I recently discovered a cool free app for the iphone called LUMOS. With it, I can point my phone to the sky and see exactly where the sun- or moon- is going to be positioned throughout the day (or night). Before I go into why this is so cool, take a look at these screen shots. I selected Lumos on my iphone and held it up to the sky to see where the sun would set that day. I can follow what the path of where the sun will be until sunset. The app shows where the horizon is with a blue line. Even when the phone camera is a little crooked, the software will still mark the horizon correctly.
I got curious- around what date would the sun set closer to the lighthouse? There is a date feature you can easily set and you can see the path of the sun any day of any year. So this shows the same scene, but with the sun's path on January 26. It sure would be useful to use this app if you are scouting a location for a future painting, wouldn't it?
Have you ever gone to a new location and have been disoriented about where the sun is moving? Lumos will help!
OK, here's another cool use for this app. Supposing you want to set up in the shade to paint. With this app you can see how long you will have before the sun peeks through. I recently set up at a Plein Air Quick Draw in full sun, knowing with confidence that in 20 minutes, I'd be in shade for 2 hours.
And if you want to do a nocturne, Lumos will help you plan ahead, You can see where and when the moon (and sun) will rise and set, (see black "moons" below- which also show if it's a crescent or full moon.). The software has additional features that you can pay for, but these mentioned are all free, and very helpful. It's super-simple to start using right away.
Below is the screen for Lumos (and note the upper left hand corner graphic is what you will look for when downloading the free software on your iphone), Two other features, Map and Shadow Length, are nifty too, but I'll let you discover those on your own! Let me know if this app helps you- I'd love to hear from you!