Show HN: AstroHelm – Use your phone camera to aim a telescope or telephoto lens
astrohelm.appHello HN!
As an amateur astronomer living in New York City, finding objects in the night sky has always been a huge challenge. I thought about using the smartphone's gyroscope and magnetometer, but the accuracy left a lot to be desired.
Then I learned about plate solving: given a picture of the sky, we can determine exactly where in the sky the camera was pointing by identifying the star pattern. This was a much better fit - as long as the phone and the optics are rigidly connected, we can repeatedly photograph the sky and determine the pointing direction with very high accuracy.
A lot of work was done to design an algorithm that works reliably with smartphone cameras, which have limited light sensitivity and wider field of view which includes buildings and trees. I experimented a lot with machine learning, and to my surprise, traditional CV methods actually performed better at extracting stars from the image.
The result is AstroHelm, an iOS and Android app that helps figure out where your telescope or camera is pointing, and guides you to the object of your choice. Just follow an arrow on screen, and the object will land right in your eyepiece or viewfinder. Everything happens on device, and no internet connection is required.
AstroHelm is free to use and comes with beginner-friendly objects selected for each night. Optional one time purchases unlock more objects and advanced features, such as interoperability with other astronomy software. I am also proud to partner with astronomy clubs and organizations to offer free licenses for outreach.
I hope AstroHelm can make it a little easier to discover the wonders of the night sky, and I look forward to your feedback!
Hey, I'd actually use that. I build telescopes (see personal site in profile) and only do visual astronomy. I voluntarily prefer to use old-ish phones, i.e. currently I am using an iPhone SE 2022. Do you think the weak signal under the night sky would work with your plate solving ?
It should. I have users reporting good experience with iPhone XS. It is heavily dependent on your local light pollution levels though.
- Accurate up to within 10 arcseconds (1/360 of a degree)
- Computes coordinates in less than a second</i>
For comparison, the sky moves 15 arcseconds per second. So without a motorized mount to keep the telescope on target, the accuracy will be short-lived.
OP mixed up accuracy and resolution.
Since the plate solving happens periodically, the sky drift will quickly be corrected!
Did I get this wrong, is this not meant for manual pointing? In which case corrected does not seem the right description, it will observe the sky rotation and add 15" to the pointing error every second, I have to manually correct that when things move out of the field of view.
Yes, the pointing shown in the app will always be correct, just the object will move out of the field of view. You need to manually track the object using an equatorial mount, or use a clock drive or similar.
It's meaningless anyway, unless you have a calibration approach the home page doesn't mention. Aligning a phone to within 10 arcseconds of where your scope is pointing is... ambitious :)
It would be easier if you could use an eyepiece adapter. I have no idea why the page claims "The field of view is typically too small for plate solving to work." for that approach - it works just fine with a FOV of at least 0.2 degrees or so, which is much smaller than what most beginner/intermediate scopes have.
And if you do have a scope with a smaller TFOV, I'd argue you're likely not the target audience for the app. (Yes, you can get there cheaply and as a first scope, but it's not the usual route)
Edit: I want to be clear it's not a diss on the app - it's great. Plate solving at that speed is pretty cool. I just wish it'd work at smaller TFOVs :)
So the reason that line of text is there is we designed AstroHelm to be mounted directly on the telescope facing the sky. We don't want our users to go to Amazon and search for "telescope smartphone mount", get an eyepiece adapter, and found that it doesn't work :)
As for why we don't support adding optics between the phone and the sky, there are a few reasons. The accuracy from phone's camera lens is good enough, and we don't want to introduce complexity. The plate solving algorithm also benefits heavily from knowing the field of view, which you get from phone's built in camera but need user input for custom optics. Finally, supporting smaller field of view means shipping a much larger star database which most users won't use, so it's just a waste of storage and bandwidth. Not to mention blind solving a small FoV would be very slow and not work interactively.
For alignment, we support two alignment methods. You can align it like a finderscope, i.e. aim your telescope at a distant treetop and drag the crosshair over it. Once you begin observing, you can also sync to the object, which should give you better accuracy.
This looks like a nice alternative to PiFinder. No extra hardware required. https://www.pifinder.io/
Looks cool! Plate solving is an incredibly useful technology for astronomy, putting it into the smartphone makes it available for a lot of "non-smart" setups. Only one question: does it have a polar align feature? This is my biggest challenge, when e.g. setting up a simple star tracker. The app would be very useful for this.
