def date_range_to_str(start, end):
    """
    Converts the provided validity range (with starting and end date),
    into a human-readable string.

    :param begin: Start date in UTC.
    :type begin: datetime.datetime

    :param end: End date in UTC.
    :type end: datetime.datetime

    :returns: String representation of date range, up to a second granularity.
    :rtype: str
    """
    date_format = '%Y-%m-%d %H:%M:%S UTC'
    return '%s - %s' % (start.strftime(date_format), end.strftime(date_format))
