Blue hour for iOS
The app only using location services to determine your location and the same formula that I'm using on this site to get exactly the same results you got used to on the website.
I have many other and new ideas for the app but I wanted to roll the first version out as soon as it has the same functionality as the website.
The app is available on iTunes Store for $1.99
If you have any ideas, questions, suggestions or bug reports about the app, please use the contact form.