We have a prototype polar alignment feature in the works! The benefit of plate solving is you can actually do a two-point polar alignment: just take two pictures with different RA, and we will know where the axis is. Taking more pictures would improve accuracy.
Interesting, thanks.
A related issue I’ve been wondering about: Why don’t gimbals for cameras and smartphones offer an astrophotography mode for long exposures of the night sky?
They do! The "night mode" in camera apps all utilize gimbals
Really dumb question - but how does the phone know the distance from your phone lens to your telescope lens? I assume this varies greatly from mount to mount and will change how accurate the app is?
The distance doesn't matter, since the stars are almost infinitely far away, so there's no parallax. You do need to correct for the angle though. We support daytime alignment using, say, a distant treetop, or at night align on the object you are observing.
Ah, that's the piece I was missing. Thank you
just getting into astrophotography - seeing a few apps for that purpose have been fun.
@HeavenFox - also in NYC - drop me a line over at allisterk.com if you have a chance!
Good call ditching ML. Traditional CV still wins on power, latency, and determinism for star centroiding.
This looks great, but why is there no "plus" version for Android?
We launched Android recently and was using this opportunity to experiment with pricing and packaging a little bit!
I often use Stardroid/SkyMap for this, which is free (open source) software
https://github.com/sky-map-team/stardroid
I’m not a professional by any means and am pretty new to astrophotography. Looking at the Stardroid repo there, it looks like it’s using GPS+Compass+IMU for pointing. That’s awesome for coarse positioning, but Plate Solving (what AstroHelm is doing) is using the photos themselves to do fine positioning. https://nova.astrometry.net/ is an open service that can take images and tell you where in the sky you were pointing. https://nighttime-imaging.eu/docs/master/site/advanced/plate... has some more details about different techniques and software packages. My understanding is that is basically identifies the 4-8 most prominent stars in the image and the angles between them and does a nearest neighbour search in a massive database. Pretty cool!
Ah interesting, I thoughy this was also using IMU
>"Works Offline
The best dark-sky sites don't have Internet access. AstroHelm’s plate solving engine runs entirely on device. No internet connection required, and your camera images stay on your phone."
This looks like a great tool for the following application:
o Off-grid, deep wilderness, high mountain, broad desert or ocean navigation (like the way ancient seafarers would navigate via the position of the stars in the nighttime sky, relative to them)
(Also, if you're a Star Trek fan and/or futurist, you'd expect that computers on future spacecraft would or could run some version of this software, or at least some form of Plate Solving / Astrometric Solving algorithm...)
Anyway, the app looks great!
Related:
General wikipedia information page about Astrometric Solving (does not include algorithms!):
https://en.wikipedia.org/wiki/Astrometric_solving
Paper: New Algorithms for Automated Astrometry, by Chris Harvey (2004) (An excellent paper about all that is necessary for such an algorithm!):
https://cs.nyu.edu/home/people/in_memoriam/roweis/papers/Har...
> The best dark-sky sites don't have Internet access.
I'm spoiled. The best dark-sky site near me, a meager 4 hour drive, is an astronomy campus with fiber internet providing wifi. Intentionally, it's not a lot of bandwidth to do streaming while you're bored, but enough to run apps like this. They also have a what they named the StarField which is an open field where there is a grid where every 10' or so has an electrical outlet popping up from the ground to power your gear. It's the darkest skies in my state that is not federal land.
Cool project!
Pls fix (AI slop?):
But:
“After that, whatever I called for was in the field of view, even when I was using a 5mm eyepiece.”
They mean that the FOV seen by the phone through an eyepiece is too small to run a successful plate solve.
The comment of the user says "the plate solve was precise enough that the object I wanted was centered (for the observer, not for the phone) when I used a 5mm eyepiece" (which is usually an high-power, meaning tiny-FOV eyepiece)
Most pointing methods aren't accurate enough to correctly center an object at high power and require you to use a lower power eyepiece, nudge the object a bit, then switch to high power. I understand how you read it as slop but the two sentences aren't contradictory, and the user comment hints to an useful pointing tool :)
Edit : bad tenses and grammar fixes
Thank you for the explanation!
For more context, the other comment saying "I’m really impressed… guided me almost dead on to the double cluster when asked." is a bit funny, because the double cluster is easily seen naked-eye in suburban sky, which is as easy as it gets for deep sky objects. But the comment you quoted makes the app look good and I'm going to try it if the fall cloud cover ever goes away.