def is_midday(this_t):
    """
    Return true if this_t is "mid-day" in North America.  "Mid-day" is
    defined as between 15:00 and 23:00 UTC, which is 10:00 EST to
    15:00 PST.

    INPUTS
    this_t: a datetime.datetime object

    OUTPUTS
    True or False
    """
    return ((this_t.hour >= 15) and (this_t.hour <= 23))