Tonight, we will truly have a rare event in the sky, something that we haven’t had for at least 100 years and something we won’t have again for least another 100 years.
We have three for the price of one tonight; a harvest moon, a super moon and total lunar eclipse. Do whatever you can to see this, even if you have to drive a little bit to where the skies are clear. It’s that rare of an event.
Harvest moons themselves are not rare. They occur every year. Astronomically it’s the monthly full moon closest to the date of autumnal equinox, which was Wednesday. Because of where the full moon is among the background stars this time of year, it rises only about 20 minutes later each night. Normally it rises about 30 to 60 minutes later from night to night. We don’t have an outright extension of daylight this week, but the full moonlight keeps the total darkness away for a while, at least in the countryside away from light pollution-plagued areas.
Super moons also are not rare. We also have them every year and last year we had one at harvest moon time. Because of the oblong shape of the moon’s orbit around the Earth, every month it achieves its maximum distance to the Earth apogee, at a little over 250,000 miles, and the closest distance, called perigee, is a little over 225,000 miles. The perigee full moon is actually next month, but it’s close to being one tonight.
There’s no doubt the full moon is bigger in a sky during a super moon but it’s only about 7 percent larger than the average full moon and about 14 percent brighter. I really doubt anyone including myself can really tell the difference in size between an average full moon and a super moon. The power of suggestion can be very powerful.
On the main menu tonight, though, is the total lunar eclipse. It’s the fourth one we’ve had within two years and the last one we’ll see around here until 2019. It’ll be a prime-time event. The eclipse starts at 6:07 p.m. when the full moon starts to slip into the Earth’s ruddy shadow. The moon will be totally eclipsed from 7:11 p.m. until 8:23 p.m.
You don’t need any special equipment to see the lunar eclipse. They’re perfectly safe to stare at for as long as you want with your naked eyes.
Lunar eclipses are wonderful events to witness and this one offers you a unique way to start your day. A lunar eclipse is also a lot more frequent than a solar eclipse and can be seen anywhere in the world where the full moon is visible during the time of the eclipse.
As you can see in the diagram, lunar eclipses occur when the moon in its monthly orbit around our world passes through the shadow of the Earth in the opposite direction from the Sun. This can only happen during full moons but doesn’t happen every time there’s a full moon because the moon’s orbit around the Earth is inclined by five degrees to the Earth’s orbit around the sun. Most months the full moon misses the 6,000-mile-wide shadow, known as the umbra, but not this coming Tuesday morning.
The moon doesn’t totally black out during lunar eclipses because the umbra shadow is not totally dark. Strained sunlight finds its way to the moon through the shell of atmosphere that covers our Earth. Most of the blue and yellow components of the sun’s light is scattered by Earth’s atmosphere leaving only a reddish glow sent in the direction of the moon. This same effect causes orange reddish sunrise and sunsets and has the same effect on moonrises and moonsets.
Enjoy the trifecta tonight of the full harvest moon, super moon, and especially the last lunar eclipse until January of 2019.
Mike Lynch is an amateur astronomer and professional broadcast meteorologist.
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