Why Neil deGrasse Tyson is Wrong about the Supermoon

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I don’t know much about astronomy, but I am a scientist and I know this. One key scientific concept that is rarely grasped by non scientists but at the same time drives much of science itself is variation.

Indeed, the understanding that variation is key is one of the characteristics that separates the ancients, who may have engaged in what looks like science but rarely advanced true understanding, and the moderns (to oversimplify greatly, ironically).

The moon and other celestial bodies always do the same thing, never change in their course or appearance, and once one has finished cataloguing them, there is nothing else to see.

Or is there? Isn’t there in fact change all the time? Isn’t change itself the essence of the universe? Is it not true that a star is a dynamic thing that has a birth, stages of life, a death, and from its remnants come other things? Isn’t this how astronomers like Neil DeGrasse Tyson are able to utter such brilliances as “I am made of star dust”??? Don’t planets form, collide with things or things with them, cool, change dramatically across the surface, even break lose form their orbits now and then?

It turns out that the Moon varies over time in its physical relationship to the Earth, because orbits are not perfectly simple geometric shapes. It turns out that this variation in orbital geometry, of the moon in relation to the earth, and the earth in relation to the sun, is incredibly important. You know tides are important. Regular readers of this blog also know that variations in tides from day to day, caused by this orbital variation, also matter. You know that the sun provides energy to warm the surface of the Earth (the atmosphere, the ground itself, the seas and lakes, etc.). Readers of this blog also know that variation in orbital geometry is one of the factors that cause immensely important variation in that process. Day vs. night is a big deal, seasons are a big deal, and the changes in the nature of day and night and seasons over time scales of tens of thousands of years are among the key determinants in whether or not we have ice ages. That sort of thing.

The so-called “supermoon” is a phenomenon whereby the moon is sometimes closer to the Earth than at other times, and thus looks bigger and is brighter to our eye. The difference between the smallest looking moon and the biggest looking moon is about 14% in apparent area and 30% in apparent brightness. That brightness difference is comparable to differences between different size light bulbs one might choose, or maximum and minimum difference in screen brightness one might set for a smartphone or laptop screen. Most people would, and do, spend considerable effort and energy appearing to be 14% different in size (one way or anther). That is not a small amount.

So, with the supermoon, two things can happen. One, regular people who are not scientists can get a taste of variation, to understand that the fixed objects of our solar system arent’ so darned fixed, and in fact vary impactfully in the way they relate to each other. That can lead to interesting discussion if one lets it. Two, the supermoon phenomenon, an astronomical phenomenon that is real, can lead more people to get outside and look up into the sky at stuff.

But Neil deGrasse Tyson, enigmatically, will have none of it. He says stay inside, don’t look up, don’t engage with the cosmos. The supermoon is nothing. NdGT tweeting:

Note: that is an anti-science technique known as cherry-picking. One does not measure the magnitude of variation by comparing two adjoining points along a series showing change. One looks at the maxima and minima. Sorry, Neil, this is what climate science deniers and the like do. 🙁

Note: That is true of the moon at all times. Photographing the moon impressively is hard, as is the case with all nighttime photography, and all astrophotography. But, if one in ten thousand people who take a picture of the moon with their smart phone and find disappointment are inspired to strive for more, and become amateur astrophotographers, the supermoon is a win.

Neil, you need to take a breath, remember your roots (you were the always the guy on TV telling everyone to get outside and look up!), and rethink this. Put the supermoon in proper context and help people understand it, and encourage learning. Don’t cherrypick and belittle a phenomenon, tell people that actual variation in a natural system isn’t really there, and discourage engagement with the natural world.

Just as disappointing (and yes, this is a post about me being disappointed that someone is wrong on the Internet.) as Dr. Tyson’s tweetish mooning of the supermoon is the slobbering fanboy/girlism whereby so many fall into this trap (I won’t repeat the tweets, but you can go and look.) I applaud and thank the others, some astronomers or other scientists, who have pushed back on Twitter.

