SKY REPORTER: High Summer

Belvedere Castle, Central Park
Credit: Stig Nygaard

At 11 am Friday July 5 Earth reached the aphelion point of its orbit, when our planet was 94,508,958 miles from the Sun. It’s the greatest separation of the year, and as we deal with summer temperatures the situation seems counter intuitive. Some years ago a large majority of students questioned on commencement day at a well-known research university cited distance from the Sun as the cause of our seasons. Of course we know tilt of Earth’s rotation axis relative to the Sun, rather than variations in solar distance, is responsible for our seasonal variations.

But why is average temperature by Belvedere Castle in Central Park on June 21^st, when the northern hemisphere is most directed toward the Sun, only 73°F. While one month later—July 21^st, a day with 27 minutes less daylight and the Sun lower in the sky, average temperatures have climbed to 77°? Also consider that on May 21^st park temperatures average just 64° while the duration of daylight and solar altitude are the same as on July 21^st when the average temperature is 13° warmer.

Such apparent discrepancies result from air, land, and water temperatures lagging significantly behind variations in the Sun’s apparent intensity due to sluggishness in absorbing and releasing heat. For example at Long Island’s Jones Beach ocean temperatures don’t reach their peak until around August 9^th and their annual minimum occurs around March 1^st. 

Societies around the world feature “midsummer” celebrations highlighting the summer solstice when, in the northern hemisphere, the sun is at the height of its ecliptic crest. However for most of us the middle of summer, often called “high” summer, doesn’t happen until after mid-July when air temperatures are usually hottest and plunging into ocean water doesn’t take our breath away. 

The Moon

Planets

Venus and Saturn are the only planets easily visible during evenings of July. They appear as twilight fades, with Venus low in the southwest and descending beneath the horizon about 90 minutes after sunset. Saturn doesn’t set until after midnight for most of this month. Jupiter is becoming more apparent and rises about an hour before morning twilight begins on July 15^th. Mars, rather inconspicuous compared with Jupiter, may be noticed close to that much larger planet during the early morning of Monday July 22.