For the first time since 1948, the full moon coincides with the summer solstice! Consequently, we're all enjoying the morbid doomsday prophecies that such cosmic coincidences tend to generate. A few pessimistic sages now perched on summit tops have predicted that our four billion year old Earth will crumble into flaming embers now that the moon will be full on the first day of summer. Since the world sustained no severe injury in 1948 or during any of the tens of millions of solstices during which a full moon occurred, we remain slightly skeptical at the claim that
today is our last.*
Summer begins tonight at 6:34 p.m. At this precise moment, the North Pole will be oriented as close to the Sun as possible. This orientation continously changes because our planet revolves around the Sun at more than 66,000 miles per hour. Earth is titled relative to the vertical by 23.4 degrees. As Earth travels along its orbit, the orientation of the poles relative to the Sun will always change. Today, our hemisphere points toward the Sun as far as possible. Six months from now, the southern hemisphere will be so aligned and the northern hemisphere will point away from the Sun. At this moment, winter will begin in the north and summer commences in the south.
We don't notice this planet's tilt, but we instead observe the Sun's changing altitude. Today, when the Sun crosses the meridian (reaches upper culmination) around noon time, it will be about 70.5 degrees above the southern horizon. That is the highest altitude the Sun can ever attain in our sky. In contrast, on the first day of winter (December solstice), when the Sun crosses the meridian, it will only be 23.5 degrees above due south.
Our weather is hotter in the summer because the Sun looms higher in the sky and its benevolent light experiences less atmospheric absorption. In the winter, the Sun's radiation traverses the lower part of the sky and therefore must pass through more gases before it reaches the ground. We know that the Sum heats the ground, which then warms the nearby air. If the ground isn't warmed much by the Sun. it cannot impart much heat into the gases above it.
While it is true that the Sun will start losing altitude once it reaches its apex, our parent star will remain high and beautiful for quite awhile, so we will continue to experience (in theory) hot days, warmer nights and swarms of voracious insects desperately seeking nourishment. However, the return of these pests does herald the return of summer and the myriad delights it offers to humanity.
We focus on summer this week.
Tomorrow, we answer a slew of questions pertaining to astronomical summer.
The next day, we conduct a tour of the summer sky.
*If any of these dire prognostications do come to fruition and we, let's say, suddenly find ourselves bewildered, helpless and singed on a molten Earth because Jupiter went into superior conjunction on Super Bowl Sunday, we will be the first to proffer our sincerest apologies to the dozen or so remaining survivors.