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21 thoughts on “Why Neil deGrasse Tyson is Wrong about the Supermoon

  1. Sorry Greg, but Neil is totally correct.

    Tape a quarter to a wall. Now take a pencil, hold it at arm’s length, and back up until the width of the pencil just covers that quarter (helpful hint – the pencil and the moon are both about 0.5 degrees). Now look really carefully at that quarter, and how big it looks.

    Now a month later, repeat with a nickle, and compare to your memory of last month’s quarter.

    Can you tell the difference?

  2. Valdis, that is simply not the point, of a pencil or anything else.

    And actually, yes, I’m pretty sure I can tell 30% difference in brightness of an object. Most people can.

    If you pay attention to the moon enough you’ll notice all sorts of interesting variation. For example, how long it takes to set in the temperate winter sky vs. on the equator, or its apparent brightness or color depending on sky conditions, etc.

    NdGT and you are agreeing that there is no meaningful variation in the moon. I’m saying that variation is key in science, and that we can use the moon as an example of that.

    (Not quite sure why I’m repeating the contents of my post, it is pretty clear in the original!)

    1. _NdGT and you are agreeing that there is no meaningful variation in the moon._

      There’s no meaningful variation easily visible to the naked eye. And you’d be surprised at your inability to detect a 30% difference across a month unless you had a lot of experience in keeping track of such things. Remember, this isn’t a real-time A/B comparison. If you visited a friend’s house, and they had a 100 watt bulb in a fixture, and then you visited a month later, and they had a 60 watt bulb there, would you be able to detect it?

      Bonus points for factoring the fact that most people now live in highly light-polluted places, so the 30% change in the moon’s brightness isn’t even a 30% change in total illumination.

    2. Actually, most people can’t, the difference between the apogee Moon and the Perigee Moon, roughly 6 months apart, is the width of three human hairs, some dedicated amateur astronomers with good visual acuity can, but I am also a dedicated amateur astronomer with ordinary visual acuity and I can’t (I have photographed them though). Ordinary people without visual referents have no hope.


  3. Yeah, shooting the moon with just a 70-300 + a 1.5 telezoom add-on is hard. So why discourage the supermoon phenomenon which is when the conditions can be at their optimal for anybody in the cities and suburbs (not like we can all step out into the middle of Yellowstone or Monument Valley for a sky with no light noise).

    Each time I go out, with the lessons learned from the last time, to make another attempt, to find the optimal conditions in the sky and the optimal conditions in my camera. It is the scientific method in action: studying past shoots and data, makie a prediction of the settings you want, shooting with them and also with the settings you used last time as your ‘control’ (you should have more or less reproduced your conditions last time, testing your own discipline), and examine the results…then post your best shot for feedback and advice from those who have been doing this longer than you.

    It isn’t ‘science’, no, but it is an example of how the discipline of the scientific method can be applied in every day or artistic life. The lessons, the discipline, of scientific thinking can be applied in other aspects of human activity, and in doing so you then can appreciate the work that science does even more.


    1. Joseph: Thank you for pointing out that even you, with a camera, and *looking* for changes, have to go through an iterative process.

      Also, note that these days not a lot of people use a camera with a 70-300 lens…

  4. The guy’s been teaching astronomy since he’s 15, and you’re calling him wrong. Not even wrong, but misleading while completely correct.
    Before that you praised Bill Nye for a video where he tested football pressure by hand and said it feels the same.

    1. The issue is that NdGT has two roles that he is known for, and in this one case they seem to contradict.

      On the one hand, he generally exemplifies the love of science and tries to spread that love to those who would not otherwise feel it.

      On the other, he generally exemplifies the skepticism of science and tries to spread that skepticism to those that would otherwise embrace foolishness.

      But unlike his mentor Sagan, he lets his skepticism overrule his other role. Sagan never did that. He found ways to encourage skepticism WITHOUT discouraging curiosity. It was, as we’ve since realized, a very special gift.

