AOS/LOS information about look4sat

[rt-bishop]

Hey Eugenio! Thanks for your message and I'm really really glad you're finding my side-project useful =) I created it as my way to say thank you to the broader radio amateurs community. There is so much free knowledge and helpful people out there. Also this means that there is no central place where all the knowledge is stored and shared, but lots of various websites, books, discord and telegram chats where it's possible to gather the pieces and put it all together.

Regarding the particular question: AOS stands for Acquisition of Signal (or Sight) - the time when a satellite rises above the horizon, and LOS is Loss of Signal (or Sight) - the time when a satellite goes below the horizon. In most places we've got buildings, trees etc, so even if the satellite raised above ground it may not mean that a person could immediately start getting the data from the satellite via radio, or be able to see it.

Regarding the time it takes the satellites to pass overhead: There are several types of orbits and satellites usually fall into the corresponding groups. Here's a really nice picture https://en.wikipedia.org/wiki/Low_Earth_orbit#/media/File:Orbitalaltitudes.svg. The only thing that really matters in space around Earth is the orbit. It's very tightly coupled with the speed the object is travelling around the planet. So for Geostationary satellites (Altitude ~35000km) their rotation speed around Earth will match the actual rotation of the planet, so from our perspective they are always at the same position.
For LowEarthOrbit satellites it's much more interesting. Basically the lower the orbit - the quicker the satellite passes overhead. LANDSATs are at ~700 km and ~12 minutes is the typical time those satellites can be observed for. For example ISS is on a much lower orbit ~400km and it passes overhead even quicker.

Regarding the documentation that is useful, I'd recommend several websites like https://www.rtl-sdr.com/, https://www.amsat.org/, https://satnogs.org/ and of course Wikipedia. As for the orbital motion for me the best teacher was Kerbal Space Program computer game - https://store.steampowered.com/app/220200/Kerbal_Space_Program/. It's very close to real life physics and beautifully descibes the motion in Space (and the pain of docking several space ships together).

Hope I managed to clarify several things. If not, please let me know either here or via email. And just once again, I'm super happy that so many people find this little project very useful! Cheers!