Driftless Dark Skies: Autumnal Dawn

September 8th, 2017 by John Heasley

We think of evening as the ideal time for stargazing. The sun sets, the sky darkens, and one by one the stars and planets emerge. If you look to the east just after sunset, you can see Earth’s shadow just above the horizon. Darkness does not fall—it rises! We spend the night in the shadow of the Earth. You can watch the Crescent Moon as it waxes and passes near Jupiter low in the west on September 21 and 22 and just above Saturn in the southwest on September 26. 

Evening is only part of the show. The days around the autumnal equinox on September 22 are perfect for stargazing at dawn. The sky begins to brighten around 5:15, and the Sun rises around 6:45. Those 90 minutes are the best time. One by one, the stars and planets begin to fade and disappear, just as one by one the birds begin their songs. Morning planets often appear highest above the eastern horizon around the equinox, and you can watch three of them dance as they approach and pass one another. 

Mercury is often challenging to see. It’s the innermost planet and stays pretty close to the Sun, but you can spot it low in the east near the bright star Regulus on September 9 and 10. Mercury is the brighter of the two. Mars, dimmer and redder, is below and to the left of the pair. Your binoculars will help as you scan the sky right above the horizon. Mercury will be its highest above the horizon on September 12. Watch as Mercury moves closer to Mars until they are almost inseparable on September 16. Arcing above them in a line, you will see bluish Regulus, dazzling Venus, and the waning Crescent Moon. On September 17, the Crescent Moon is slimmer and has moved closer to Venus. By September 18, the Moon has waned even more and shines between Venus and Regulus above it and Mars and Mercury below it.  See if you can spot Earthshine on the dark part of the Moon. That’s sunshine reflected from Earth and brightening the night side of the Moon. 

Autumn also means that the Universe in the Park programs come to a close. We have one more opportunity at Governor Dodge State Park on September 23 and two more at Wildcat Mountain State Park on September 2 and 30. UW grad students give a talk in the Amphitheater and then set up telescopes for guests to have a look. Starsplitters of Wyalusing offer public programs on September 16 and 23. If skies are clear, we should be able to see the moons of Jupiter, the rings of Saturn, and the craters of the Moon. Hope you enjoy the skies at dawn and dusk! 

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. For more information about stargazing in southwest WI, like Driftless Stargazing LLC on Facebook and find out whenever there’s something awesome happening in the skies. Driftless Dark Skies appears monthly in the Voice of the River Valley.