The harvest moon has good company
Sadly, summer officially came to an end this weekend. Saturday at 1:50 a.m. was the moment of the autumnal equinox. That’s when the sun slips below the celestial equator, a projection in the sky of the Earth’s terrestrial equator.
From day to day and week to week until Dec. 21, the sun’s arc across the sky will get lower, and the days will become shorter as we dive toward winter.
In the meantime, we still have plenty of daylight, and our nighttime hours are bright with moonlight over Butler. That’s because we start this week with a football-shaped waxing gibbous moon. We’ll have a full harvest moon on Friday since it’s close to this year’s autumnal equinox.
The harvest moon was named because it lights up the night sky around harvest time. Like any full moon, it rises at sunset and sets around sunrise. What makes the harvest moon so unique is that it rises only about 20 minutes later each night instead of the usual 45 to 50 minutes, so there isn’t as much of a gap between the time the sun goes down and the moon rises.
Why this happens is a complicated story, as it comes down to unique celestial mechanics at work. This week, the ecliptic, the plane of Earth’s orbit around the sun, is at a very close angle to the horizon in the evening.
Before headlights were an option on John Deere tractors, farmers could take extra advantage of the harvest moon with its pale light to extend their time in the field. They still needed eagle eyes, strong coffee, and sheer determination for nocturnal farming in the dimmer moonlight, and you could easily miss spots. Even with headlights on tractors, the full harvest moon is still a friend to the farmer.
When that full harvest moon is on the rise in the evening twilight, it’s a sight to behold. It’s 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 must plow through more of Earth’s atmosphere when it’s close to the horizon. All but the orange and red components of the moon’s light are scattered away.
When the moon gets higher, its light doesn’t have to fight through as much atmosphere and 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 happens with the sun and even constellations when they’re close to the horizon.
To the far upper right of the harvest moon, you’ll see a moderately bright “star” shining in the low southeastern sky. That’s Saturn, an absolute joy to view through even a small telescope. You can easily see its ring system made of ice and at least some of its moons, especially its largest moon, Titan, which is larger than the planet Mercury. Saturn is just over 830 million miles away tonight, so far away that its light takes over an hour to reach the Earth!
To the lower left of the harvest moon, you’ll see a super bright “star” rising above the eastern horizon. That’s Jupiter, nearing its closest approach to Earth this year. Jupiter is about 385 million miles away this week, but in early November, it will only be 370 million miles away if you’re making travel plans!
As the largest planet in our solar system climbs above the horizon, remember it’s so large that over a thousand Earths would fit inside it! Jupiter is also an excellent telescope target. You can easily see up to four of its brightest moons as they orbit the big guy in periods of two to seventeen days. You can also detect some of its more brilliant cloud bands. It’s best to wait until after 10:30 to view Jupiter with your telescope so it can rise above the blurring effects of our atmosphere close to the horizon.
In three weeks, there won’t be another full moon but rather a blocking moon. On Saturday, Oct. 14, in Butler, we’re going to have a partial solar eclipse as the new moon will partially pass in front of the sun.
A little after 1 p.m. during the eclipse peak, just over 40% of the sun’s disk will be covered by the moon. On April 8 next year, there’ll be a nearly total eclipse and in extreme northwestern Pennsylvania it will be a total eclipse that’ll be spectacular and worth traveling to see! I’ll have more on all this next week in Starwatch
Mike Lynch is an amateur astronomer and retired broadcast meteorologist for WCCO Radio in Minneapolis/St. Paul. He is the author of "Stars: a Month by Month Tour of the Constellations," published by Adventure Publications and available at bookstores and adventurepublications.net. Contact him at firstname.lastname@example.org.