netstat output question

netstat -a -> outputs:

edit: added the column headers:

Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address           Foreign Address         State
udp        0      0 <domain redacted="">.:47949 50.28.8.224:ntp         ESTABLISHED
udp        0      0 <domain redacted="">.:52313 mail.freerip.com:ntp    ESTABLISHED
udp        0      0 <domain redacted="">.:52074 conquest.kjsl.com:ntp   ESTABLISHED
udp        0      0 <domain redacted="">.:52148 barricade.rack911.c:ntp ESTABLISHED</domain></domain></domain></domain>

What are these, and should I be concerned?