How do I interpret the output of my last command?

How do I interpret the output of my last command?

This is what my last command shows:

user123 pts/0 :0.0 Tue May 28 08:10 still logged in
reboot system boot 3.2.0-43-generic Tue May 28 08:07 - 08:46 (00:38)
user123 pts/0 :0.0 Sun May 26 20:46 - down (00:00)
reboot system boot 3.2.0-43-generic Sun May 26 20:45 - 20:46 (00:00)
user123 pts/0 :0.0 Thu May 23 12:35 - 12:35 (00:00)
reboot system boot 3.2.0-43-generic Thu May 23 12:33 - 12:35 (00:02)
reboot system boot 3.2.0-43-generic Thu May 23 00:03 - 00:10 (00:07)
user123 tty4 Thu May 23 00:01 - down (00:01)
user123 tty4 Thu May 23 00:01 - 00:01 (00:00)
user123 tty4 Thu May 23 00:00 - 00:00 (00:00)
user123 tty4 Thu May 23 00:00 - 00:00 (00:00)
user123 pts/3 :0.0 Wed May 22 22:54 - 22:57 (00:03)
user123 pts/2 :0.0 Wed May 22 22:44 - down (01:18)
reboot system boot 3.2.0-43-generic Wed May 22 22:43 - 00:02 (01:19)
user123 pts/2 :0.0 Wed May 22 20:59 - 21:00 (00:00)
user123 pts/2 :0.0 Wed May 22 20:56 - 20:57 (00:00)
user123 pts/2 :0.0 Wed May 22 20:53 - 20:55 (00:01)
user123 pts/2 :0.0 Wed May 22 20:52 - 20:53 (00:00)
user123 pts/2 :0.0 Wed May 22 20:51 - 20:52 (00:00)
user123 pts/2 :0.0 Wed May 22 20:50 - 20:51 (00:00)
user123 pts/2 :0.0 Wed May 22 20:47 - 20:50 (00:03)
user123 pts/2 :0.0 Wed May 22 20:40 - 20:46 (00:06)
user123 pts/2 :0.0 Wed May 22 20:38 - 20:38 (00:00)




How shud I interpret this? Shouldnt reboot entry be a specific time and not a time range? And why are my login sessions divided into so many small intervals?