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Starwatch: Pull an ‘all-nighter’ with the harvest moon

September 22, 2018

Sadly, we say goodbye to summer this weekend with the Autumnal Equinox at 8:54 on Saturday night.

Even though both the northern and southern hemispheres of the Earth receive equal amounts of the sun’s light, you don’t have a better chance of balancing an egg on its end today than you do any other day of the year. Another myth about the Autumnal Equinox is that the hours of day and night become equal. Daytime hours are still winning out! Here in Rochester on Autumnal Equinox day, the days are still more than 10 minutes longer than nights.

Night hours won’t beat out day hours until next Wednesday, Sept. 26. This is all due to the phenomena of astronomical refraction that bends the sun’s rays so much at the horizon 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!

No matter how much or little daytime we get this week, we’ll be lit up nearly all 24 hours with sunlight by day and moonlight by night. That’s because we have more or less a full moon all this week. The exact night of the full moon this coming week is Tuesday night, and since the full moon this week is so close to the date of the Autumnal Equinox, it’s the annual full Harvest Moon.

Full moon rising

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 with you 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 take advantage of the Harvest Moon with its pale light to extend their time in the field. It’s not 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. That inconsiderate neighbor of yours can mow his lawn by the light of the silvery Harvest Moon and drive you up the wall!

March across the sky

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 upper right and you’ll see at least two bright planets low in the sky on either side of the southern horizon. They are Mars, hanging closest to the moon, and Saturn, found a little farther away in the low southwest sky. Mars has definitely dimmed in brightness from last month when it was at its closest point to the Earth in 15 years. Through even a small telescope you should be able to make out the ring system of Saturn, and some dark blotches on Mars, which are part of its extensive valleys. Both planets might be a little fuzzy because they’re so close to the horizon, especially Saturn.

Ave Maria

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, I would highly advise looking though sunglasses. It’s so bright you could earn yourself a big time headache and maybe even go a little looney!

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.

Comes the dawn

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! As a bonus, the brightest star you can see in the east is actually Jupiter making a visit this year to Orion and his gang.

Enjoy dancing in the full moonlight this week, even if it costs you some sleep. Catch up on that next weekend!

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