[cgriswald]

To play devil's advocate:

* Supermoon lunar eclipses are uncommon. * The visible difference can be up to ~14%, and its significantly brighter too.

But viewing the moon on the horizon will get you a bigger apparent size difference, no supermoon needed.

[dalke]

I believe the definition of 'supermoon' is 'closer than 90% of the time", so yes, it happens for about 10% of all eclipses.

Let's coin 'superdupermoon' for the 1% case.

And ... so what? As http://science.nasa.gov/science-news/science-at-nasa/2011/16... points out:

> Okay, the Moon is 14% bigger than usual, but can you really tell the difference? It's tricky. There are no rulers floating in the sky to measure lunar diameters. Hanging high overhead with no reference points to provide a sense of scale, one full Moon can seem much like any other.

About once a year Jupiter is in opposition. Should we call that a "super Jupiter"?

[cgriswald]

> I believe the definition of 'supermoon' is 'closer than 90% of the time"

Within 90% of perigee, yes.

> it happens for about 10% of all eclipses.

Hayley's comet is visible for 100% of its orbits. It's passing is still a rare event because it happens typically once in a lifetime. A supermoon lunar eclipse will happen maybe half a dozen times in yours. It's an uncommon event.

> And ... so what?

If you're not interested, you're not interested. I don't like the term supermoon either. But it's interesting to me that the difference is measurable. Photographing the full moon at perigee and apogee and measuring the difference is my kind of fun.

[dalke]

In your position as devil's advocate, how does your parallel to Halley's comment provide any justification to your counter-argument? We don't have a special term for a comet when it's within 10% of perihelion.

Again, remember that you were being a devil's advocate. My "so what?" comment was mean to highlight the weakness of your counter-argument. It's not actually significantly naked-eye brighter but requires instruments to measure. Now you've jumped to something outside of the role that you've assigned yourself, because you switched to talking about 'your kind of fun' and using instruments to help with your fun. That's a very different topic than what you started with.

Saying "X is an uncommon event" does not, on its own, justify or explain anything. There are millions of rare events every day. Should we celebrate when Jupiter is at perihelion? That's only once every 11.86 years. What about when Mars is in aphelion? 67P/Churyumov-Gerasimenko was at perihelion on 13 August 2015 - did you celebrate?

[cgriswald]

> In your position as devil's advocate, how does your parallel to Halley's comment provide any justification to your counter-argument?

I was merely pointing out that NdGT comments, while factual, were not really on point. I could also have said, "So what...?"

My arguments against the term supermoon are: 1. It piques public interest and then fails to deliver. 2. We have proper terms for the events that are occuring and should be using those terms instead.

Certainly these are stronger arguments than "But it doesn't look any bigger!"

But you're trying to place my "devil's advocate" role in the wrong context. Clearly the frequency of lunar eclipses has nothing to do with the term supermoon.

> how does your parallel to Halley's comment provide any justification to your counter-argument?

I think the point was rather clear. You were trying to argue that supermoon eclipses were not uncommon because they occur for, on average, 10% of all eclipses, but that was not the right metric. The occurance of these events over time is the correct metric.

> It's not actually significantly naked-eye brighter but requires instruments to measure.

It is 33% brighter. I would be surprised if that isn't detectable by the human eye. It certainly looks brighter to me tonight.

You don't need serious instrumentation to measure the change in size. Hold a quarter up to it so it just blocks out the moon. Measure the distance between your eye and the quarter. Now do the same when the moon is at apogee.

If you want to get technical, I don't really understand why it matters whether the difference is naked-eye visible or requires instrumentation. The prefix super- doesn't require it.

> Should we celebrate when Jupiter is at perihelion?

Are we celebrating? Certainly we "celebrate" in the form of news articles and increased observation when Jupiter is at perihelion, and, as you note, this event occurs once every ~12 year–more frequently than perihelion-sygyzy of the moon, Earth, and the sun. Although I think if it coincided with an eclipse of Jupiter by the Earth we would probably be too busy panicking to celebrate.

But these comparisons to other astronomical bodies don't hold water. The Moon holds a different place in our collective consciousness than these other astronomical bodies. Ask someone to point out Jupiter and most people won't be able to do so. Ask them to point out the Moon and everyone will be able to do so.

Supermoon, superjupiter, super67P/Churyumov-Gerasimenko are not incorrect. Why does the moon get special treatment? Probably for the same reasons it often does.

[rev_bird]

Clearly that would be a Supiter

[jsprogrammer]

Do objects really get a larger apparent size at the horizon? I guess there might be a small magnification effect from the additional atmosphere and angle?

[aaronbrethorst]

I assume it's the result of our brains being better able to make a size comparison when the moon is at the horizon.

Here's an example I shot two full moons ago: https://www.flickr.com/photos/aaronbrethorst/20189872605/in/...

The moon looks absolutely monstrous here, but, I expect that if I had measured it when it was high up in the sky, the actual apparent size wouldn't have been any different.

[ezequiel-garzon]

Possible explanations have only appeared in recent years. It looks like by trying to make an adjustment your brain gives you a distorted image. Truly amazing.

https://en.wikipedia.org/wiki/Moon_illusion

[jsprogrammer]

Ah, so as I thought. There is no difference in apparent size.

>A simple way of demonstrating that the effect is an illusion is to hold a small object (say, 1/4 inch wide) at arm's length (25 inches) with one eye closed, positioning it next to the seemingly large Moon. When the Moon is higher in the sky, positioning the same object near the Moon reveals that there is no change in size.

[cgriswald]

Yes. Not just the moon, but constellations as well. Maybe other things. There's no consensus on why. Refraction is one idea. Another is its the way our brains process the information from our eyes.

[jsprogrammer]

Brain processing shouldn't affect apparent size. Apparent size can be measured easily. I'd guess the difference in apparent size between something at zenith and on the horizon is less than a percent.

[cgriswald]

Sorry, I meant how it appears to you, not it's apparent size.

[jsprogrammer]

I've been getting the moon in perfect view from my kitchen window for the last several evenings. It gets great framing from the treelines on the local hills and the walls of nearby buildings. I think the framing helps you to focus on the moon (it's relatively bright compared to the rest of the scene) and appreciate the detail (some of which you can actually see with decent human vision). You are also seeing it right next to objects that you have more familiarity with their size, which helps you to appreciate the scale of the object.