Does a Fully Qualified Domain Name need a period?

I'm confused about FQDN (Fully Qualified Domain Name). Is it necessary to end FQDN with a period? Like sun or sun.tuc.noao.edu. or sun.tuc.noao.edu. What's the difference?

Solution

How IT Works: Domain Name System

All DNS records actually end with the period character (.) which represents the root of the DNS hierarchy, but it's rarely printed and is usually just assumed. A domain name that includes the trailing period character is said to be a Fully Qualified Domain Name (FQDN). However, domain names where the period character is implicit are also commonly referred to as FQDNs.

^{Source: TechNet Magazine}