Plate Solving with APT

Last night I tried for the first time the “Point Craft” feature of APT (the Astro Photography Tool) and I was amazed!

First thing first, what is “plate solving” ? I guess the term “plate” comes from older times when astronomical images were taken using photographic “plates”. Today plate solving essentially means to analyze a digital astronomical image and figure out where exactly it points in the sky. This is done by analyzing the pattern of stars in the image and matching it with known star catalogues.

Why is this important / useful? There are various ways to ask your telescope mount to automatically point somewhere in the sky (Goto function). Each mount manufacturer has a way to achieve this, most commonly by firstly polar aligning the mount and then automatically pointing to a set of (1,2,3 or more) stars. The user then, for each star, makes a manual correction to point exactly to the star and the mount takes this correction into account, compensating for any alignment errors (no alignment is perfect!). Then the mount knows where the telescope is currently pointing and can “go to” where you ask it to point. Each mount manufacturer, depending on the mount type, has also other ways to achieve this that today range from assisting you to do near perfect polar alignment to self aligning mounts (however, no equatorial self aligning mount exists to my knowledge).

This alignment process is a way to tell the mount where exactly the telescope is pointing, so that it can “go to” more accurately to a target when you ask it to.  Plate solving comes to the rescue replacing the human action of looking through the finder and manually pointing to the star in order to tell the mount where the telescope is pointing. You take a picture and the software calculates exactly where the telescope is pointing automatically by matching the pattern of stars in the picture to known star catalogues. Back to why this is useful: The manual action required by the human to look through the eyepiece and provide feedback to the mount about where it is pointing just went away! You don’t even need to be close to the telescope… and yes, as the “All Sky late Solver” claims, you can now sell your finder 🙂 [unless you use it for guiding that is].

Plate solving is not something that appeared today, it rather exists for many years in professional and semi-professional astronomy software, but my personal feeling is that it has just entered a phase where the overall process, setup and the combination of needed software has become easy enough to be widely used. Judging by myself, I first tried this 2 days ago and was surprised about how straightforward it is… and I’m not even a “goto fanatic”.

I also have to say that I did not do an extensive search of all available software that supports this, I just recently learned that the APT (Astro Photography Tool – which I own and highly recommend!) supports this feature and figured I should try it!

Test session and setup

My setup is shown below

Test setup

Test setup

Test setup

I used my canon 100D camera (AC powered), Orion 80ED 80mm f/7.5 refractor and HEQ5 mount. For  connecting the mount to the computer I used a USB EQDIR cable and EQMOD with its ASCOM driver. I always use a gamepad controller to move the mount in this mode – seen in the picture (which I actually did not use at all!)

The software I used for controlling the mount and camera is APT (the Astro Photography Tool) which I highly value and recommend.

Setting up the software

Assuming you have installed APT, you need to download and install one of the plate solving software it is compatible with. The APT manual describes which possibilities exist, I used All Sky late Solver (ASPS), which does a so called “blind solving”, not requiring prior knowledge on where the mount it roughly pointing.

After installing and starting ASPS, the software guides you through the process of downloading the necessary star maps by asking some basic information on the combinations of telescopes / cameras that you intent to use. This is required in order to download only the necessary star maps.

ASPS downloading star maps

ASPS downloading star maps

As shown in the figure above, you need to enter the focal length of your telescope (600mm for my case) and the sensor size of your camera (22x15mm roughly for the canon 100D). Then the software automatically selects the necessary star maps and you can download and install them by clicking a button. I guess you can repeat the process for other telescope/camera combinations in order to download all the maps you will eventually need. The plate solving software is now ready to be used with APT.

When you start APT, you must configure it to point to the ASPS directory (by clicking the settings option in the point craft panel)

pointcraft settings

pointcraft settings

Telescope / mount setup

The mount needs to be polar aligned (the more accurate the better) and the telescope in its “home” position, pointing to the north (or south depending on your location on planet earth) celestial pole.

Starting APT and connecting to the equipment

Starting APT and connecting to your camera and telescope should be straightforward. One point is that since APT will be connected to the mount if you want to use other software that connects to the mount as well (such as your planetarium software or your auto guiding software) you need to connect using the POTH ASCOM driver, which acts as a proxy to your actual mount connection.

POTH ASCOM driver

POTH ASCOM driver

POTH ASCOM driver

POTH ASCOM driver setup

When you select POTH and click properties, you can choose and setup from there your ASCOM telescope driver (which in my case is the EQMOD HEQ5/6). Then by clicking OK, APT is connected to the mount. Be sure that you have correctly setup the ASCOM HEQ5/6 driver by entering your location, ports, etc.

Using APT Point Craft (Plate Solving)

Now that you are connected to your telescope mount you can ask APT to go-to an object, by clicking the “Objects” which is available in the Point Craft panel  (shown below) or next to the Point Craft button, in the gear tab..

pointcraft

pointcraft

APT Objects

APT Objects

You can also use your planetarium program to “go to” somewhere or just use it to browse available objects and then choose the object from APT.

Starry night

Starry night

I used Starry night as my planetarium program without connecting it to the mount. I browsed the objects and then used APT to select the object I wanted to go to.

First thing first, I took a 5 second image at iso 1600 with the telescope pointing to its “home” location (north celestial pole) using the “Shoot” option and clicked “blind” button in the point craft menu. On my (really) slow laptop this tool about 40 seconds until a “success” and the RA and DEC coordinates appeared.(I reproduced the image below while writing this, by loading the image again to APT and asking it to plate solve it)

initial plate solving

initial plate solving

I then clicked “sync” which updates the actual pointing coordinates of the telescope to the mount.

I then played around using this exciting feature and “plate solved” several 10 second images. I then asked APT to point me to andromeda and took a 10 second image to see where the telescope was pointing.

Andromeda

Andromeda

Spot on.

I then played around asking APT to point me to various objects, then taking an image and from time to time plate solving it and “syncing” with the mount (informing the mount where the telescope is pointing exactly).

OWL Cluster

OWL Cluster

ngc7789

ngc7789

Little Dumbell

Little Dumbell

double cluster

double cluster

how much fun!

As a final test, I tried the “goto++” function to point to M33.

This function repeats the process of “pointing, solving, syncing” completely automtically until the telescope points precisely to the target. Below is the result on M33.

M33 with goto++

M33 with goto++

I hate to admit it, but sometimes I had spent a considerable amount of time aligning the mount or manually trying to find my targets. Now I am able to do this in under a minute without even looking through the finder. This is so exciting!!