Monday's wallpaper!

[skybreak]

http://www.girlgeniusonline.com/comic.php?date=20180212

The Castle and The Train remind me of my cats. They'd both sometimes sit/play on me in the middle of the night.

Comments

[madfilkentist]

You've got me trying to work this out, though orbital mechanics is far from my strong point.

Some scattered thoughts: It's opposition to the Sun, not the time of sunrise, which makes the Moon full. According to Wikipedia, in sufficiently northerly latitudes the Moon can be above the horizon all night or be above the horizon for just a short time or not rise at all for a day. This depends on the Moon's current latitude in its orbit, not on the solar season.

The full moon has to be roughly opposite to the sun with respect to the Earth. That says you can't have a full moon when the Sun is much above the horizon. But given the Earth's axial tilt and the Moon's orbital inclination, it isn't obviously impossible (to me) that the full moon could be close to the horizon at 3 AM in England.

If someone who isn't just guessing could give a better explanation, I'd be grateful.

[murgatroyd666]

tl;dr: Yup, my explanation wasn't clear, and it's a complicated situation. Without looking up some key numbers or doing the math, my guess is that it is possible.

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Your explanation is more lucid than mine, but I was aware of what you're saying here ...

It's opposition to the Sun, not the time of sunrise, which makes the Moon full.

The moon is full when it's opposite the sun. Sunrise is when the sun is at the horizon, so that's when you can guarantee that the full moon is near the horizon too (but 180° away from the sun along the circle of the horizon).

According to Wikipedia, in sufficiently northerly latitudes the Moon can be above the horizon all night or be above the horizon for just a short time or not rise at all for a day. This depends on the Moon's current latitude in its orbit, not on the solar season.

Right about the latitude ... but the plausibility depends on the season, too. Nights are shorter in the summer (i.e., sunrise is earlier), so it's easier to compose this scene if the wallpaper image depicts a summer night. Also, Agatha doesn't look cold!

Yes, the closer the observer is to the north or south pole, the nearer the full moon can be to the horizon at other times during the night (and during the day as well). That's why I mentioned high latitudes. Inside the Arctic Circle all bets are off, and due to the inclination of the moon's orbit to the plane of the earth's equator, you can have the full moon on the horizon at 3:00 a.m. at even lower latitudes. But how low?

My question was whether the latitude of England was too low for things to work out. And I asked because I was too lazy to look up the inclination of the moon's orbit and the latitude of London and then do the spherical trig! The more I think about it, the more plausible it seems to me ... but as I said, I haven't done the math.

Could it be that Agatha is enjoying a warm summer night in Tromsø?

Complicating things further, the moon doesn't have to be exactly opposite the sun to look "full" ... in fact, if it were exactly opposite the sun, the moon would be in eclipse! But it looks very full in the Professors' depiction -- say, within five degrees of being counter-solar, or ten moon-diameters away from the counter-solar point.

Interesting fact: The path of the moon through the sky is close to the ecliptic -- the path of the sun and the planets in the sky. Unlike almost all other satellites in the solar system, the plane of the moon's orbit isn't aligned with the equator of the planet that it orbits; it is much better aligned with the general plane of the orbits of the planets around the sun.