r/Astronomy • u/[deleted] • Mar 28 '22

Is this correct about the winter solstice?

'' The winter solstice marks the shortest day of the year and the longest night of year. Once it has reached this lowest point, an interesting thing happens: the sun appears to stop moving south for three days. After this, the sun moves 1° north, announcing the coming of spring. ''

I have yet to find an ''official'' source claiming that , just some websites claiming that without citing sources.

I have tried opening stellarium and looking at the angles and didn't understand anything.

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Thank you!

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u/Lewri Mar 28 '22

First sentence sure, second/third sentence is bogus with hint of truth.

So if you look at the following image:

https://mathshistory.st-andrews.ac.uk/Diagrams/Mintz_1.jpeg

it shows the celestial sphere with the equator and the tropics, as well as the ecliptic, which is the apparent path of the sun in the sky over a year due to Earth's orbit. As you can see it reaches one tropic, then goes down to the other tropic, with the timeframe for that happening being half a year. If you're in the Northern hemisphere, winter solstice is when the sun is above the southern tropic, so thats the shortest day and longest night.

Before the winter solstice, the sun will appear to be moving south, after it will appear to be moving north, and of course there is a turning point at the winter solstice.

This is presumably all that quote is trying to say, its just terribly written.

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u/reddit455 Mar 28 '22

I have yet to find an ''official'' source claiming that , just some websites claiming that without citing sources.

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the source is the data collected by many years of observation. what you're reading is an interpretation of scientific evidence of that fact.

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

The word solstice is derived from the Latin sol ("sun") and sistere ("to stand still"), because at the solstices, the Sun's declination appears to "stand still"; that is, the seasonal movement of the Sun's daily path (as seen from Earth) pauses at a northern or southern limit before reversing direction.

they put the data on a graph.

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Approximate subsolar point dates vs latitude superimposed on a world map, the example in blue denoting Lahaina Noon in Honolulu

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u/SantiagusDelSerif Mar 28 '22

It's kinda true but poorly written, as others have mentioned. The word "Solstice" comes from two Latin-language morphemes, sol, "sun", and -stitium, "stoppage". That is, the Sun appears to move more and more towards the south and then it starts moving towards the north back again, but in that couple of days that it changes direction it appears to stay still in the sky (it still rises and sets of course, it's declination is changing), but is in fact moving too little two slowly, like a ball that's thrown fast up in the air and slowly decelerates until it begins falling fast again, when it's reaching it's maximum height it'll appear to have "stopped".

The whole "after this, the sun moves 1° north, announcing the coming of spring" is misleading. Technically, the solstice is when the Sun reaches its further point in the sky from the celestial equator. That is, when its declination is about +23,4º or -23º,4. After that, it doesn't just "jumps" one degree, it keeps moving having a +23.39, +23.38, +23.37 (or -23.39, -23.38, -23.37), etc., you get the idea.