Guides
Guides
What the numbers mean, in the words of the agencies that publish them, and what this app does to them.
- AuroraHow to read the Kp index, the solar wind and NOAA's G1 to G5 storm scale to judge whether an aurora is likely, with NOAA's own wording of how far from the poles each level has been seen.
- Tropical stormsWhat the Saffir-Simpson categories measure and leave out, what the National Hurricane Center's cone does and does not show, and how forecast hours are counted.
- EarthquakesWhere earthquake data comes from, how often it updates, what PAGER alert levels mean, and why nobody can tell you when the next one will be.
- FiresHow NASA's satellite fire detections are collected, how fresh they are, what we leave out and why a cluster of dots is not a measure of a fire's size.
- AsteroidsHow to read NASA JPL's list of asteroids passing near Earth: distances in lunar distances, how sizes are estimated and why a close approach is not a threat.
- SatellitesWhy satellites are only visible near dawn and dusk, how their positions are calculated from orbital elements, and how fresh those elements need to be.