As you've no doubt noticed, here in North America the skies are very crisp and transparent in the winter -- when the clouds have parted, of course. We also get the brightest star in the sky, Sirius, and some lovely constellations.
I've got two really well-done astronomy apps for you that have just received significant updates. One is pro-oriented, while the other is more for casual sky watchers.
First up is Sky Guide (US $1.99), an App Store Best of 2013. Sky Guide has wonderful graphics, and almost all navigation is done with gestures, leaving a very uncluttered screen. This latest version features time-lapse controls, so you can speed the sky up by 30,000 times if you want, watching planetary conjunctions and the life and death of comets. Of course, you can hold your iOS device up to the sky, and the screen will mimic your position to make identifying that star, planet or galaxy that much easier. There is also a way to have the screen match how dark your sky is -- use two fingers and swipe up and down. In very dark locations, you will see an excellent rendering of the Milky Way.