I´m assuming you know how to set up an environment map, and how to use the Material Editor for this tutorial...
Step 1.
Open Material Editor and select an empty slot. Go to maps->diffuse and add a noise map - name this map "parent".
Step 2.
Apply the following settings to the noisemap and leave those i dont mention to their defaults.
Noise Parameters :
Noise Threshold High: 0.7
Now add a new noise map to the colour #1 map slot (its the black one) - and name this noisemap "child01"
Step 4.
Now go to the parent noisemap - and copy the child01 noisemap to the white map slot - and rename the copy "child02"
Step 3.
Apply thefollowing settings to the new noisemap - and leave those i dont mention to their defaults :
Coordinates : skip this part.
Noise Parameters :
Size : 1.0 (this defines the max size of the stars)
Noise Threshold Low : 0.69
Output :
RGB level : 5.0 (this makes the stars brighter)
Step 5.
In the child02 noisemap´s Noise Parameters, animate the Phase from 0 in frame 0 to 3 in frame 100.
By only animating the phase of one noisemap, you have ensured that there will always be some static stars, instead of having them all flicker.
Now apply the parent noisemap as environment map, specify output path and filename/type and hit render.
I know its not perfect, but it can be fitted to your specific needs with a little tweeking.
