Minute Physics has a new series called Physics explained in 9.9999s and these short videos can explain a lot in only a few seconds. Kudos to Minute Physics for this hard work. In the video from above we undertsand that the tides are created by Moon’s gravitational pull.
In the video from below we learn that Celsius and Kelvin temperature degrees are counted differently and 0 Kelvin is the lowest it can get:
Time dilation occurs due to the fact that time flows differently (slower) if you move at a speed of 0.87c or if you are closer to a center of gravity:
Negative Celsius temperatures are possible, but negative Kelvin temperature or absolute negative temperatures are possible? Yes, and this is due to the fact that we define temperature as the speed at which molecules wobble when they receive energy (or how disorderly the molecules get). If all the molecules stop from wobbling, then that is 0 K.
If you get a quantum system in which you can insert more energy, but the molecules get more orderly and stay in the same place, then you get negative absolute temperatures, but still positive energy.
There are about 5116 stars that we can see with the naked eye, many billions in the observable Universe and maybe an infinite in the whole Universe: