impeccable | imˈpekəb(ə)l | adjective (of behavior, performance, or appearance) in accordance with the highest standards of propriety; faultless
ORIGIN mid 16th century (in the theological sense): from Latin impeccabilis, from in- ‘not’ + peccare ‘to sin’.
There is seemingly no distinct (or meaningful) juncture of transition from springtime to summer apart from the Summer Solstice that historically marks the onset of summer at the time of the longest day, about June 21 in the northern hemisphere and December 22 in the southern hemisphere.
The Summer Solstice this year is Wednesday, June 21 at 10:57 am. The summer solstice, also called the festival solstice or midsummer, occurs when one of Earth’s poles has its maximum tilt toward the Sun. It happens twice yearly, once in each hemisphere.