How many southern constellations can you see in the northern hemisphere?

This question is actually quite difficult to answer ... mainly because the concept is too complicated. First of all, in theory, you can see the starry sky all day in a year on the equator. Then it is no problem to look at the starry sky on the mountain a little north of the equator. There is a calculation formula: at the sea level with latitude a, you can see stars with declination less than 90-A in the other hemisphere. With this formula and some data, you can work out where you can see which stars. But it's still more troublesome to see which constellations. Because the constellation is an area. If you ask a stargazer in Beijing, can you see Scorpio in Beijing? Most people will answer that you can see it. But in fact, you can't see all the bright stars in Scorpio in Beijing. Some small southern constellations can theoretically rise above the horizon, but few stargazers will pay attention to this constellation due to low-altitude occlusion, air pollution and other factors. So the definition of which constellations can be seen is still very vague. Just checked, the latitude of Hainan Island is about north latitude 18, and the declination of Southern Cross is 60, which is just within the visual range. I think there is a misunderstanding: the Southern Cross is in the southern celestial pole. The position of the Southern Cross is actually similar to that of the Big Dipper. It is a constellation representing the south/north celestial pole, but it still has a certain angle with the south/north celestial pole. Therefore, seeing the Southern Cross does not mean that you can see all the constellations in the southern sky.

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