Clocks in Northern Ireland advance one hour at 1am this weekend. The change occurs when 1am becomes 2am.

The new period brings one hour ahead on clocks. It is known as Irish Summer Time or British Summer Time. This provides more evening daylight and less morning daylight.

The term sometimes used is Daylight Saving Time.

Clocks return one hour at 2am on Sunday October 25. That shift precedes Hallowe'en. It establishes Greenwich Mean Time.

The dates vary yearly. A mnemonic aids recall: spring forward, fall back.