OverTwitter
Between 2009 and 2014, I ran a series of Twitter feeds that alerted followers to visible passes of the ISS, Hubble, and other satellites over cities around the world.
Inspired by the @abovelondon Twitter feed that reported upcoming visible transits of interesting objects over London, I created several similar Twitter feeds. It began with @overcardiff, a feed covering my own home city, and I then took requests for other places all over the planet. These feeds are no longer active.
What did these Twitter feeds tell you? The feeds determined when the International Space Station (ISS), Hubble, Envisat and other interesting objects would be visible in the relevant location. They also alerted followers to bright Iridium flares: elusive, momentary flashes of reflected light from the Iridium constellation of satellites, which could often be seen in daylight. When the time approached, an alert appeared on the Twitter feed, giving 30-45 minutes warning of a sighting opportunity.
Which cities were covered? There were Twitter feeds for cities around the world. If you lived within 20 miles of one of the covered cities, the data was still correct for your location. Within 50 miles, the data was only about a minute out in most cases. Tweet alerts only appeared when the weather in the location was good enough to see the transit. The weather data came from Yahoo! Weather. Each tweet gave the same information, for example:
The ISS will pass over Sydney at mag -1.7 at 4:32am on January 25th. Moves from 46deg elevation SW to 10deg elevation SE over 3 min.
The mag number referred to the brightness of the object on the magnitude scale, where lower was better. After that came a pair of coordinates on the sky showing the beginning and end of the track. ‘46deg elevation’ meant 46 degrees above the horizon (where 90 degrees is directly overhead). SW and SE were compass directions around the horizon. The duration of visibility was given as ‘3 min’.
RSS Feeds I also offered RSS 2.0 feeds for visible transits in any location. Users could use a map to find their location and generate a custom RSS feed, or point their RSS reader directly to a URL with their latitude and longitude. This service is no longer available.