Another Supermoon, Already?!

Full Moon at Orange Beach_453745
Full Moon Over Mobile

The full moon of December 3, 2017 is a supermoon. You’re probably saying, “didn’t we just have one last year?” Yes, we did, and we’ve been having them since you walked the Earth, and actually since the beginning of time! What’s different now is social media puts the word “supermoon” in front of you.

“Super” in front of a word might make you think it will be extraordinary or gigantic. “Super” in front of “moon” just means the largest, and that’s largest often by only a small amount. Based on the moon’s orbit around Earth, which is not a perfect circle, sometimes the moon is closer. When it is closest that’s called perigee. When the moon is farthest away and that’s known as apogee. The difference between the two of these is about 14%, for something that is nearly a quarter million miles away.

Here are nine things you need to know about this supermoon.

  1. The full moon of December 3, 2017 will look full on both Saturday night and Sunday night, because it is actually full on Sunday mid-morning, after the sun comes up.
  2. The supermoon (perigee moon) is about 7% larger than average, or about 14% larger than the apogee moon which is sometimes called micromoon. Because it is larger, it will be a little brighter too.
  3. In Mobile, the moon rises at 4:26pm on Saturday, and sets at 6:18am on Sunday. It is full at 9:47am Sunday. It then rises at 5:19pm on Sunday. Sunset on these days is at 4:51pm. Sunrise on Sunday is at 6:34am
  4. All full moons result in higher tides than average, especially when Earth is closest to the sun in our annual orbit. The highest tides of the year are often called king tides.
  5. When the moon rises and sets, it is often tinted red or orange or yellow, for the same reason that the sun takes on those tints when it is low in the sky. Thicker atmosphere filters out the other colors.
  6. When the moon and sun rise, they always appear slightly flattened (oblate) due to the light passing through a thicker atmosphere, closer to the ground, than higher up toward the stratosphere.
  7. When the moon and sun are low on the horizon, perspective makes it seem that they are so much larger than when they are high in the sky. They are not bigger. Prove this to yourself by taking a photo of the moon in both positions (without zooming in) and then comparing photos. You can also compare the moon to the size of your pinky when you stretch your arm out and you’ll see it’s the same size in both positions.
  8. There is no 100% accepted definition of a supermoon. That’s why some years you may hear of more than one.
  9. All great pictures you see of full moons are taken with telephoto lenses on professional cameras, on tripods. That’s why they seem so large and perfect!

Alan Sealls


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