      Tyson hasn’t quite mastered that, and lets his push for realism and skepticism discourage curiosity, and THAT is what Greg I believe is writing about here.

  5. I wonder if anyone ever considered the refraction index of the atmosphere and that seeing the moon at a lower angle in the sky is through a larger volume of the atmosphere than seeing the moon higher. Does this have any significant magnification or distortion quality?

    1. Fred, that is part of a lively discussion related as well to the claimed phenomenon that when the moon nears the horizon when viewed at the equator, it seems to speed up and set really fast. Subjectively, I sort of feel like I’ve seen this but I can’ t rule out that I was just distracted and it went and set while I wasn’t paying attention for a moment.

  6. Lunar Perigee is 362600 km while apogess is 405400. Which gives a variation in apparent diameter of about 12%.

    Variation in apparent area of the moon is about 1.12^2 which is about 1.25. So an apparent change in brightness of the moon of about 25%. This isn’t trivial.

    It’s true the full moon prior to the super moon is only a little different than a full moon. But this is like saying the tide twenty minutes before high tide is only a little lower than high tide. Tyson’s only looking at a small part of the range of variation.

    While Tyson’s comment is kind silly and pedantic, it doesn’t really qualify as an error in my book. For flat out errors see the webpage Fact checking Neil deGrasse Tyson. I believe you can click on my avatar to get to it. Or Googling “Fact checking Neil deGrasse Tyson” works

  7. Hop: Unless you live in the Bay of Fundy, 20 minutes before high tide *is* only a few inches at most lower than high tide. At most locations, the tide level is fairly well approximated by a sine wave, so at the max and min points the values for a fairly wide window either side are still pretty close. Visit a beach – the high point of waves moves up and down the beach the fastest about 6 hours away from high/low tide. That half hour either side, those waves are breaking right about the same place….

    1. What you, Hop, and Greg are saying is something that makes it more difficult for casual observers to notice variations in many things. At a casual glance it is difficult to tell a full moon from the gibbous moon phases seen for a couple of days before and after.

      When I was teaching, I was often surprised at the things that people hadn’t noticed about the natural world.

    2. Valdis Kletnieks writes “Unless you live in the Bay of Fundy, 20 minutes before high tide *is* only a few inches at most lower than high tide.”

      Correct. That is my point — which you apparently missed.

      The size of the full moon prior and subsequent to a super moon are nearly the same as the super moon. But that’s not the full range.

      You wait six or seven full moons and you’ll have a full moon 89% the diameter and about 20% dimmer.

      “At most locations, the tide level is fairly well approximated by a sine wave,”

      If you want to look at the full range of a sine wave you need to go at least 180º. Sin 90º = 1. Sin 270º = -1. What Tyson’s doing is like comparing sin 70º and sin 110º to sine 90º and saying there’s only a variation of .06.

  8. Tyvor: It’s amazing how many people were in the 70-90% totality zone of the recent eclipse and didn’t notice a thing, because human vision is highly adaptable to variance in illumination.

    Yes, if you have actual photography gear up to the task, or have Tycho Brahe’s naked-eye observation skills, or have plenty of time to look at the moon every night (and day during most the month when it’s easily visible in daytime at one time or another – another thing a lot of people don’t realize), you can notice things like where it rises and sets at different times of year, etc. Hell, Stonehenge got built based on that sort of observation.

    But if you live anyplace light-polluted, and you’re going outside just because you saw a Facebook post bragging a Super Moon tonight, you’re in for disappointment.

  9. Thank you, I completely agree. I am not a scientist, I am an artist and writer. I am outside in the garden at night a lot. I have had the experience of noticing when a full moon is brighter than normal, only to go back in, look online and find that there is a so-called super moon happening. Maybe Neil wouldn’t notice the difference in a 30% brighter moon, but lots of people do, especially people who are paying attention to the world around them. And I too think he should be encouraging people to notice changes in nature, even small ones. There is value in learning to appreciate the small things.

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