I am a big fan of the SkyWatcher Star Adventurer and I think the graduation circles at its back are what set this tracker apart from the rest of the tracker on the market.
Too many people dismiss those graduation circles, originally there to help you polar align the mount, in favor of one of the many (allegedly) easier to use app.
I’d blame user laziness if only SkyWatcher would bother to describe their use in a way that would actually help. Instead, the user manual is laughable on this.
Never mind, you can read here my Ultimate Guide To The Use Of The Star Adventurer.
A less obvious way to use those obscure circles at the back of your unit is to measure changes in Right Ascension. Combine this with a way to measure changes in Declination, and you will not suffer for the lack of GoTo.
Right Ascension and Declination are global stellar coordinates, like Altitude and Azimuth… but better. Better because they do not depend on your position on Earth, nor from the date and time of the day.
Instead, Right Ascension (RA) and Declination (DEC) are referred with respect to Earth’s rotational axis, Earth’s equator, and the position of the Sun at the Vernal Equinox (March 31st). Neither of those changes in a human lifetime.
The scheme illustrating RA and DEC. From my recent video.
That’s great! We can pick one visible star, say, Vega, use an app like Stellarium or Sky Guide to know its RA and DEC. Then, use the same app to get RA and DEC for, say, the Ring Nebula (M57).
The Ring nebula is that little blue speck in this image taken with an equivalent focal length of 600mm on full frame.
This nebula is small and faint, meaning you cannot see on your camera live view and you need to use a long telephoto lens or telescope: the narrow field of view will not help to find the nebula.
But because we know the coordinates for both Vega and M57, and because we can surely see Vega, it is easy to compute the difference in RA and DEC between them and hop from Vega directly to M57.
And because RA and DEC do not change very quickly, we can compute all those coordinates differences while sitting comfortably at home, planning our imaging session.
But how do we measure changes in DEC if the Star Adventurer has no scale for that? Easy, we built one!
This is what we are going to craft.
What You Need
Here what you need:
A printer;
A CD or DVD or similar plastic disc.
A sheet of sandpaper, with medium grain;
A water hose in two parts, that screws on the tap;
A cutter;
Transparent scotch tape;
Brass ringlets and punch tool;
Print The Protractor
With this online generator for printing circular protractor, you can create one 4” 1/2 in size, with the double scale. The image below shows how to set the rest of the options.
Create a protractor 4” 1/2 in diameter, with precision of 1º. Select “Center Zero”, deselect “Circle Borders” and turn on the Inner Marks option.
Next, use a compass to draw a circle in between the two scales and cut along this circle. We will only use the inner scale.
Sand Down The CD/DVD/Plastic Disc
This is the rigid support we will tape the Protractor on. If we print the scale and mount it directly, night dew and condensation will make it saggy and useless.
Sand down the disc until you get a thickness of about 0.8/0.6 mm: this way you will be left with enough thread to mount your camera on the declination scale.
Center the protractor on the disc and tape it to it using transparent scotch tape: this will make the protractor moisture resistant and you will not smudge the printed scale.
Finally cut paper covering the hole of the disc.
Make The Mounting Assembly For A Snugger Fit
The hole of the disc is much larger than the screw to attach the camera to the declination bracket of the Star Adventurer: we need a better fit to remove lateral play.
Take the part of the water hose and cut it so to have a large base with a small step on top, with the step fitting into the part you screw on the tap.
Example of suitable water hoses for this job.
If you can find it in plastic, it will be easier to work the part, but if you find a similar one made of brass it should be fine.
You end up with a flat, small, disc having a step on a side: this step should snap firmly into the hole of our DVD.
To snap-in, the step must be 1.5cm in diameter and about 1 mm wide. The hole of the hose should be about 8 mm in diameter.
What remains from the hose: a large, flat base with a smaller step.
Finally, to further reduce the inner diameter of my amounting system so that it fits with little play on the screw of the declination deck, I used the punch tool and brass rings that are 6mm in diameter.
Brass rings with installing tool.
Putting All Together
Now, you should be able to have the mounting assembly to snap into the hole of the plastic disc that resembles something like this.
The finished mounting system for the protractor.
Your new declination scale will go between the deck and your camera.
To be able to quantify the change in declination, you have to tape a scale on the side of the declination deck.
I chose to have an 8cm long scale, with marks every 2mm.
Every mark corresponds to a change of 4-5 degrees in DEC, so you can have a precision of about 2º.
The scale to read changes in declination is taped on the side of the declination deck.
This should be enough to ensure your intended target is into the field of view of any instrument you could mount on the Star Adventurer.
Note that with the camera mounted, we can still rotate the protractor to align one of its marks with the 0 of the scale taped on the declination deck.
Friction, though, ensure the protractor rotates with the camera while using the fine adjustment knob.
In this video, I explain the whole concept and well as how to use RA and Dec to hop from a visible star to your intended target.
The whole concept is easy to grasp: to hop from a visible star to your target, you have to calculate the difference between the RA and DEC coordinates for the two objects and rotate the camera of the proper amount in RA and DEC.
Begin by positioning yourself behind the mount and by aligning the mount to the celestial pole. Then frame the visible star, so that it shows up at the center of your live view.
Now, compute the difference between the RA of your intended target and that of the visible star. If you have to move by a negative number of hours, you have to do a counterclockwise rotation of the mount. If you have to move by a positive number of hours, then rotate it clockwise.
This is true for the Northern hemisphere: reverse the rule if you are in the Southern hemisphere.
Depending on the difference in Declination and on how the camera is oriented, you have to rotate it clockwise or counterclockwise of the proper amount. This direction is easy to eyeball by looking at the sky.
When you do so, your target should be inside the field of view of your imaging instrument.
Let me know in the comments how this worked out for you!
Related Topics
How To Frame Any Target With Star Hopping
I recently wrote an extensive article explaining what Star Hopping is and how to do it to frame any target.
If you want to know more about Star Hopping and about how to use your newly made graduation circle for the declination of the Star Adventurer, read the guide I wrote for NightPixSky.
Learn More About Your Star Adventurer
Do you want to be a happy owner Of the Skywatcher Star Adventurer? If so, have a look at the Ultimate Guide To The Star Adventurer I wrote for NightSkyPix.
The mount is not difficult to use, but with a few extra tips and tricks, you will be able to get the most out of it with ease.