Galileo's Finger - an Open Source Astronomy Learning Tool




About: Being an engineering student, I enjoy being challenged to solve problems in the most innovative way possible, or even just coming up with fun ideas for projects.


Given the opportunity to use one of the Intel Galileo boards, we wanted to build something that would honour Galileo's memory and pay tribute to his discoveries. What better way than to do something related to his primary focus - astronomy.

Being an avid astronomer, and loving being able to look up into the night sky and know what star or planet I'm looking at, I thought a cheap, accurate laser pointer would be perfect.

With the right idea in mind, and three weeks in which to do it, my partner and I set off coding and building.

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Step 1: BOM

This is what we needed (software side included) to build our model:


• Soldering iron
• Hot glue gun
• Drill and appropriate bits
• Saw
• Pencil


• Intel Galileo (Any micro will work – you just need serial communications and 4 output pins)
• 2 x Stepper Motors (we used Nema 17s)
• 2 x Stepper motor controllers (we used Easy Driver v4.4)
• Veroboard/Breadboard
• Some headers to mount the motor controllers
• Wires for connecting
• Ball bearings (we used parts from an old printer and harddrive - see pictures)
• Elastic bands
• Solder
• Laser pointer (please be careful with this)
• AA battery pack(or anything that can provide a steady 3V - NOT the arduino)
• Wood


• Arduino IDE
• Python 3.3
• PySerial
• PyEphem
• Stellarium

Step 2: Create the Circuit Board

You can use a breadboard, veroboard, or even print a PCB if you have the time and resources. The circuit diagram is below.

  1. Connect MS1, MS2 and the GROUND (next to step) on both boards to GROUND on the ARDUINO.
  2. Connect M+ and GND (on the PWR IN) on both boards to the 12V power supply for the motor.
  3. Connect DIR on easyDriver 1 to Arduino pin 4.
  4. Connect STEP on easyDriver 1 to Arduino pin 5.
  5. Connect DIR on easyDriver 2 to Arduino pin 6.
  6. Connect STEP on easyDriver 2 to Arduino pin 7.
  7. Connect each motor to its own easyDriver, paying attention to which coil is which.

Step 3: Software

You will need to download and install the following.

  1. Arduino
  2. Python
    • (we used python 3.3)
    • pySerial - choose the one that's correct for your version of python
    • phEphem - again, watch python version you are using
  3. Stellarium

TelescopeMotorController (both arduino code and python code) - Github Source

Note: A special thanks to Sven Steinbauer (GitHub) for the python code (pyscope)

A special note here: You will need to make some changes to the python code. Specifically,

  1. The com port used (this is almost guaranteed)
  2. The city you are in (or at least your lat/long)
  3. The degrees on the stepper motor
  4. The gearing ratio

All of these are commented as to where you might need to change them

Step 4: Construction

This part is fairly simple. You just need to be able to move the laser on 2 axes. The truth is almost anything will work, and because we did not make out model from standard parts (mostly e-Waste and some cheap wood), it's hard to be specific about the build. I have attached the pictures of our model below, so you can get an idea of what to build. In short:

  • There are 5 wooden pieces
    • 2 wheels for X-axis/azimuth (we used 2 instead of 1 for accuracy.)
    • a mount for the X-axis/azimuth bearing (harddrive bearing)
    • a mount for the Y-axis/altitude bearing
    • a base to mount everything on
  • Once the wooden pieces have been made, cut out the holes to place the bearings, and fix the bearings down
  • Attach the laser to the altitude bearing. We had to remove the batteries from the laser and mount them separately in a battery clip - the bearing would not support its entire weight)
  • Stick it all together! (just make sure the parts that can move, still move!)

Step 5: Completed Product

Enjoy your low cost, open source starfinder!

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33 Discussions


2 years ago

can be used as aiming/ star tracking for telescope, yes?

1 reply

Reply 2 years ago

Hi Dr Luthor

Yes, it can. One of the lecturers in our astronomy department uses something similar to calibrate her telescope.


2 years ago

can this run on a mac?


3 years ago

acredito que faltam detalhes sobre o telescopio... a parte mecanica logicae cnc e facil.

onde encontro dados sobre o telescópio?

This qualifies as an outdoor laser display. I HIGHLY discourage anyone from building and using this outdoors in the USA. The FAA has pulled the document(s) pertaining to outdoor laser displays from their website. They just pulled them yesterday with no explanation. You must call them and tell them when and where you will be running this in order to be granted a variance. If you are caught, we are talking thousands of dollars in fines and possibly jail or even prison time. But now that they have deleted the legal documents, I have no idea what they might do to you. The beam can be seen for miles and is like a big arrow pointing right at you, making you very easy to find. I want everyone out there to know this. We are living in a very messed up world right now.

5 replies

Thank you, this is very valid. Here in SA though there's less of a restriction, which is nice. I have added a warning, thank you for your input.


Reply 4 years ago on Introduction

I'd still love to see a picture of what it looks like with the laser operating. Mine works well enough with a simple pointer but the laser would be awesome.

Perhaps, not so messed up... if the documents were pulled. When I first read this, I had an image of looking out over the night sky and seeing amateur astronomers with galileo's Fingers pointing up at various stellar objects as if saying, night sky lovers live here, only to be replaced by an image of Uncle Sam and his finger smashing mallet crushing my blissful scene.

