Oh, Ranger! Story Tour Video Gallery
The Ansel Adams Gallery provides the only classes that are given year round (and that has pre-registration) in Yosemite, and you can sign up for classes on their website, www.anseladams.com.
The American Park Network, in conjunction with Canon, host Photography walks in several of the most visited parks in the country. We do not have any of the current dates or locations for next Summer's sessions. If you were looking to sign up for one of those classes, we do not in fact require pre-registration. Our free photo walks are given 2-3 times daily, and are on a first come, first serve basis. If you would like to know more about the dates and locations of those classes, you should return to our site in the Spring as we lock in our dates and locations for the 2011 tour.
Lastly, I am not sure if there is a night sky program in relation to a photo program. There are special Night Sky programs offered through the National Park Service, and can be found in the NPS Yosemite Guide.
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Rangers usually work 40 hours a week with frequent overtime and
weekend work in the summer when the use of the parks increases. 
Nature Trails The bosque, or riverside forest, features two miles of nature trails that wind through tall cottonwoods and past willow thickets and open sand flats alongside the Rio Grande. Birdwatching During the fall and winter months, sandhill cranes, Canada geese, and several types of ducks take advantage of this peaceful pitstop. ...
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