which runs on the PC I have connected to the telescope via USB. Of course, SkySafari can't talk directly to CWPI. CWPI supports ASCOM but that only allows IPC via Windows COM which doesn't even support talking to programs on other computers (or my iPad).

But then in 2019, ASCOM introduced Alpaca which via ASCOM Remote Server exposes the ASCOM API via REST. Of course, SkySafari doesn't support this (yet) so I decided to write a service which emulates a telescope SkySafari supports and talks to Alpaca Remote Server. The result is that SkySafari can now control my Celestron Evolution mount, or any mount that supports the ASCOM or Alpaca standards.


Does this only work with NexStar and LX200 series telescopes?

No! AlpacaScope works with any telescope / mount supported by Alpaca or ASCOM. The LX200 and NexStar protocols are only for communicating with software like SkySafari or StarryNight. You can even use the LX200 protocol with your Celestron scope if you want because AlpacaScope does all the translating between the different protocols.

Should I use NexStar or LX200 protocol?

Short version:

No matter what kind of telescope you have, you probably want to pick NexStar in AlpacaScope. In SkySafari and StarryNight, you should choose Celestron NexStar/Advanced GT.

Longer story:

The protocol spec for Celestron NexStar is more consistently implimented in my experience and users report a lot more issues with LX200. So I would definitely recommend people try NexStar before LX200. Yes, this even means people with a Meade LX200 series telescope should probably choose NexStar! Yes, that is very confusing but trust me. :)

That said, I understand there are cases where you might need to use LX200 and I do my very best to support it. If you experience any compatibility issues, please let me know so I can try to either fix the bug in my code or develop a work-around for poorly behaved clients.

What do I need at minimum?

  1. A telescope mount with an ASCOM or Alpaca driver.
  2. The ASCOM/Alpaca driver configured on a computer.
  3. If your mount only has an ASCOM driver, you will need ASCOM Remote Server installed, configured & running
  4. AlpacaScope installed and running
  5. Some kind astronomy software which talks the Meade LX200 or Celestron NexStar protocols (SkySafari, etc)

How do I configure AlpacaScope and ASCOM Remote Server?

This document provides step-by-step instructions to configure everything.

Does this support SkySafari on Mac, iPad, Android, etc?

Yes, this supports all versions of SkySafari which allow for controlling telescopes. Typically this is SkySafari Plus and Pro.

What about other astronomy software?

Yep, anything that can do Celestron NexStar or LX200 protocols over TCP/IP should work.

Why do I get a virus warning for alpacascope?

Unfortunately, this is a known issue with GoLang programs. A few anti-virus programs incorrectly flag Go programs as a virus because Go binaries "look funny". Here is another Go program with the same issue. I've scanned AlpacaScope with 71 different AV engines via Google VirusTotal and as you can see, only 2 AV products said it was suspicious.

For the record, I build all the release binaries on a Mac- so the chances of a Windows virus infecting the binaries is pretty much zero.

Windows says AlpacaScope was published by an unknown author?

Yes, I haven't yet paid Microsoft a fee so you will get this warning. If you have downloaded the AlpacaScope binary from it should be safe, but if you want to be extra careful you can verify the GPG signature I include with every release.

What features work with SkySafari?

  • Manual slewing
  • Controlling slew speed
  • Goto a target
  • Align on target
  • Set time and location of observing site

I'm using something other than SkySafari and it has more feature than that?

AlpacaScope can support any command supported by both the Alpaca API and the LX200/NexStar command sets. If you have a need for another command, please open a feature request on GitHub.

What about focuser, filter wheel, etc support?

The NexStar and LX200 protocols don't support that.

Does AlpacaScope support INDI?

No it doesn't. There's probably no reason it can't support INDI since I believe it is cross-platform, but I haven't looked into it yet.

Does AlpacaScope need to run on the same computer as Alpaca or ASCOM Remote?

No, but that is probably the most common solution. AlpacaScope just needs to be able to talk to the ASCOM Remote Server running on the same computer as the ASCOM driver connected to your telescope mount.

My telescope mount has an Alpaca driver. Can I use that instead of going through ASCOM Remote?

Yes! Over time I expect more telescope mounts to have native Alpaca support and not require using ASCOM and ASCOM Remote.

For the LX200 protocol should I select "LX200 Classic" or "LX200 GPS"?

SkySafari users should use "LX200 GPS/ACF LX600" as there seems to be at least one issue with using LX200 Classic mode.

For the NexStar protocol, which scope type should I select?

SkySafari users should probably use "Celestron NexStar/Advanced GT" as that's what I've done most of my testing.

How to build on Windows?

If you wish to build your own binary on Windows, you'll need to do:

  1. Install GoLang for Windows by following these instructions.
  2. Install GNU Make for Windows/Git by following these instructions
  3. Install TDC GCC.
  4. Clone this repoistory onto your computer using Git or just downloading the Zip file from Github.
  5. Using the Git shell (installed in Step #1), from inside of the AlpacaScope source tree, run make windows-gui or make windows-release to build a binary.

How to build on Linux, OSX, etc?

  1. Install GoLang for your OS.
  2. Make sure you have GNU Make installed. BSD Make will not work out of the box. If you don't want to install GNU Make, you'll have to run the go build command manually.
  3. Clone this repoistory onto your computer using Git or just downloading the Zip file from Github.
  4. Run make (or gmake) to build a binary for your OS.
  5. Run make help to get a list of other OS targets you can build. Note that GoLang makes cross-compiling easy so no problems building a Windows binary on Linux or MacOS binary on a RaspberryPi. :)

What is the purpose of the --mount-type flag/Mount Type GUI feature?

The Celestron NexStar protocol supports the concept of different tracking modes: AltAz, EQ North, EQ South and Off. Typically this would be used with a AltAz fork mount which can optionally have a wedge. The result is the mount must be told to change it's tracking mode.

However, Alpaca/ASCOM does not support this- it only allows you to turn on & off tracking. Hence, AlpacaScope allows you to specify the mount type at startup, and then when SkySafari/etc queries the current tracking mode it will get the correct answer.