I then had a few thoughts; 1: Perhaps a lower strength laser, that would maybe make a slightly visible but lower powered finger, or 2: using a red-dot pointer, like those on telescopes which are small, virtual pointing devices that don't actually emit a beam, or do, but only visible as a pointing scope, and obviously legal, or 3: use a pointing stick with crosshairs that one could merely sight along to see where it's pointing.

Obviously this device was meant to 'virtually' touch the stellar object where one would see it with the naked eye, or meant to be attached to a telescope to give one the superior locating power found in more expensive telescopes. Still, with the restriction, I think it would bear an in depth examination, and possible contact with the FCC to discover the exact limitations required to be legal with such a device as we know laser pointers are used in classrooms, and as cat toys and if it was a problem pointing them into the sky, most of use would have been arrested by now. I think we'd just need a laser, that would dissipate the light such that it spread and the beam dissipated below a certain altitude.

Of course, if we're going to get paranoid, any system, no matter how little or no power existed in the finger, could be built to swap out a more efficient and powerful device for ulterior purposes. And, I would ultimately like to believe that Uncle is not out to destroy the hopes of amateur scientists, and expect that like powered experimental rockets used by kids today would not be modified and along with a finger used to target objects in the air. There comes a point where Uncle has to grant some innocence where innocence exists because, as the old saying goes, or a variant of it, "locks", or laws in this case, do not exist to keep out thieves, they're to keep innocent people innocent.

I'm sure anyone so minded could modify any of this tech to suit whatever purpose came to mind. I'd like to think that common sense is still in play here, especially with Uncle Sam. Better to state the requirements to make and use such things rather than scream "doom", and hide in corners for fear of retaliation.

No one is screaming. I am merely stating the facts to inform the less informed among us of the laws and available documents, or in this case, the lack thereof pertaining to outdoor laser displays. Until several days ago, they had been available at It was a more up to date version of

According to these laws, all outdoor lasers exceeding 5µW/cm² are banned within 10 miles of an airport. It does not specify what kind or type of airport, it just says airport. This effectively means absolutely no laser may be used outdoors, including your 5,000x more powerful cat toy. (Very generous figure, here, actually) Most people in this country live less than 10 miles from some kind of airport.
But apparently these laws are now out of date.

Thanks for the information; I hear you; and it's not clear I was thinking more broadly when I referred to screaming, it was a expression derived vicariously from the plethora of 'doom porn' littering the internet.

I think it's correct to say it's out of date; like using cellphones on planes, a knee jerk reaction from the understanding that it's practically impossible, without scrutiny, to tell a harmless transmitter (or laser, in this case) from one capable of potential harm. I think there is valid cause for concern; I understand the need for reasonable precaution.

My old home town still has on it's books a law which requires non-horse drawn transportation to stop at intersections and walk around the vehicle with a lantern so as to warn other drivers so their horses don't get spooked. It's used to stop suspicious vehicles to this day, though not abused... much.

And, you're right, I live in what's considered around here, the country; and, I have an small airport less than 8 miles from my house. I also live along a direct path flight between two military airport forts though they are 100 miles away in one direction and 50 miles away in the other, as the crow flies. And, while observing stealthy transportation I've had my cellphone disabled by ECM when trying to call my daughter who had earlier reported seeing "UFO's". Dang them things is quiet! ;-) Typical flying triangle, though difficult to tell at night, barely detectable. The cellphone wouldn't work again until I called the phone company and said, my phone quit working when something flew over. Without explanation, a few seconds later after I hung up (another phone, of course), it was working again.

So, I agree, laws are out of date; but, don't expect change, if any, to come quickly. Sad really.

Thanks for the references.


4 years ago on Introduction

Please (everyone) talk about what the created thing is made to do early in the description. Laser pointer, OK.. then all these motors and controllers.. had no good idea what was going to be the end product.

2 replies

Reply 4 years ago on Introduction

Fair enough criticism. One does tend to forget to introduce topics when you've been working on them for ages.


Reply 4 years ago on Introduction

Large telescopes use similar devices like a virtual star to gain information on atmospheric turbulence to make corrections on camera data taken with large sophisticated telescopes. Most amateur astronomers I know have tracking devices like this already built into telescopes. I think a modification of this device that could be used for smaller telescopes would certainly be in order, and wouldn't necessarily need this type of laser to function. While this doesn't fall into my scope right now; it's certainly worthwhile for consideration, and I hope someone can do this, as at some time in the future, I'd like to have one, and belong to an amateur astronomer club that would most definately be interested as many make their own large aperture/mirror scope and a positioning and tracking device would be a wonderful addition to more powerful diy scopes. This is a wonderful thing, and I hope people haven't been scared away to try other uses. Thank you for such a great instructable!


4 years ago on Step 5

How hard would it be to beef this up a little and replace the pointer with a telescope?

Would it track a star?

Would that be proctical?

1 reply

I'm fairly certain you could write a script to "repeatedly click the slew button".

In terms of replacing an actual telescope, it's absolutely possible. Of course you'd just have to find motors with the right amount of torque


4 years ago on Introduction

A nice toy. Using optical encoders from an old computer mouse may reduce the pointing error down to 3 degrees in each axis (sun/moon apparent diameter is about half a degree). Also, the device should be much more useable if the stellarium part could be eliminated. Micro SD shield with a card could easily store a small database of the brightest celestial objects and relatively simple algorithms may calculate the exact positions of stars (planets are much harder).Good job, anyway!


This looks like an awesome project! I want to take my old Meade Telescope and re-do the controls for it. This might be what I was looking for!