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Driftless Dark Skies

John Heasley

Time seems to slow down around the solstice. It takes an extra half minute for the face of the sun to slip below the horizon on the June 20 summer solstice than it did on the March 19 vernal equinox. There is the slowest change in the time of the sunset. It varies only 10 minutes (between 8:35 and 8:45) this month. And there is the slowest movement from day to day in the spot on the northwestern horizon where the sun goes down. All month, this point changes less than 2 degrees. That’s about the width covered by your thumb held at arm’s length. The language enthusiast in me is delighted to remember that solstice comes from the Latin sōlstitium, sōl (“sun”) + sistō (“stand still”).

Enjoy the slower pace and be sure to savor the colors. Our atmosphere is much better at scattering blue light than red light. Yep, that’s why the sky is blue. And the sunlight needs to travel through more of this atmosphere when it’s low on the horizon, so it’s safer to look directly at the sun and to be wowed by the red and orange light that makes it to our eyes after so much of the blue is scattered. Take time at sunset (around 8:40 p.m.) and turn your back to the setting sun. There in the southeast, you will see a pinkish arch of reflected light (the Belt of Venus) and below it the darker indigo band of Earth’s shadow as it rises from the horizon. You are watching as our planet slowly rotates into night. If you are an early riser, you can experience the same things in reverse during sunrise (around 5:20).

Summer solstice is also the time of the most sunlight (over 15 hours here in the Driftless) and when the sun travels highest across the sky casting the shortest shadows at noon. And it’s the time of the longest twilights and the shortest nights. The starry skies are not fully dark until 11 p.m., and they start to lighten again by 3 a.m. It’s also when the full moon travels the lowest across the sky and is visible for just nine hours. Watch for the Strawberry Moon on June 5 as it rises in the southeast around 8:45 p.m. and sets in the southwest the following morning around 6 a.m. Because the moonlight has to travel through so much more of our atmosphere, it will have a warmer honey color compared with the brilliant white moonlight that we saw in winter. 

So head to your favorite ridgetop this month, stand still and be awed by the slow sunsets and golden moonlight of the solstice as we humans have been doing for thousands of generations.

John Heasley is an astronomy educator and stargazer who enjoys connecting people with the cosmos. He volunteers with NASA/JPL as a Solar System Ambassador and with the IAU as a Dark Skies Ambassador. For more information about stargazing in southwestern Wisconsin, like Driftless Stargazing LLC on Facebook and find out whenever there’s something awesome happening in the skies above.

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