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Comment by doctoboggan | Hacker News Reader

As a big fan of both the Moon and ciechanow.ski this article is right up my alley.

During the 2024 solar eclipse I was explaining to people how an eclipse must occur during a new moon, and this article would have really helped. The discussion also made me realize how little most people spend thinking about the solar system and the relationship between the moon, sun, and earth. These things fascinate me (I think it's just the sheer scale of it all), and I hope to be able to get more people interested as well. The solar eclipse was great for that!

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People are impressed if you can name the current moon phase and tell them what it'll be next. But it only takes a mental model of where the sun, earth, and moon orbits are relative to each other. I also find people are intrigued by the concept of earthshine, and often haven't noticed it until you point it out.

Earthshine is such a cool phenomenon to point out

> People are impressed if you can name the current moon phase and tell them what it'll be next

I'm speechless

And once you internalize this, every image where there are moons pasted into the sky without understanding this will trigger you. It's like bad kerning. Once you see it, you can't unsee it.

For a waxing moon the circular arc is on the right hand side and for a waning moon the circular arc is on the left hand side [Here in the Northern Hemisphere]. It would have been nice if the mnemonics Decreasing & Cresting worked but they don't. I personally use Developing & Collapsing to refer, respectively, to the waxing and waning moon. Has anyone a better couple of words than these?

In French we have "premier quartier" and "dernier quartier" for "first quarter" and "last quarter" respectively. The mnemonics work with lower case letters: p and d.

In English, the "d" for "decreasing" also works in lowercase, I guess that you can use "p" for "progressing".

> solar eclipse I was explaining to people how an eclipse must occur during a new moon

Hey, that's the first the time I realized this.

And a lunar eclipse only during full moon…. These constraints made it easier to predict eclipses in the past.

Similarly - as full moon must be opposite to the sun, full moon moonrise happens around sunset and moonset happens around sunrise.

Also full moon rises the highest in winter, contrary to the sun - when it’s at it’s lowest[1].

Funny things happen at the poles where sun is above/below horizon for half a year: https://astronomy.stackexchange.com/a/27750

[1] the further from equator you are the more pronounced it is.

The really satisfying thing for me was when I was on a sailing course and was instructed in how the moon causes the tides, and how the phase of the moon corresponds to springs and neaps.

Thinking about how the Moon, a body over 380,000 kilometers away, can perfectly block the Sun (something 400 times larger than itself) because of their relative distances is just mind-blowing for me

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