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Comment by guillaumec | Hacker News Reader

I am one of the developers. Nice to see the project getting first page of hackernews. If you have any technical question about how it was done, feel free to ask.

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Very nice work; I've enjoyed using Stellarium several times, in night mode, to find various stars and planets in the sky, and it's wonderful to see a web version now.

I'm curious about something: on your Github project, you mention using a CLA, but it sounds like the only reason you're using it is to ensure provenance and irrevocability of contributions. Given that, have you considered using something like the Developer Certificate of Origin (DCO, AKA "Signed-off-by"), which has built-in support in Git and much broader acceptance in the FOSS community?

Where can we find the C source to the stellarium-web-engine.js file? thanks!

edit: It looks like this is it https://github.com/Stellarium/stellarium-web-engine

That's the one.

I was expecting a lot more code, you guys did a great job cleaning up and reducing the original desktop codebase.

Yes, but here having a small code is a necessity since we can't have a too big final executable on a website. I am actually still thinking we could make it even smaller.

Stellarium was a fine achievement a decade ago ... and has become more beautiful and useful ever since. It is certainly among the top-100 the 'rock stars' of software, and unsurpassed as a science-learning tool. Many thanks to you all!

What's the data store? And apologies if this is a dumb question, but given the number of astronomical objects in the universe that we might identify, is there some special consideration given to how large the amount of data stored might grow to?

Server side we have a mongodb database that contains the list of all the searchable objects. It is generated mostly using common stars and nebulae catalogs.

For streaming the data with good performances we also have an amazon S3 instance where we store compressed tiles of data. Each tile contains information about objects in a small region of the sky inside a given magnitude range, so when the user zoom in and out, we can download only the tiles of the visible portions of the sky.

That's how we can render the whole Gaia catalog, containing about 1 billion stars. You can try it: zoom in, and you will see the stars being loaded on the fly.

As for the database size consideration, it will most likely be an issue once we start to support queries into the Gaia catalog (about 500GB of data). There are some ways to make it work though.

How are you guys constructing the DB from the catalog? Do you plan to grow it?

For Gaia, it would be impossible (or too expensive) to put the whole catalog into a conventional DB. The solution is probably going to be something similar to OpenDAP (https://www.opendap.org/), but I haven't looked much into it myself.

Any plans on integrating with the Virtual Observatory, or is that too slow to integrate nicely?

One of the goal for the web version is to allow displaying sky observations yes (we are working on it). Not specifically from the VO, but it could as well.

i've used the desktop version (which i love, thanks!) -- how was it ported to the web?

The web version is a full rewrite of the original code, with less features and smaller code. It was designed to work on the web from the start. We try to keep the style similar though.

Wait, so the web version is a C rewrite that is then emscriptened to JS but was specifically intended for the web? That's really interesting. Can you say a little bit about how you decided to take that approach?

In the end the target is web assembly, so even writing the code directly in js would require some compilation. Why C and not an other language that can be compiled to web assembly? I guess that was mostly a question of taste.

Ah, the web assembly target is for performance? I'm curious about the process of getting from 'let's put Stellarium on the web' to 'we're going to do a clean, pruned rewrite in C and spit out web assembly'. Like, did you sit around and think deep thoughts about various options? Or did someone look at web assembly and think 'huh, webassembly might be a neat way to port Stellarium to the web'.

I think it was mostly because we knew we could do it this way. Having a C code base is also nicer for integrating back into Stellarium desktop, do other platform ports, etc.

Makes sense, thanks for indulging my nosiness!

I'd love to help make the stellarium.org site responsive. Nice docs for your Jekyll site set up.[0] I'll dig into the files to grok your workflow and submit a PR for something small at first to get your feedback, say maybe the post pages.

my github username === my hn username

Cheers! And thanks for your team's work!

[0] https://github.com/Stellarium/stellarium.github.io/blob/mast...

Thanks, that would be a nice contribution!

Hi @guillaumec , Thank you for this wonderful software.

Are the places, online or real-world, where I can get training on using Stellarium? I want to enjoy this software, but my usage has been cursory for many years now. Where can I find more information about both the concepts of Astronomy and using Stellarium for those? A video course or a in-person session would be beneficial for me, and I believe, for many others. Thanks again!

Was just using it to find where Sgr A* was in the sky a few minutes ago, I love how big the database is. Thank you!

Currently, there are about 2 millions searchable deep sky objects, plus all the Hipparcos star catalog (about 100,000 stars).

If you zoom in you can actually see the entirely of Gaia dr2 catalog (about 1 billion sources, mostly stars).

We also have most of the major solar system bodies.

Very nice. It does not work under Firefox in Debian unstable, though (the UI works, but there are no stars). It works with Chromium.

Same with Firefox (61.0.2) on Arch

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