Gaps in Stars

Hello,

I shot this star trail photo the other night. I actually left my camera out while I went to bed. This is made up of 495 photos. Each a 30 second exposure using my camera's internal intervelometer. With a 1 second interval. The lowest it will go.

My question is why did I get so many gaps in my trails in this. I did another one the previous night only using 165 photos and it came out much better. Albeit, it also had a few small gaps in the trails. What am I doing wrong here? Any advice to get smoother long trails with out gaps?

I used the lighten blend mode in photoshop to blend the trails and clean up any planes and satellites. To get rid of the planes and other distractions I just paint them out with a black brush since I'm using lighten blend mode. Could this be the reason I'm getting those gaps? Any advice would be appreciated. Thanks.