Aurora: Northern Lights Odds

urora answers the question every northern lights app skips: can the aurora reach your place at all, and what would it take. It works out your geomagnetic latitude, the Kp level at which the auroral oval reaches you, how dark tonight gets and when the moon is in the way. Then, beside all of that, it shows the state of the solar wind as it was last measured, with the time of every number.

The oval sits around the geomagnetic pole, not the geographic one. Edinburgh and Moscow lie on the same parallel and are 6.6 degrees apart in the latitude that decides this, which is why Scotland sees the lights a few times a year and Moscow almost never does. Aurora starts there.

YOUR PLACE, WITHOUT A NETWORK
• Your geomagnetic latitude from the International Geomagnetic Reference Field (IGRF-14), for the year you are in
• The Kp at which the oval's edge reaches you, including the honest answer when it does not reach you anywhere on the scale
• The oval rung by rung, Kp 0 to 9: how far north of you its edge would be and how high a display there would stand above your horizon, or how far past you it has swept
• Your own northern skyline, set once, so a ridge hides what it would hide

TONIGHT
• Three conditions on one time axis: dark enough, the moon out of the way, and both at once. No score: you see which part makes a night short
• Nautical or astronomical darkness, and how much moon you will put up with, are yours to set
• When there is no dark window it says why in a sentence: the sun does not set here in June, or it only reaches -8 degrees

THE STATE NOW
• The planetary K index from NOAA, named as the three-hour index it is, with how long ago it was measured
• Bz with its direction as a word, south or north, because the sign is the whole meaning
• Solar wind speed and density, minutes old
• The forecast index, kept apart from what was measured
• No network, no problem: the rest of the app works without it, and the last values are shown with their age

YOUR OWN TABLE
• Log what you saw, in your own words for how strong it was. The app stores the state of the sky with it
• After a season, the lowest Kp you have ever recorded a sighting at, for each place you watch from. A record of what happened, measured on your own horizon

ALSO
• Red night mode, red on black and nothing else, with the banner switched off
• A home-screen widget with the last measured index, its age, and the level your place needs
• An optional note when the measured index passes the level you choose. It says what changed, never what will happen
• Articles: why your latitude is not your latitude, why Kp is three hours old, why Bz points south, why the oval is seen from further than it reaches, the summer problem, and why this app does not promise

WHAT IT DOES NOT DO
It does not rate the night, invent a percentage or promise a display. The aurora has a forecast horizon of under an hour, and the app shows you the parts rather than pretending to add them up.

The only thing fetched is a global public measurement from the NOAA Space Weather Prediction Center. Your place is never part of the request, and your log stays on the phone.

Free to install, with ads. Everything in the app is free, the note and the full log included. A single one-time purchase removes the ads and nothing else.