I think the mean to say every 20 seconds exposure, if the shutter was open that long there would be streaky crap everywhere wouldnt there?
We contacted the owner of Skunkbayweather.com and they were very forthcoming with information and were happy to answer detailed questions regarding the photo as part of our investigation. They sent us the link to the entire timelapse which you can watch here, and went over the specific angle and field of view that the camera catches, as well as the camera type and its settings:
“It is a Canon T3 Rebel set up as a webcam. Images are captured about every 40-45 seconds. 3.5/20 second exposure/ 1600iso. I only run it on clear nights or when there could be severe weather.”
Check out long exposure photography. Only streaks if it moves.
Only for visible moving objects during that time period.