rockym93 dot net

archive · tags · feed

Stationary

09 July 201510:40AMthings

I have a bit of a confession to make. I can't actually code very well. Most of what I do is use my rudimentary Python skills to clumsily glue things together and the release them into the wild and hope they don't break.

It's a decent way to kill a day off though.

The latest one of these is ISSBot.

The coolest thing about the International Space Station is- wait, no. It's not that. It's that it's an incredible orbiting science lab in space whizzing over our heads all the time filled with actual living humans who get there on rocket ships.

The second coolest thing about it is that you can actually spot it doing that orbiting. NASA publish good sightings on their website, and you can watch it pass overhead. They also publish a set of orbital parameters, so that you can calculate that kind of thing for yourself.

ISSBot, using someone else's API to that data, can let you know, using someone else's API to the messaging software Telegram, about not just visible passes, but every time the ISS passes over you* - and how long that pass will be. It will also, with a little coaxing, tell you where the station is right now.

You can find the source code at http://www.rockym93.net/code/, and talk to ISSBot or add it to your chat at http://telegram.me/ISSBot

a screenshot.


* So, a little bit about what makes a pass visible, why filtering those out is tricky to implement, and why NASA's data - while trickier to scrape - is probably better.

The station orbits the earth about 16 times a day, and is inclined at an angle of 51.6 degrees. This is so it can be accessed and contacted from Russia, which is quite a long way north - but still be accessed by the Space Shuttle too.

not to scale.

This is what gives you that distinctive spacey-looking orbit path when traced on a map.

still not to scale.

Now, if the station was in Geosynchronous orbit, a lot further up, and orbited the earth exactly once every 24 hours instead of every 90 minutes, that wiggly path would always pass over the same spot. But it doesn't. The ISS is in a pretty low orbit - so low that they have to worry about drag from a wispy bit of atmosphere. That means it's moving much faster, and so the earth's rotation and the station's orbit are out of sync. That path shifts across a different part of the earth's surface every single orbit.

So what does all of this mean for spotting the space station?

  1. If you're north or south of about 51.6 degrees latitude, the station will never pass directly overhead. I haven't done the research, but I doubt it'd be visible at all much further north of that. If you're not, because the station is orbiting so many times a day, the station is probably passing overhead a lot more frequently than you might think. But not all of these will be visible, because
  2. The station shines not because it's producing light, but because it's reflecting it. That means that to spot the station, it has to be in daylight, but - for optimal viewing, you have to be in darkness. And since it's not all that much further above the earth than we are (and thus not bathed in perpetual sunlight, unblocked by the earth at all) the best times to spot it will be around sunrise and sunset, when you're in the dark, but the station can still catch the sunlight.
  3. The station will be visible in a roughly circular area centred immediately below where it's passing directly over, but lower on the horizon. Beyond that area, it will drop below the horizon. So a pass doesn't have to be directly overhead to be visible. The closer to the center of that circle you are, the longer you'll be able to see the ISS.

So with that in mind, here is how you use the pretty scant data ISSBot can give you (time, duration, and current location) to actually spot the ISS. 1. Wait for a pass that is around sunset. I don't have any hard numbers on this, but I'd say within an hour is probably your best bet. 2. Wait for a pass that is longer, rather than shorter. Not only will this give you more time to do your spotting, but it will mean the station is higher in the sky and thus easier to see. 3. Watch the station as it approaches. As it gets close to you - and this is going to sound a bit obvious - look towards it. If it looks like it will pass to the south of you, look south. If it looks like it will pass to the north, look north.

Alternatively, just use it as a novelty, and marvel at how gosh darned nuts it is that there are astronauts flying over your head at 27 and a half thousand kilometres per hour, balanced right on the edge of space.

< Don't break the chain New World Order >