Pull an ‘all-nighter’ with the Harvest Moon
Sadly, we say goodbye to Butler summer this Tuesday evening with the autumnal equinox at 7:04 p.m. Both the northern and southern hemispheres of the Earth receive equal amounts of the sun’s light. Contrary to what you may have learned in grade school, we don’t have equal hours of daytime and nighttime on equinox day. Daytime hours are still winning out! Around here on autumnal equinox day, the days are still more than 10 minutes longer than nights. Night hours won’t beat out day hours until Saturday, Sept. 26. This is all due to the phenomenon of astronomical refraction that bends the sun’s rays so much at the horizon that it appears that the sun is still a little bit above the horizon when it’s actually below it. We cheat nighttime at both ends of the day!
Speaking of next Saturday, no matter how much daylight we get as the week continues, we’ll be lit up big time at night later this week. That’s because we have a full moon officially on Saturday, but it’ll be full for all practical purposes Thursday and Friday night as well. Since the full moon this week is so close to the date of the equinox, it’s considered the annual full harvest moon.
The harvest moon got its name because it lights up the night sky right around harvest time. Now any full moon will rise around sunset and set around sunrise, but astronomically, what makes the harvest moon so special is that it rises only about 20 minutes later each night instead of the usual 45 to 50 minutes later, so there isn’t as much of a gap between the time the sun goes down and the moon rises. The details of why this happens are complicated and, to be honest, somewhat boring. Let’s just say it’s a case of unique celestial mechanics at work where the ecliptic, which is the plane of Earth’s orbit around the sun, is at a very close angle to the horizon in the evening, and leave it at that.
Before headlights were an option on Allis-Chalmers tractors, farmers could use the harvest moon's pale light to extend their time in the field. It wasn’t easy, though. Eagle eyes, strong coffee and determination were also needed for nocturnal farming in the dimmer moonlight. You could easily miss spots. Even now with headlights on tractors the full harvest moon is still a friend to the farmer.
What I’d like to do now is follow the harvest moon across the sky from the eastern to western horizon through the course of the night and point out some of the other highlights in the night sky, although admittedly the fainter celestial treasures will be “moon washed” and tough to see.
When that full harvest moon is on the rise in the evening twilight, it’s a sight to behold. That huge orange orb rising can be breathtaking. No words can adequately describe it. Like any full moon on the rise, it sports an orange hue of varying degrees, depending on the clarity of Earth’s atmosphere. That’s because the moon’s light has to plow through more of Earth’s atmosphere when it’s close to the horizon, and that scatters away all but orange and red components of the moon’s light. When the moon gets higher its light doesn’t have to fight its way through as much atmosphere and it turns white. The moon also seems a lot larger when it’s rising or setting. Believe it or not, that’s just an optical illusion. The same thing happens with the sun and even constellations when they’re close to the horizon.
While you’re getting moonstruck watching the moon rising in the east, look off a little to the lower left and you’ll see Saturn just barely above the eastern horizon on the rise. Through even a small telescope, you should be able to make out the ring system of Saturn, although the ring system and even some of its many moons.
If you’re under the magical moonlight in the midnight hour, the moon will be beaming in the southern sky. With the naked eye you can easily see the dark areas called maria. They are the volcanic plains of the moon. It’s the darker maria you’re looking at when you see “the man on moon.” You might see the poodle on the right side of the moon’s face. That’s my favorite! The white areas are the highlands and mountains. Craters completely litter the lunar surface, and around some of the bigger ones you can see the radial patterns of rays. If you check out our lunar neighbor with a telescope, you might want to slip on sunglasses. It’s so bright you could earn yourself a big time headache and maybe even go a little loony. You can purchase filters that you can insert into your eyepieces to cut down the glare.
While you are enjoying the midnight moon, look in the low eastern sky for a cute little cluster of stars. That’s the Pleiades, otherwise known as the “Seven Little Sisters.” Astronomically it’s a cluster of young stars a little over 400 light years away, all born together about 100 million years ago. By the way, just one light year is almost 6 trillion miles! It’s not a weekend trip to the Pleiades.
If you’re pulling an all-nighter, or if you’re a super early riser before the sun, you’ll see the Harvest Moon heading toward the western horizon and starting to turn orange again. Meanwhile, the eastern half of the sky will be lit up like a Christmas tree with so many bright stars and constellations. I call that part of the sky “Orion and his Gang.” The marquee constellation is Orion the Hunter with three bright stars in a row that make up his belt. Orion’s gang makes up the bulk of the wonderful winter constellations that we’ll see in the evening sky in January and February, but if you’re an early riser this time of year, you get a sneak preview. Among the winter constellations this year, two planets are “renting” space. Mars is easily visible in the constellation with its distinct orange-red hue and Jupiter isn’t far away, a little lower in the eastern sky. A stargazing app like Sky Guide can help you pinpoint the planets, although Jupiter is super easy to locate since it’s the brightest starlight object in the pre-twilight eastern sky.
Enjoy dancing in the full moonlight this week, even if it costs you some sleep. Catch up on that next weekend!
Mike Lynch is an amateur astronomer and professional broadcast meteorologist for WCCO Radio in Minneapolis/St. Paul. He is also the author of “Stars: a Month by Month Tour of the Constellations,” published by Adventure Publications and available at bookstores and at adventurepublications.net. Contact him at mikewlynch@comcast.net.
