The VMware vSphere PowerCLI is a PowerShell extension specifically for vSphere. Installation is straightforward and you can be up and running in moments. From there, you can leverage some of its great community resources to retrieve data from your vSphere environment.
One resource is a very handy post by Luc Dekens that explains how to determine the IP, hostname, username, and session login for all active vSphere connections. This is different from the vSphere sessions screen, as it tells us only the username, the timing, and whether they are active.
In the screen shot above, the script highlighted in Luc's post is being run, immediately giving my useable information.