Experience provided the fixed settings: white balance shade, ISO 1600, F-stop F3.5. Varying shutter speed capture starlight in different ways. Here's a full series posted on Flickr.com Night sky at Wildcat Mountain State Park in October. I did a wide assortment of shutter speed settings. Fraction of a second upwards to 290.0 seconds.
I imagined a fractoin of a second would be completely underexposed. Nothing but a black sky. But even a few seconds shows very fiew stars. Notice less than 15 seconds the stars are barely visible against the darkness.
Stars begin to appear around 16 seconds (not shown) and really begin to sparkle 28 seconds.
Somewhere around 42 seconds the photo looks like the familiar night sky.
Around 70 seconds the stars blur but not in a desireable way. However very long exposures more than 120 seconds and the stars begin to rotate in the sky. Creating long streaks of light as shown below with 290.0 seconds exposure.
There are multiple ways to approach really long exposures. Really long exposures cut down on the ISO and up the exposure time.
Long exposures its important to remember about doubles and halves. If you cut the sensitivity from ISO 1600 to ISO 800 you need to double exposure time. Manipulate how the sky looks using long exposures. Varying the settings can have unexpected results.
Why do the stars blur? Why does the night sky seem to have a curved look on the star's motion? Controlling motion blur is a lenghty subject for another lesson.