Eagle-eyed followers may have noticed that we’ve made a change to our alerts. From now on, any alerts issued during “daytime” will look slightly different:
New daytime version:
We’ve tweaked the text to avoid any confusion about being able to see the aurora during daylight hours. As you’ll probably know, seeing aurora requires dark, clear skies. We did originally have text to this affect but we agree that it did look a little confusing when we said “aurora may be visible” even during the day. Just in case you’re wondering why we even bother with daytime alerts, please read here.
Our alerts are all automated and so we have to determine when daytime occurs programatically (i.e. we don’t just look outside to see if it’s dark!). To do this, we use a routine to calculate at what time civil twilight occurs at Lancaster (UK). Civil twilight is a period of the day where the Sun appears below the horizon but is less than 6 degrees below it. So for our alerts, if the Sun is up or is less than 6 degrees below the horizon then we call that “daytime”. If it is more than 6 degrees below the horizon, we call that “nightime”.
Civil twilight, just like sunrise and sunset, occurs at different times throughout the year and will depend upon exactly where you are located. Since we don’t issue personalised alerts based specifically on your individual location, we’ve chosen Lancaster as our base. Not only is this where we’re located, more importantly, it is roughly the “middle” of the United Kingdom.
We hope that makes sense and helps with your aurora hunting planning! If you have any suggestions for our daytime alert text, i.e. if something could be clearer, then do let us know.