Space is big. Really big. Yet on TV and movies, enemy spacecraft routinely wind up meeting at roughly the same spot and, miraculously, in the same orientation. If you’ve ever tried to find something smaller than the moon in a telescope, you’ll appreciate that it isn’t that easy. There are plenty of tricks for locating objects ranging from expensive computerized scopes with motors to mounting a phone with Google Sky or a similar program to your telescope. [DentDentArthurDent] didn’t use a phone. He used an Arduino with an outboard GPS module.

You still have to move the scope yourself, but the GPS means you know your location and the time to a high degree of accuracy. Before you start an observing session, you simply point the telescope at Polaris to calibrate the algorithm, a process which in the northern hemisphere is pretty easy.

The telescope in question is a Dobson, so is easy to move and easy to sense its position using potentiometers and an A/D. The project also includes a detailed description of the math used to convert the time, latitude, longitude, right ascension, and declination into position data. One of four LEDs show if you should move up, down, left, or right. When you are on target, all four LEDs light. We assume you should use red LEDs and a red LCD filter so you don’t ruin your night vision.

There are a few sources of error and [Arthur] does a great job of analyzing and correcting each one. The project even has a nice 3D printed case. The database only contains 45 objects but it is easy to add more. We wondered if it wouldn’t have been better to use a larger computer such as a Raspberry Pi to get the stellar data — maybe even from the Internet — and rely on the Arduino to just manage the position sensing and direction indication, but then again, this works and it is very inexpensive.

This isn’t the first Arduino telescope finder we’ve seen. The last one even had a touchscreen.

[gocivici] threatened us with a tutorial on positional astronomy when we started reading his tutorial on a Arduino Powered Star Pointer and he delivered. We’d pick him to help us take the One Ring to Mordor; we’d never get lost and his threat-delivery-rate makes him less likely to pull a Boromir.

As we mentioned he starts off with a really succinct and well written tutorial on celestial coordinates that antiquity would have killed to have. If we were writing a bit of code to do our own positional astronomy system, this is the tab we’d have open. Incidentally, that’s exactly what he encourages those who have followed the tutorial to do.

The star pointer itself is a high powered green laser pointer (battery powered), 3D printed parts, and an amalgam of fourteen dollars of Chinese tech cruft. The project uses two Arduino clones to process serial commands and manage two 28byj-48 stepper motors. The 2nd Arduino clone was purely to supplement the digital pins of the first; we paused a bit at that, but then we realized that import arduinos have gotten so cheap they probably are more affordable than an I2C breakout board or stepper driver these days. The body was designed with a mixture of Tinkercad and something we’d not heard of, OpenJsCAD.

Once it’s all assembled and tested the only thing left to do is go outside with your contraption. After making sure that you’ve followed all the local regulations for not pointing lasers at airplanes, point the laser at the north star. After that you can plug in any star coordinate and the laser will swing towards it and track its location in the sky. Pretty cool.

To photograph the stars, you need a gadget that can track the revolving night sky in a perfectly timed arc. Otherwise all you’ll see is streaks and blurs.

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