u/its_brielove

The seasons are caused by earth's tilt, I know that. What I don't understand is why the hemispheres alternate being closest to the sun.

For example, say the northern hemisphere is in summer and it's pointed to the sun. Why is it pointed away from the sun in winter, instead of always pointing toward the sun? Does that make sense? Like, why doesn't the earth spin that way, too?

Does it have to do with earth's or the sun's gravity? If the northern hemisphere were more dense, then would it always be towards the sun because of the sun's gravity?

I'm an environmental science nerd, not exactly a space nerd-- though I know the two are closely related. Either way, this is confusing. If you understand what I'm trying to say, please help me out 😅

So, I know that we (humans-- no aliens here, totally--) breathe in oxygen (O2) and release carbon dioxide (CO2). But I also know that 78% of the air we breathe is nitrogen compounds, and only 21% is oxygen, with the last 1% being other gases such as CO2 with .04% (source).

As far as I'm aware, humans don't have super high tech air filters in our nostrils, trachea, or bronchi to separate these gases, so... what happens to the air that's not oxygen? Do we breathe that in too?